Physico-chemical modification is understood as a targeted change in surface properties as a result of technological external influence. This refers to a change in the structure of the material in thin surface layers due to physical impact (ion and electron beams, low-temperature and high-temperature plasma, electric discharge, etc.) or chemical impact, leading to the formation of chemical compounds based on the base material on the surface of the layers (chemical , electrochemical and thermal oxidation, phosphating, sulfidation, plasma nitriding, etc.).
It is obvious that there is no clear classification boundary between the processes of physicochemical modification and surface hardening.
Among the many methods of physicochemical modification, the most promising are ion implantation, anodization, in particular pulsed (processing in electrolyte plasma), and laser hardening.
Ion implantation is a relatively new method of physicochemical modification based on the introduction of accelerated ions of alloying elements into the surface layer.
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Rice. 19.12. Diagram of the installation for ion implantation with a linear accelerator (A ) from D-implantaiii (b):
1 - ion source; 2 - ion extraction system; 3 - separator; 4 - focusing magnets; 5 - linear accelerator; 6 - electrostatic deflection system; 7 - ion flow; 8 - hardened parts
The implanted ions have a shallow penetration depth, but their influence extends much further from the surface.
The following features of ion implantation can be distinguished:
The possibility of forming alloys on the surface that cannot be obtained under normal conditions due to limited solubility or diffusion of components. In some cases, the equilibrium solubility limits are exceeded by several orders of magnitude;
Doping is not associated with diffusion processes, with the exception of the modification of ion implantation materials at high current densities, when radiation-stimulated diffusion of components is observed;
The process takes place at low temperatures (less than 150 °C), without changing the mechanical properties of the material. The method allows the processing of heat-sensitive materials;
There is no noticeable change in the size of parts after implantation;
Modified surfaces do not require further finishing;
The process is well controlled and reproducible;
Ecological cleanliness of processes;
Only exposed surfaces directly exposed to ion irradiation are hardened;
Small depth of the modified layer;
Relatively high cost of equipment.
The installation for implantation with an ion beam contains an ion source, an ion “pulling” system 2, an ion separator 3, magnetic focusing lenses 4, a linear accelerator 5, and an electrostatic deflection system b. In practice, continuous and pulsed ion sources of various designs are used, generating ions of gases (from hydrogen to krypton) and metals (with hot and cold cathodes, magnetron, diaplasmtron, etc.). The ions leaving the source are heterogeneous in composition. To separate foreign ions, a magnetic mass separator is used, which deflects ions that have a different mass and charge from the main axis. The “purified” ion beam is focused and accelerated in a linear accelerator. Scanning of the ion beam over the surface of the part being hardened is carried out by a deflection system 6 .
To ensure uniform hardening, the part rotates and rotates relative to the beam.
Ion implantation with plasma ions - sometimes called 3B implantation - is performed in vacuum chambers, where an ionized environment is created by a glow or arc discharge, and a pulsed high voltage is applied to the part, which ensures the acceleration of ions in the direction of the bombarded surfaces. A high-energy ion flow can be formed directly during the combustion of a pulsed self-discharge between a grounded vacuum chamber and the product that is the cathode.
Ions accelerated in the cathode incidence field of small thickness effectively modify the surface of the product, which can have a complex volumetric shape. Incident ions generate an electron beam from the surface of the product, which, interacting with the plasma, ensures self-sustaining discharge. This method has certain advantages over radiation methods due to the simplicity and relatively low cost of implementing technological processes. It can be combined with other ion-plasma processing methods, such as magnetron, vacuum-arc and plasma-thermal sputtering, ion nitriding, etc.
High-energy ion implantation uses gas ions with energies up to 100 keV to strengthen metals and alloys, ceramics, and polymers.
Treatment with high-energy nitrogen ions effectively increases the durability of cutting and stamping tools and the fatigue strength of parts.
Implantation of interstitial atoms (nitrogen, carbon and boron) improves the wear resistance and fatigue resistance of steels. These elements have the property of segregation to dislocations even at room temperature, which blocks their movement and strengthens the surface layer, and this in turn prevents the development of fatigue cracks.
When nickel is ion implanted with boron, fatigue strength increases by more than 100%.
The increase in fatigue strength is not due to the effect of residual compressive stresses arising during ion implantation, as previously thought, but to the inhibition of the development of fatigue cracks due to a decrease in dislocation mobility.
To increase anti-friction properties, molybdenum ions and double the amount of sulfur ions can be implanted. Joint implantation may become a new method for the formation of antifriction and other special alloyed layers.
By implanting titanium, an amorphous Ti-C-Fe phase is obtained on the surface, which leads to a reduction in friction and wear.
Ion implantation is widely used to improve the corrosion resistance of steel parts. For this purpose, ions are implanted.
Local heat treatment carries out modification of the structure of the surface layer. At the same time, such temperature-time regimes and hardening results are provided that are difficult or impossible to obtain using traditional heat treatment methods, namely:
High heating and cooling rates (heating rates reach values of 10 4 ... 10 8 K/s, and cooling rates - 10 3 ... 10 4 K/s, depending on the exposure time and radiation energy, as well as on laser operating modes ). Such heating and cooling modes lead to nonequilibrium phase transformations and a shift in critical points And with And A, the formation of supersaturated solid solutions with finely dispersed structures, including amorphous ones. As a result, a layer with increased hardness is formed (exceeds by 15 ... 20% the hardness after hardening using existing methods), with good resistance to wear and setting during friction;
Possibility of hardening surfaces in hard-to-reach places (cavities, recesses), where the laser beam can be introduced using optical devices;
The use of a laser allows one to sharply reduce the depth of the hardened layer and effectively control its size.
Laser hardening used to harden cutting and measuring tools, working edges of dies and punches to a depth of up to 0.15 mm (pulse radiation) and up to 1.5 mm (continuous radiation). On tool steels, the hardness is 63 ... 67 HRC. The roughness of the treated surface does not change.
It has been established that the use of laser radiation as a heating source during thermoplastic hardening of nickel alloys makes it possible to obtain residual compressive stresses of up to 10 GPa in the surface layer.
With laser heat treatment, it is possible to create conditions for the selective evaporation of asperity protrusions, which lead to a decrease in surface roughness.
Laser surfacing is one of the most promising methods for restoring critical parts of gas turbine engines, in particular turbine and compressor blades. Its main advantages are the ability to eliminate small defects without heating the surface adjacent to the defect and the absence of a delay during surfacing.
Laser surfacing is carried out in chambers with a protective atmosphere or with inert gas injection. Wire, foil or powder materials are used as filler materials.
Laser surfacing with powder metal alloys with minimal thermal effects makes it possible to increase the performance of parts several times under severe temperature, erosion and other operating conditions.
Ministry of Education and Science of the Russian Federation
Federal State Autonomous Educational Institution of Higher Professional Education "Ural Federal University named after the first President of Russia B.N. Yeltsin"
Department of Heat Treatment and Physics of Metals
"Classification of coatings according to functional properties and method of application"
Teacher:
Associate Professor, Ph.D. Rossina N.G.
Student: Trapeznikov A.I.
Group: Mt 320701
Ekaterinburg 2015
Introduction
Classification of coatings and methods of their production
1 Changes in the physical and chemical properties of surfaces during coating application
2 Interior coatings
3 External coatings
4 Surface preparation when applying coatings
Chemical and electrochemical coating methods
1 Classification of chemical and electrochemical coatings
2 The essence of the chemical coating method
3 Coating the product
Vacuum condensation coating
Application of surfacing coatings using concentrated heat sources
1 Classification of deposited coatings
2 Areas of application of surfacing
Application of coatings by cladding
Gas-thermal coating methods
1 Classifications of methods
Plasma spraying of coatings
1 Advantages and disadvantages of the plasma spraying method
Gas flame spraying of coatings
Conclusion
Introduction
The coatings available in modern technology are very diverse both in properties and methods of production. The use of protective, protective-decorative and special coatings allows solving many problems. By choosing the coating material, the conditions for their application, combining metallic and non-metallic coatings, it is possible to give the surface of products a different color and texture, the necessary physical, mechanical and chemical properties: increased hardness and wear resistance, high reflectivity, improved anti-friction properties, surface electrical conductivity, etc. . But the optimal choice of coatings or methods of finishing them is impossible without comprehensive consideration of their properties and production features.
Coating technology, along with other science-intensive and energy-saving industries, is one of the main directions for the development of modern production in advanced countries of the world community.
Currently, the improvement and search for new coating methods continues. Study of coating application methods, their varieties; thermodynamics of processes when creating coatings of various types on metal and non-metallic surfaces; structure, structure and performance properties of coatings; basic equipment for gas-thermal and electrothermal coating of metal products.
Studying methods for improving the quality of products by forming multilayer and reinforced coatings; metrological control of technological parameters of formation and their properties.
The role and place of coatings in modern production
Coatings are a single or multi-layer structure applied to a surface to protect against external influences (temperature, pressure, corrosion, erosion, etc.).
There are external and internal coatings.
External coatings have a boundary between the coating and the surface of the product. Accordingly, the size of the product increases by the thickness of the coating, and the weight of the product increases.
In internal coatings there is no interface and the dimensions and weight of the product remain unchanged, while the properties of the product change. Internal coatings are also called modifying coatings.
There are two main problems solved when applying coating
Changing the initial physical and chemical properties of the surface of products that provide specified operating conditions;
Restoration of properties, dimensions, weight of the surface of a product damaged by operating conditions.
Purpose and areas of application of coatings
The main reason for the emergence and development of technology for applying protective coatings was the desire to increase the durability of parts and assemblies of various mechanisms and machines. Optimization of a coating system involves appropriate selection of coating composition, structure, porosity and adhesion, taking into account both coating and operating temperatures, compatibility of substrate and coating materials, availability and cost of coating material, as well as the ability to renew, repair and properly maintain it. during operation.
The use of an insufficiently strong coating, the thickness of which noticeably decreases during operation, can lead to a decrease in the strength of the entire part due to a decrease in the effective area of its total cross-section. Mutual diffusion of components from the substrate to the coating and vice versa can lead to depletion or enrichment of alloys in one of the elements. Thermal exposure can change the microstructure of the substrate and cause residual stresses to appear in the coating. Taking into account all of the above, the optimal choice of a system should ensure its stability, i.e., the preservation of properties such as strength (in its various aspects), ductility, impact strength, fatigue and creep resistance after any impact. Operation under conditions of rapid thermal cycling has the strongest influence on the mechanical properties, and the most important parameter is the temperature and time of its exposure to the material; interaction with the surrounding working environment determines the nature and intensity of chemical exposure.
Mechanical methods of connecting the coating to the substrate often do not provide the required quality of adhesion. Much better results are usually obtained by diffusion joining methods. A good example of a successful diffusion coating is aluminizing ferrous and non-ferrous metals.
1. Classification of coatings and methods for their production
Currently, there are many different coatings and methods for their production.
Many publications propose various classification schemes for inorganic coatings based on various characteristics. Coatings can be classified according to the following basic principles:
By purpose (anti-corrosion or protective, heat-resistant, wear-resistant, anti-friction, reflective, decorative and others);
By physical or chemical properties (metallic, non-metallic, refractory, chemical-resistant, reflective, etc.);
By the nature of the elements (chrome, chrome-aluminum, chrome-silicon and others);
By the nature of the phases formed in the surface layer (aluminide, silicide, boride, carbide and others)
Let's look at the most important coatings, classified by purpose.
Protective coatings - the main purpose is associated with their various protective functions. Corrosion-resistant, heat-resistant and wear-resistant coatings have become widespread. Heat-protective, electrical insulating and reflective coatings are also widely used.
Structural coatings and films act as structural elements in products. They are also especially widely used in the production of products in instrument making, electronic equipment, integrated circuits, in turbojet engines - in the form of actuated seals in turbines and compressors, etc.
Technological coatings are intended to facilitate technological processes in the production of products. For example, applying solders when soldering complex structures; production of semi-finished products in the process of high-temperature deformation; welding of dissimilar materials, etc.
Decorative coatings are extremely widely used in the production of household products, decorations, improving the aesthetics of industrial installations and devices, prosthetics in medical equipment, etc.
Restorative coatings - provide a huge economic effect when restoring worn surfaces of products, such as propeller shafts in shipbuilding; crankshaft journals of internal combustion engines; blades in turbine engines; various cutting and pressing tools.
Optical coatings - reduce reflectivity compared to solid materials, mainly due to surface geometry. Profiling shows that the surface of some coatings is a collection of roughnesses, the height of which ranges from 8 to 15 microns. On individual macro-irregularities, micro-irregularities are formed, the height of which ranges from 0.1 to 2 microns. Thus, the height of the irregularities is commensurate with the wavelength of the incident radiation. Reflection of light from such a surface occurs in accordance with Frenkel's law.
In the literature there are various principles for classifying coating methods. Although it should be noted that there is no unified classification system for coating application methods. Hawking and a number of other researchers have proposed three classifications of coating methods:
According to the phase state of the medium from which the coating material is deposited;
According to the condition of the applied material;
According to the state of processes that define one group of methods
coating.
The classifications of coating methods are presented in more detail in Table 1.
Table 1 Advantages and disadvantages of various coating methods
MethodAdvantagesDisadvantagesPVDVersatility; All solid elements and materials can be deposited. It is possible to obtain thin films and fairly thick coatings. There are various modifications of the method. H = 5-260 microns. It is possible to apply coatings only to the visible part of the surface. Poor dissipation ability. Expensive equipment.CVDCompetes with physical deposition method. Elements and compounds that are chemically active and in a vapor state can be applied. Good dispersion ability. H = 5-260 µm. The heating source plays an important role. Deposition is usually carried out at higher temperatures than in the physical deposition method. The substrate may overheat. Undesirable direct deposition may occur. Diffusion deposition from solids Good uniformity and close dimensional tolerances of the coating. High economic efficiency of the process. The most common coating materials are Al and Cr. High hardness of the coating. H = 5 - 80 µm. Limited substrate dimensions. Not suitable for high temperature sensitive substrates. Thinner coatings than other diffusion methods. Possible embrittlement of coatings. Spraying Possibility of controlling spraying conditions and the quality of the applied material during the process. Possibility of obtaining thick, uniform coatings. H = 75 - 400 µm. Quality depends on the qualifications of the operator. The substrate must be resistant to heat and impact. The coatings are porous with a rough surface and possible inclusions. Cladding Thick coatings can be applied. Large substrates can be processed. H = 5 - 10% of the substrate thickness Possible warping of the substrate. Suitable for rigid substrates. Electrodeposition (including chemical and electrophoresis) Cost-effective process when using aqueous electrolytes. It is possible to apply precious metals and refractory coatings from molten salts. Used for industrial production of cermets. Chemical deposition and electrophoresis are only applicable for certain elements and types of substrates. H = 0.25 - 250 µm. Careful design of equipment is required to ensure good dissipation ability. The use of molten salts as electrolytes requires strict control to prevent moisture and oxidation. Harmful vapors above the melt. Coatings can be porous and stressed. Limited to special high temperature areas.Hot dippingRelatively thick coatings. Rapid coating method. H = 25 - 130 microns. Limited only by applying A1 to obtain high-temperature coatings. Coatings can be porous and discontinuous.
Table 2. Classification of coating methods according to the phase state of the medium
Solid stateMechanical bonding Cladding SinteringLiquid stateHot dipping Sputtering SurfacingSemi-liquid or paste stateSol-gel process Slip SolderingGas environment (atomic, ionic or electronic interaction)Physical vapor deposition Chemical vapor depositionSolutionChemical Galvanic ElectrogalvanicPlasmaSurface treatment
Table 3. Classification of coating methods according to the state of processes defining one group of methods
MechanicalClading CompoundPhysicalPhysical vapor deposition Vacuum coatings Thermal evaporation Sputtering Ion depositionChemicalChemical vapor deposition Deposition from an electrolyte without applying an electric fieldElectrochemicalIn aqueous solutions In molten saltsSputteringDetonation gun Electric arc Metallization Plasma Gas-flame using wire SurfacingLaser manual electric welding inert gas welding oxygen-acetylene welding in plasma arc Plasma welding Fusion by spraying Submerged arc Another between tungsten electrodes in an inert environment
Table 4. Classification of methods according to the state of the applied material and manufacturing methods
Group 1 Atomic or ionic stateVacuum methods: Vacuum evaporation Ion beam deposition Epitaxial molecular beam deposition Plasma methods: Sputtering (ionic, magnetron) Ion deposition Plasma polymerization Activated reaction evaporation Cathodic arc deposition Chemical interaction in reagent vapors: Vapor deposition Reduction Decomposition Plasma deposition Sputter pyrolysis Electrolyte deposition: Electroplating Chemical deposition Molten salt deposition Chemical substitutionGroup 2 ParticulatesImpact methods Fusion: Thick coating Enameling Electrophoresis Thermal methods: Flame atomization Plasma atomization Detonation atomization Sol-gel processGroup 3 Bulk materialExternal External coatings: Surfacing Cladding: Explosive rolling Laser melting Wetting: Brush painting Hot dipping Electrostatic methods: Spin coating Spray patterning Group 4 Surface structure modification Laser surface modification Heat treatment Ion implantation Surface alloying: Bulk diffusion Sputtering Leaching Chemical conversion liquid-vapor diffusion (heating, plasma) Electrolytic anodizing Thermal exchange working in molten salts Mechanical methods: Shot blasting
1.1 Changes in the physical and chemical properties of surfaces during coating application
The surface layer (coating) plays a decisive role in the formation of operational and other properties of products; its creation on the surface of a solid body almost always changes the physical and chemical properties in the desired direction. Application of coatings allows you to restore previously lost properties during the operation of products. However, most often the properties of the original surfaces of products obtained during their production are changed. In this case, the properties of the surface layer material differ significantly from the properties of the original surface. In the overwhelming majority, the chemical and phase composition of the newly created surface changes, resulting in products with the required performance characteristics, for example, high corrosion resistance, heat resistance, wear resistance and many other indicators.
Changing the physical and chemical properties of the original surfaces of products can be achieved by creating both internal and external coatings. Combined options are also possible (Fig. 1).
coating chemical vacuum cladding
When applying internal coatings, the dimensions of the products remain unchanged (L And = const). Some methods ensure that the mass of the product remains constant, while in other methods the increase in mass is negligible and can be neglected. As a rule, there is no clear boundary of the modified surface layer ( ?m ? const). When applying external coatings, the size of the product increases (L And ?const) on the coating thickness ( ?PC ). The weight of the product also increases. In practice, there are also combined coatings. For example, when applying heat-protective coatings characterized by an increased number of discontinuities in the outer layer, heat resistance is ensured due to the internal non-porous coating.
1.2 Internal coatings
Internal coatings are created by various methods of influencing the surface of the original material (modification of the original surfaces). In practice, the following methods of influence are widely used: mechanical, thermal, thermal diffusion and high-energy with penetrating flows of particles and radiation.
There are also combined methods of influence, for example thermomechanical, etc. In the surface layer, processes occur that lead to a structural change in the source material to a depth from the nanometer range to tenths of a millimeter or more.
Depending on the method of exposure, the following processes occur:
change in the grain structure of the material;
Distortion of the crystal lattice, change in its parameters and type;
destruction of the crystal lattice (amorphization);
changing the chemical composition and synthesizing new phases.
1.3 External coatings
The practical importance of external coatings is very great. The application of external coatings allows not only to solve problems of changing the physical and chemical properties of the original surfaces, but also to restore them after use.
The mechanism and kinetics of formation are shown in Fig. 3. External coatings often serve as a structural element, for example, coating films in the production of integrated circuits. To date, a large number of methods for applying coatings for various purposes from many inorganic materials have been developed.
To analyze the physicochemical processes associated with the application of coatings, it is advisable to systematize them according to the conditions of formation, it seems possible to distinguish the following groups of coatings formed on a solid surface: solid-phase, liquid-phase, powder and atomic.
1.4 Surface preparation when applying coatings
Surface preparation determines the main indicator of quality - the adhesion strength of the coating to the base material of the product, or adhesive strength. Some exceptions are coatings formed on a molten surface, for example, when surfacing coatings with concentrated heat sources. However, even in this case, contaminated surfaces negatively affect the properties of the coating material. Its embrittlement is observed, and the tendency to form defects increases: cracks, porosity, etc. In this regard, surface preparation is a key operation in the technological process of applying any coatings.
When preparing the surface, two important tasks must be solved:
) removal of adsorbed substances - contaminants - from the surface;
) surface activation.
Removal of contaminants and activation of the surface can be carried out either in a single technological process or separately. In principle, any removal of physically or chemically adsorbed substances from a surface already activates this surface.
Broken bonds of surface atoms and their asymmetry are restored and, accordingly, the level of surface energy increases. The greatest effect in surface preparation is achieved when, along with the removal of contaminants, the highest activation occurs. In real technological processes, such surface preparation is not always possible. Usually two or three-stage separate preparation is used. The final stage is mainly aimed at activating the surface to its maximum values.
In the practice of coating, the following basic methods of preparing the surface of products have been used: washing with cold or hot water; degreasing; etching; mechanical impact; thermal and chemical-thermal effects; electrophysical impact; exposure to light fluxes; dehydration.
2. Chemical and electrochemical coating methods
The production of coatings from solutions by chemical and electrochemical methods is a classic example of processes that make it possible to trace in a relatively pure manner the formation of applied layers by sequential addition of atoms to the surface of the coated product during its interaction with an ionic reaction medium.
There are standard definitions of methods for producing coatings made from aqueous solutions - electrolytes (GOST 9.008-82).
The chemical method of producing coatings is the production of a metallic or non-metallic inorganic coating in a salt solution without electric current from an external source. Examples of producing coatings by chemical methods are: for metal coatings obtained by reduction - nickel plating, copper plating, silver plating, etc.; for non-metallic coatings obtained by oxidation - oxidation, phosphating, chromating, etc. The latter are also used for additional processing of the coating.
The electrochemical method of obtaining a coating is the production of a metallic or non-metallic inorganic coating in an electrolyte under the influence of electric current from an external source.
Cathodic metal reduction is an electrochemical method for producing a metal coating on a metal that is the cathode.
Anodic oxidation is an electrochemical method for producing a non-metallic inorganic coating on a metal that is the anode.
Contact The method of obtaining a coating is to obtain a coating from a solution of salts of the applied metal by immersing the coated metal in contact with a more electronegative metal.
2.1 Classification of chemical and electrochemical coatings
Chemical and electrochemical coatings can be classified based on the following basic principles:
By production method (chemical, electrochemical, galvanic, cathodic, anodic-oxide and contact);
By type of material applied (metallic, non-metallic and composite);
According to the requirements for the coating (protective, protective-decorative, decorative, special);
In relation to the external chemically active environment (cathode, anodic, neutral);
According to the coating design (single-layer, multi-layer).
2.2 The essence of the chemical coating method
Coatings produced by chemical methods are characterized by lower porosity than those applied by galvanic methods at the same thickness and high uniformity.
Chemical deposition of metals is a reduction process that proceeds according to the equation:
Mez+ +Ze?M
where is Me z+ - metal ions present in solution; z - metal valency; Ze is the number of electrons; Me - metal coating.
Metal ions in solution (Me z+ ) combine (depending on valence) with the appropriate number of electrons (Ze) and turn into a metal (Me).
In the case of chemical deposition, the necessary electrons are generated as a result of a chemical process that occurs in the solution used to obtain the coating. In galvanic deposition, the electrons necessary for the reduction of metal ions are supplied by an external current source .Depending on the chemical process occurring during coating deposition, the following methods are distinguished.
Contact method (immersion), in which the metal to be coated is immersed in a solution containing a salt of a more electropositive metal, and the coating in this case is deposited due to the potential difference arising between the metal being coated and the ions in the solution. Contact-chemical method (internal electrolysis), in which deposition is carried out due to the potential difference that occurs when the metal being coated comes into contact with a more electronegative metal during immersion in a solution of the metal salt used for coating. A method of chemical reduction in which the metal to be coated is immersed in a solution containing a salt of the deposited metal, buffering and complexing additives and a reducing agent, while the ions of the deposited metal are reduced as a result of interaction with the reducing agent and deposited on the metal to be coated, and this reaction occurs only on the metal surface, being catalytic for this process.
2.3 Coating the product
The technological equipment used at domestic or foreign enterprises for the deposition of coatings by chemical reduction is designed based on specific production tasks: large parts are hung in baths using special devices, small parts are covered in bulk in drums, pipes (straight or coils) - in installations that provide the possibility of pumping solution through internal cavities, etc. Often, installations for chemical application are located in galvanic shops, which makes it possible to use the equipment available there for degreasing, insulating, pickling, washing, drying and heat treating parts.
A simplified diagram of the apparatus for applying chemical coatings is shown in Fig. 4.
Chemical coating is carried out in static or flow-through solutions. In some cases, the solution, after processing 1-2 batches of parts in it, is poured out and replaced with a fresh one; in others, the solution is filtered, adjusted, and used repeatedly. An installation for one-time coating of parts in a static solution usually has a welded iron or porcelain bath, which is inserted into a larger container - a thermostat. The space between the walls of both baths is filled with water or oil, which is heated with electric heaters or live steam. On the outside, the thermostat has a heat-insulating layer (for example, made of asbestos sheets, on which a casing is placed). A contact thermometer with a thermostat is placed in the bath to ensure maintenance of the required temperature of the working solution.
3. Vacuum condensation coating
There are many similarities in the methods and technological features of vacuum condensation coating (VCDC), and in this regard it is advisable to consider a generalized process diagram. A generalized diagram of the vacuum condensation coating process is shown in Fig. 5.
It is known that coatings during vacuum condensation deposition are formed from a stream of particles in an atomic, molecular or ionized state. Neutral and excited particles (atoms, molecules, clusters) with normal and high energy and ions with a wide energy range are transferred into coatings. The flow of particles is obtained by evaporation or atomization of the material by exposing it to various energy sources. Flows of particles of the applied material are obtained by the method of thermal evaporation, explosive evaporation - sputtering and ion sputtering of solid material. The application process is carried out in rigid sealed chambers at a pressure of 13.3 - 13.3 10-3Due to this, they provide the necessary free path of particles and protect the process from interaction with atmospheric gases. The transfer of particles towards the condensation surface occurs as a result of the difference in partial pressures of the vapor phase. The highest vapor pressure (13.3 Pa or more) near the spraying (evaporation) surface causes the movement of particles towards the surface of the product, where the vapor pressure is minimal. Other transport forces act in a flow of particles in an ionized state; ionized particles have more energy, which makes it easier to form coatings.
Vacuum condensation application methods are classified according to various criteria:
By methods of obtaining a vapor flow from the coating material and forming particles: thermal evaporation of the material from a solid or molten state, explosive (intensified) evaporation - spraying; ion sputtering of solid material;
According to the energy state of the particles: application by neutral particles (atoms, molecules) with different energy states; ionized particles, ionized accelerated particles (in real conditions, various particles are present in the flow);
According to the interaction of particles with residual gases of the chamber: application in an inert rarefied environment or high vacuum (13.3 MPa); and in an active rarefied environment (133 - 13.3 Pa).
The introduction of active gases into the chamber makes it possible to switch to the method of vacuum reaction coating. Particles in the flow or on the condensation surface enter into chemical interaction with active gases (oxygen, nitrogen, carbon monoxide, etc.) and form the corresponding compounds: oxides, nitrides, carbides, etc.
The classification of vacuum condensation coating is shown in Fig. 6. The choice of the method and its varieties (methods) is determined by the requirements for coatings, taking into account economic efficiency, productivity, ease of control, automation, etc. The most promising methods are vacuum condensation deposition with ionization of the flow of sprayed particles (plasma stimulation); These methods are often called ion plasma.
The following basic requirements apply to products produced by vacuum condensation methods:
Compliance with the size requirements of modern industry;
Low saturated vapor pressure of the product material at process temperature;
Possibility of heating the surface to increase the adhesive strength of coatings.
Vacuum condensation coating is widely used in various fields of technology. The vacuum reaction process creates wear-resistant coatings on products for various purposes: friction pairs, pressing and cutting tools, etc.
Vacuum condensation application makes it possible to obtain coatings with high physical and mechanical properties; from synthesized compounds (carbides, nitrides, oxides, etc.); thin and uniform; using a wide class of inorganic materials.
Technological processes associated with vacuum condensation deposition do not pollute the environment and do not disrupt the environment. In this respect, they compare favorably with chemical and electrochemical methods for applying thin coatings.
The disadvantages of the vacuum condensation deposition method include low productivity of the process (condensation rate of about 1 μm/min), increased complexity of technology and equipment, low energy coefficients of atomization, evaporation and condensation.
It is advisable to consider the process of vacuum condensation coating as consisting of three stages:
Transition of the condensed phase (solid or liquid) into gaseous (steam);
Formation of flow and transfer of particles to the condensation surface;
Condensation of vapors on the surface of the product - the formation of a coating.
To obtain high-quality coatings, flexible control of processes is necessary by creating optimal conditions for their occurrence.
4. Application of surfacing coatings using concentrated heat sources
The application of surfacing coatings using concentrated heat sources is carried out in the form of separate passes, each of which forms a bead of molten material of width b. Roller overlap ?b usually amounts to (1/4 - 1/3)3. The coating material consists of molten base material and filler material, which is fed into the bath. If the base material does not melt, then the weld bead is formed only from the filler material, in which case the share of the base material in the formation of the weld coating is zero. The most widely used surfacing methods are concentrated heat sources with slight melting of the base material of height h n . Height of the deposited layer bead h n usually 2 - 5 mm. When the rollers overlap, longitudinal grooves (irregularities) 1 - 2 mm deep are formed.
Knowing the chemical composition of the base and filler material and the proportion of their participation in the formation of the coating material, it is possible to determine the chemical composition of the deposited layer.
Under the influence of a concentrated heat source, the base material is locally heated, especially when it melts. The heat flow is transferred into the base material, forming a heat-affected zone (HAZ) in it. In the high-temperature HAZ region, as a rule, grain growth is observed, a hardened structure, and hot and cold cracks are formed. In practice, surfacing strives for the minimum length of the HAZ.
Under the influence of a heat source, the molten metal is displaced from the bath in separate portions, which, during the crystallization process, form a bead of deposited material. The crystallization process occurs on the basis of melted grains of the base material, the main axis of the crystallites is oriented in accordance with the direction of heat removal into the base material. During crystallization, the formation of defects is possible: hot and cold cracks, porosity, slag inclusions, etc. The nature of the formation of the coating from individual deposited beads (passes) with overlap does not allow obtaining thin and uniform deposits in thickness. A minimum coating thickness of 1 - 2 mm can only be achieved using precision technologies. Metallic materials are mainly used for surfacing coatings; sometimes various refractory non-metallic compounds are introduced into the molten metal.
4.1 Classification of deposited coatings
The classification of deposited coatings is carried out according to various criteria. It is most appropriate to classify by:
concentrated heat sources;
the nature of protection of the molten metal;
degree of mechanization.
Based on heat sources, surfacing coatings are divided into:
gas-flame;
plasma;
light beam;
electron beam;
induction;
electroslag.
According to the nature of the protection of the molten metal, they are distinguished: surfacing with slag, gas and gas-slag protection. According to the degree of mechanization, manual and mechanized surfacing will be replaced with automation elements.
4.2 Areas of application of surfacing
Surfacing with concentrated heat sources is used to restore worn surfaces; coatings, as a rule, provide a high economic effect. However, surfacing can also be used to create the initial surfaces of new products with a wide range of physical and chemical properties, for example, when creating exhaust valves in internal combustion engines, in the production of drilling tools, etc.
It is especially advisable to use surfacing to create wear-resistant surfaces in friction pairs, and minimal wear can be achieved due to both an increase in hardness in the deposited layer and a decrease in the friction coefficient. There is a known great economic effect when creating cutting tools. High-speed steel in a deposited coating was produced by argon-arc surfacing with the supply of filler wire from tungsten-molybdenum alloys with high carbon content (0.7 - 0.85 wt.%). For surfacing heavily loaded dies during hot stamping, coated electrodes were used, for example TsI-1M (type EN - 80V18Kh4F - 60, type F). Surfacing of wear-resistant coatings is widely used in the production of earth-moving equipment. In general, surfacing methods are highly effective; their disadvantages include:
greater thickness of the deposited layer (with some exceptions);
the presence of an extended heat-affected zone in the base material;
high surface roughness, which requires subsequent mechanical processing;
limited range of deposited materials, mainly metal.
5. Coating by cladding
Cladding includes a wide range of coating methods. These include:
Explosive percussion;
Magnetic impact;
Hot isostatic pressing, or cladding;
Obtaining a mechanical connection by extrusion.
With such a classification, cladding methods and methods with the formation of a diffusion bond overlap somewhat. Cladding methods are classified according to the speed of bond formation between the coating and the substrate:
1. Very fast processes (explosion cladding, electromagnetic impact);
Moderately fast processes (rolling, extrusion);
Slow processes (diffusion welding, hot isostatic pressing).
More commonly, cladding is used to coat ferrous alloys with nickel-based alloys. Cobalt cladding of steel is less common, mainly due to high costs.
Among the cladding methods, rolling and extrusion seem to be the most widely used methods. Production of coatings by explosion was discovered by accident in 1957. Hot isostatic pressing and production of coatings by electromagnetic impact are relatively new methods. Diffusion-coupled coatings were developed in the early 20th century to coat iron with nickel alloys and other high-temperature alloys for specialty applications.
6. Gas-thermal coating methods
Taking the type of heat source as the basis for the separation, the following spraying methods have been used in practice: plasma, gas-flame, detonation-gas, arc and high-frequency metallization.
The first gas-thermal coatings were obtained at the beginning of the 20th century. M.W. Schoop, who sprayed molten metal with a gas stream and, directing this flow to the base sample, obtained a coating layer on it. After the author's name, this process was called shopoping, and it was patented in Germany, Switzerland, France and England. The design of the first Schoop flame wire metallizer dates back to 1912, and the first electric arc wire metallizer - to 1918.
In domestic industry, gas-flame metallization has been used since the late 20s. At the end of the 30s it was successfully replaced by electric arc metallization. Equipment for electric arc metallization was created by N.V. Katz and E.M. Linnik.
Gas thermal spraying of coatings in world practice began to actively develop in the late 50s. This was facilitated by the creation of reliable technology for generating low-temperature plasma; detonation gas explosive devices, improvement of arc discharge processes.
Many scientific teams of the USSR Academy of Sciences, technical higher educational institutions, industry institutes and manufacturing enterprises were involved in the development of the theory, technology and equipment for thermal spraying. Work in the main leading foreign countries developed at a similar pace.
6.1 Method classifications
The methods and technology of thermal spraying have a lot in common. A diagram of the thermal spray process is shown in Fig. 7.
The sprayed material in the form of powder, wire (cords) or rods is fed into the heating zone. A distinction is made between radial and axial material feed. The heated particles are sprayed with gas, the main purpose of which is to accelerate the sprayed particles in the axial direction, but along with this it can also perform other functions. When feeding wire or rods into the heating zone, atomizing gas disperses the molten material; in a number of spraying methods it also performs the heating function.
The heating of particles, their atomization and acceleration by a gas flow predetermined the name of the process - thermal spraying. Particles arriving at the coating formation surface must ensure the formation of strong interatomic bonds during the contacting process, which requires their heating and an appropriate speed. It is known that the temperature of the particles determines thermal activation in the contact area; the speed of particles upon impact with the surface creates the conditions for mechanical activation of surface contact. It must be taken into account that at high particle velocities at the moment of their contact, part of the kinetic energy is converted into thermal energy, which also contributes to the development of thermal activation.
The developed methods of thermal spraying make it possible to regulate within sufficient limits the temperatures and speeds of particles arriving at the coating formation surface.
Thermal spraying methods are classified:
by type of energy;
by type of heat source;
by type of material sprayed;
by type of protection;
by the degree of mechanization and automation;
according to the periodicity of the particle flow.
Based on the type of energy, a distinction is made between methods using electrical energy (gas-electric methods) and methods in which thermal energy is generated by the combustion of flammable gases (gas-flame methods). To heat the sprayed material, the following types of heat sources are used: arc, plasma, high-frequency discharges and gas flame. Accordingly, the spraying methods are called: electric arc metallization, plasma spraying, high-frequency metallization, gas-flame spraying, detonation gas spraying. The first three methods are gas-electric, the last three are gas-flame.
Depending on the type of material being sprayed, powder, wire (rod) and combined spraying methods are used. In combined methods, flux-cored wire is used. The following spraying methods are known by type of protection: without process protection, with local protection and with general protection in sealed chambers. In general protection, a distinction is made between conducting the process at normal (atmospheric) pressure, at elevated pressure, and at vacuum (in low vacuum).
Degree of mechanization and automation of the process. With manual spraying methods, only the supply of the sprayed material is mechanized. Mechanized methods also provide for the movement of the sprayer relative to the sprayed product. The movement of sprayed products relative to a stationary sprayer is often used. The level of automation of spraying processes depends on the design of the installation; in the simplest versions there is no automation, but in complex complexes complete automation of the process is possible.
Flow frequency. Most spraying methods involve a continuous stream of particles. For some methods, only cyclic process management is possible. The coating is formed in a pulsed spraying mode, alternating with pauses. Gas thermal spraying methods are widely used for applying coatings for various purposes. The main advantages of thermal spraying methods include high productivity of the process with satisfactory quality of coatings.
7. Plasma spraying of coatings
The plasma jet is widely used as a source of heating, atomization and particle acceleration in coating deposition. Due to the high flow rate and temperature, the plasma jet allows the spraying of almost any material. A plasma jet is produced in various ways: by arc heating of gas; high-frequency induction heating, electric explosion, laser heating, etc.
A generalized diagram of the process of plasma spraying of coatings is shown in Fig. 8. With plasma spraying, both radial and axial supply of the sprayed material in the form of powder or wire (rods) is possible. Various types of plasma jets are used: turbulent, laminar, subsonic and supersonic, swirling and non-swirling, axisymmetric and plane-symmetric, continuous and pulsed, etc.
Laminar jets provide significantly larger values of the length of the outflowing flow (l n , l With ), due to which the heating time of the sprayed particles increases, and are characterized by higher values of the ratio of the supplied energy to the flow rate of the plasma-forming gas. Laminar jets should be classified as high-enthalpy jets. In addition, they are characterized by a high flow rate and a lower noise level (up to 40 - 30 dB). At present, solutions have not yet been found that allow the widespread use of laminar jets for spraying. The difficulties are mainly related to the supply of powder. The theory and practice of coating with laminar jets was developed by A. V. Petrov.
Supersonic plasma jets are also quite promising for spraying. High velocities of sprayed particles (800 - 1000 m/s or more) make it possible to form coatings mainly without melting them
The current level of plasma spraying is mainly based on the use of subsonic and supersonic, turbulent, axisymmetric, plasma jets with a wide range of thermophysical properties. About half of the power supplied to the atomizer is consumed to heat the plasma-forming gas. Typically, the thermal efficiency of the atomizer is 0.4-0.75. It should also be noted that the plasma jet is poorly used as a heat source for heating powder particles. Efficient efficiency of plasma heating of powder particles ?P is in the range of 0.01 - 0.15. When spraying wire, the effective efficiency is significantly higher and reaches 0.2 -0.3.
The most important thermophysical characteristics of plasma jets, which determine the optimal conditions for heating, atomization and acceleration of sprayed particles, include specific enthalpy, temperature and speed in various sections along the flow axis. Flexible control of the thermophysical parameters of the jet determines the manufacturability of the process and its capabilities.
According to the degree of protection of the process, plasma spraying is distinguished: without protection, with local protection and general protection.
7.1 Advantages and disadvantages of the plasma spraying method
The main advantages of the plasma spraying method:
high process productivity from 2 - 8 kg/h for plasma torches with a power of 20 - 60 kW to 50 - 80 kg/h with more powerful sprayers (150 - 200 kW);
versatility in the material being sprayed (wire, powder with different melting points;
a large number of parameters providing flexible control of the spraying process;
regulation within a wide range of the quality of sprayed coatings, including obtaining particularly high-quality process performance with general protection;
high CMM values (when spraying wire materials 0.7 - 0.85, powder materials - 0.2 - 0.8);
the possibility of complex mechanization and automation of the process;
wide availability of the method, sufficient efficiency and low cost of the simplest equipment.
The disadvantages of the method include:
low values of energy utilization factor (with wire spraying ?To = 0.02 - 0.18; powder - ?And = 0,001 - 0,02);
the presence of porosity and other types of discontinuities (2 - 15%);
relatively low adhesive and cohesive strength of the coating (maximum values are 80 - 100 MPa);
high noise level when the process is open (60 - 120 dB).
As the plasma spraying method improves, the number of disadvantages decreases. Promising, for example, are the developments of spraying with supersonic outflow of a plasma jet, which makes it possible to form coatings primarily from particles without melting that are in a viscoplastic state. Compared to the radial one, the axial supply of the sprayed material in arc plasma sprayers is most effective.
Plasma spraying using two-arc or three-phase plasma torches is of significant interest. The use of HF plasmatrons promises great advantages. In these cases, plasma is obtained that is not contaminated with electrode materials, and the axial supply of the sprayed material is simplified.
8. Gas flame spraying of coatings
A gas flame is produced by the combustion of combustible gases in oxygen or air. In special spray burners, a combustible mixture is supplied along the periphery of the nozzle, the central part is designed to supply the sprayed material into the formed gas-flame jet. Near the nozzle exit, the gas flame is a cone; as it moves away from the nozzle exit, the gas flame forms a continuous stream of high-temperature gas. There are laminar (R e < Rekp ) and turbulent jets (R e >R ECR ). The transition of the combustion mode and jet outflow from laminar to turbulent depends on the nature of the combustible gas and is determined by Reynolds numbers (Re = 2200 - 10000).
Gas-flame jets as a source of heating, atomization and acceleration during coating spraying are similar to plasma jets. However, the temperature, enthalpy and speed of the gas flame jet are much lower. Sprayed particles interact with a gas phase of complex composition, consisting of flammable gases, products of their combustion and dissociation, oxygen and nitrogen. The redox potential in the initial section of the jet is easily regulated by changing the ratio between the combustible gas and oxygen. Conventionally, three modes of flame formation can be distinguished: neutral, oxidative and reducing.
The following flammable gases are used for spraying coatings: acetylene (C 2N 2), methane (CH 4), propane (C 3N 8), butane (C 4H1 0), hydrogen (H 2) etc. Sometimes mixtures are used, for example propane-butane, etc.
Flame spraying is carried out in an open atmosphere. Air enters the gas flame, and therefore the amount of oxygen is greater than required for the complete oxidation of the elements of the combustible gas according to the above reactions. To balance the compositions, reduce the amount of oxygen in the combustible gas - oxygen mixture.
The highest flame temperature is achieved when using acetylene-oxygen mixtures. However, the heating value is higher for propane and butane. Therefore, standard technical acetylene or a propane-butane mixture is most often used for spraying. When gas-plasma jets are formed, the thermal efficiency of the atomizer is quite high ( ?t.r. = 0.8 - 0.9). In this case, most of the supplied energy is spent on heating the gas. However, the effective heating efficiency of powder particles ( ?And ) composition is only 0.01 - 0.15.
1 Methods of flame spraying
A general diagram of the flame spraying process is shown in Fig. 9.
Combustible gas and oxygen (rarely air) enters the mixing chamber 3, the combustible mixture then enters the nozzle device 7, at the exit from it the mixture is ignited and forms a flame torch 2. To compress the gas flame, an additional nozzle 4 is used, into which compressed gas is supplied, usually air or nitrogen. The external co-current gas stream 5 lengthens the high-temperature gas stream, increases its temperature, enthalpy and speed; in addition, the gas can be used to cool the heat-stressed elements of the atomizer.
The sprayed material in the form of powder or wire (rods) is fed along the axis of the gas-flame jet into the torch, which promotes more intense heating and atomization of the material.
Flame spraying methods are classified according to the following criteria:
Type of material being sprayed. A distinction is made between flame spraying using powder and wire (rod) materials.
Type of flammable gas. There are known methods of spraying using acetylene or gases that are substitutes for acetylene (propane, butane, their mixtures, etc.).
Degree of mechanization. Manual spraying and mechanized (machine) spraying are used. With manual methods, only the supply of sprayed material is mechanized. Fully mechanized methods provide for the movement of the sprayed product relative to the sprayer or vice versa and introduce automation elements.
2 Installations for gas flame spraying
Our country produces a number of installations for flame spraying of wire and powder materials. Acetylene and propane-butane mixture are used as energy gases. Acetylene (or substitute), oxygen, and in some cases additional gas (air) for spraying are supplied to the sprayer from the gas supply unit. The gas supply unit is not included in the manufactured device. It is mounted directly on the work site. Apparatuses for flame spraying are usually equipped with a spray gun (gun), a wire or powder feed mechanism and a control panel. Often the wire feed mechanism is located in the same housing as the spray gun, on which the powder feeder is mounted.
Conclusion
Modern production, taking into account modern achievements of science and technology, requires the creation of a powerful base for the implementation of new methods of applying coatings from various groups of inorganic materials. Coatings with a wide range of physical and chemical properties are required: for protection in various environments; wear-resistant; optical; heat-protective and many others. Significant efforts are also required to improve existing and long-used coating methods.
To solve these problems, it is necessary to use an integrated approach associated not only with solving specific scientific and technical aspects of creating new technologies in the field of coatings, but also the task of optimization and coordinated storage and dissemination of information is becoming increasingly important.
List of used literature
1. Grilikhes, S.Ya., Tikhonov, K.I. Electrolytic and chemical coatings. L.: Chemistry, 1990. -288 p.
Kovensky, I.M., Povetkin, V.V. Methods for studying electrolytic coatings. -M.: Nauka, 1994. -234 p.
Molchanov V.F. Combined electrolytic coatings - Kyiv: Tekhnika, 1976. -176 p.
Dasoyan, M.A., Palmskaya, I.Ya., Sakharova, E.V. Electrochemical coating technology. -L.: Mechanical Engineering, 1989. -391 p.
Eichis, A.P. Coatings and technical aesthetics. -Kiev: Technology, 1971. - 248 p.
Biront, V.S. Coatings: a textbook for university students. - Krasnoyarsk. GATSMIZ, 1994. - 160 p.
Bobrov, G.V. Application of inorganic coatings (theory, technology, equipment): a textbook for university students. / G.V. Bobrov, A.A. Ilyin. - M.: Intermet Engineering, 2004. - 624 p.
8. Lainer, V.I. Protective coatings for metals / V.I. Liner, - M.: Metallurgy, 1974. - 560 p.
9.. Nikandrova, L.I. Chemical methods for producing metal coatings./ L.I. Nikandrova. - L.: Mechanical Engineering, 1971. 101 p.
Corrosion: Reference publication. / Ed. L.L. Schreyer. - M.: Metallurgy. 1981. - 632 p.
Chemical-thermal processing of metals and alloys: Handbook / Ed. L.S. Lyakhovich. M.: Metallurgy, 1981.-.424 p.
Kolomytsev, P.T. Heat-resistant diffusion coatings / P.T. Kolomytsev. - M.: Metallurgy, 1979. - 272 p.
Hawking, M. Metal and ceramic coatings / M. Hawking, V. Vasantasri, P. Sidki. - M.: Mir, 2000. - 516 p.
Owners of patent RU 2265075:
The invention relates to the field of metallurgy, namely to methods for treating the surfaces of conductive materials. A method has been proposed for modifying the surface of conductive bodies by heating it with an alternating electric current, while current pulses with a duration of 20-100 ns and an amplitude providing a surface melting depth of 1-10 μm are used to modify the surface. The technical result is the development of a method for modifying the surface of conductive bodies to improve the performance characteristics of metals and alloys and control the required properties, such as hardness, wear resistance, fatigue and corrosion resistance. 3 ill.
The invention relates to the field of processing electrically conductive materials by heating with an electric field.
State of the art
Many physical and mechanical properties of materials strongly depend on the state of the surface. For example, hardness, fatigue, wear, corrosion strength and crack resistance are significantly improved by reducing the grain size and amorphizing the surface layer. There are a large number of ways to influence a surface in order to harden it. Such methods include cladding and the application of various coatings, laser and mechanical processing (for example, sandblasting), ion implantation, and so on. Using rapid quenching methods, amorphous and nanocrystalline materials of certain chemical compositions are obtained from the melt. The critical cooling rate required for amorphization and the glass transition temperature depend on the nature of the chemical composition of the melt. Typical quenching rates for amorphizing systems are 10 5 -10 7 K/sec and are achieved using melt spinning methods - jet cooling on a massive rotating block, melt rolling between cold rollers, spraying a melt jet with gas flows (gas atomization).
Using these methods, either powders or flakes with characteristic sizes of 1-100 nm, or thin ribbons with a thickness of 10-100 microns are obtained. Amorphization of pure metals requires extremely high cooling rates -10 12 -10 14 K/sec, which are unattainable with modern rapid hardening schemes. Slower quenching rates of 10 2 -10 4 - K/sec are used to produce so-called massive metal glasses with characteristic dimensions of the order of several millimeters in cross-section. Such glasses are obtained from melts with a wide region of supercooling, the presence or absence of which is determined by the chemical composition of the alloy. Small sizes, high cost and limited amorphizing compositions during high-speed hardening limit the areas of application of amorphous alloys. The advantages of surface treatment of finished products are obvious. For example, the ion implantation method is used to amorphize the surface layer by bombarding with high-energy ions (for example, bombarding nickel with P + ions at room temperature - dose 10 17 ions/cm 2, ion energy 40 keV - leads to the formation of an amorphous phase in the surface layer) .
The method of laser amorphization of a surface is well known, which uses a powerful pulsed laser beam that scans over the surface and melts small areas of the surface layer, which, after the cessation of laser radiation, quickly harden due to intense heat removal into the massive substrate. For more efficient amorphization, amorph-forming elements are introduced into the composition of the processed material. Technological disadvantages of laser amorphization are the complexity of the equipment, high cost and relatively low speed of processing large surfaces. The metallurgical disadvantages of this method include high internal stresses formed at the boundary of the amorphized layer and the crystalline matrix, and, most importantly, high macro- and micro-inhomogeneity of the structure caused by scanning the laser beam over the surface being processed.
Another method of heat treatment of both the entire volume and the surface layers of the material, chosen as a prototype, is induction heating - heating of conductive bodies by exciting electric currents in them by an alternating electromagnetic field. To create the latter, currents of low (50 Hz), medium (up to 10 kHz) and high (over 10 kHz) frequencies are used. Used for melting metals, surface hardening of parts, etc.
The attractiveness of induction heating in industry is associated, first of all, with technological simplicity, high productivity, high accuracy of maintaining the heat treatment regime, a high degree of environmental friendliness, and ease of integration into automated production lines. Currently, induction heating equipment has been developed and manufactured for a variety of industrial applications:
For volumetric and surface heat treatment of metal products for the purpose of hardening, normalization, improvement, annealing, tempering, chemical-thermal treatment;
For heating metal workpieces before plastic deformation;
For heating the surfaces of metal products for special purposes.
The power of modern installations for induction heating of metal is tens - hundreds of kW, operating frequencies - units of kHz - units - MHz.
The essence of the invention
The essence of the invention is the use of powerful short electrical pulses to modify the surface of electrically conductive objects.
1. improving the performance characteristics of metals and alloys;
2. control of required properties, such as hardness, wear resistance, fatigue, corrosion resistance;
3. reducing production costs;
a method is proposed for modifying the surface structure by forming amorphous, nano- and microcrystalline surface layers. Unlike the prototype, we propose to use a powerful single current pulse, leading to the required heating of the surface (skin layer).
The skin effect consists of localizing a high-frequency electric current in a thin near-surface layer of a conductor. Skin layer thickness δ is estimated as:
where ω is the frequency of alternating current, μ is the magnetic permeability and σ is the conductivity of the conductor. When a current pulse of duration t 0 with density j flows through a conductor with resistivity ρ=1/σ, heat q is released:
This heat is spent on increasing the internal energy and, consequently, the temperature of the surface skin layer, since the pulse duration is short and changes in the structure and heat outflow through the outer surface can be neglected. The temperature increment ΔT over a short time interval t 0 is proportional to the amount of heat q:
where c v is the specific heat capacity and ρ m is the density of the conductive layer.
For estimations, we will assume that the shape of a current pulse of duration t 0 is close to the half-cycle of a sinusoidal function with frequency ω. Then we can assume:
Let current I flow through a cylindrical sample of radius R 0 . Then the cross-sectional area S of the skin layer with thickness δ will be:
Then we can find the relationship between the total current I and the current density j:
Substituting (1, 2, 4-6) into (3), we obtain an estimate of the dependence of the surface heating value on the current amplitude I and the sample radius R0:
Substituting (4) into (1), we obtain expressions for determining the required duration of the electric pulse to modify the surface layer with thickness δ:
From (7) we can find the current amplitude required to heat the surface of a sample of radius R 0 by the value ΔT:
Thus, expressions (8, 9) make it possible to estimate the parameters of the current pulse required to heat a surface layer of thickness δ to temperature ΔT.
The cooling time t f of the surface layer is determined by the diffusion of heat into the sample and depends on its thickness (δ) and the thermal diffusivity coefficient α.
where λ is the thermal conductivity coefficient.
The most important characteristic of surface treatment, which determines, in particular, the appearance of an amorphous surface layer, is its cooling rate T:
Using (8, 10), we get:
Thus, as follows from the expressions obtained, short, powerful current pulses are required to achieve the melting temperature of the skin layer and obtain a high cooling rate. Estimates show that to process samples with a diameter of the order of millimeters and obtain a cooling rate of the order of 10 10 K/s, current pulses with an amplitude of about 100 kA and a duration of tens of nanoseconds are required.
The required structure and thickness of the modified layer can be adjusted by controlling the amount of melt overheating or the temperature of the surface layer in the event that surface melting is not desired, and the cooling rate, which in turn is determined by the amplitude, duration of the applied current pulse and the initial temperature of the sample. Consequently, the proposed method realizes the advantages of surface heat treatment and high-speed hardening.
The implementation of the proposed method depends on the technical capabilities of obtaining short current pulses of large amplitude. The main problem is to ensure a high speed of energy output from the generator to the load. Currently, for the best capacitors with an energy capacity of ˜10 4 J, this time is ˜300 ns. The time it takes to remove energy from the battery is determined both by the parameters of the capacitors themselves and by the load. Adding an external load leads to an inevitable increase in the system inductance and an increase in the energy output time to ˜1 μs.
Currently, the highest energy output rates are obtained in two-stage generators, which include a primary current pulse generator (CPG) and a power augmentation system (PAS). GIN is usually a battery of pulse capacitors, connected according to one or another circuit (for example, Marx circuit) and powered from a high voltage source. The power increase system is designed to significantly (10-100 times) increase the energy density coming from the GIN to produce a current pulse with a duration of ˜(10-100) ns on the load. There are two types of SMS - based on an intermediate capacitive storage device or using an inductive storage device. The energy density in inductive storage devices is tens of times higher than in capacitive storage devices. However, they require the use of high-current, high-speed current circuit breakers that switch the generator to the load, which represents a serious scientific and technical problem.
SMAs based on a single (or double) coaxial-type forming line filled with glycerol (relative dielectric constant ε=44) or deionized water (ε=81) are easier to implement. In these environments, it is possible to obtain a sufficiently high value of the electric field strength for the duration of the charge, and therefore (taking into account the rather large value of the high-frequency dielectric constant ε), and a high energy density, which ensures the receipt of a short and powerful electric pulse.
The purpose of the invention is to modify the surface of electrically conductive objects.
This goal is achieved by the fact that in the method of modifying conductive bodies by exciting an electric current in them with an alternating electromagnetic field, what is new is that powerful single current pulses of a nanosecond duration range are used to modify the surface.
Due to the fact that methods of surface modification based on the use of nanosecond high-power current pulses are unknown in the prior art, it meets the “novelty” criterion.
Due to the fact that the claimed invention does not obviously follow from analogues and prototypes, it meets the criterion of “inventive step”.
As will be shown below, due to the high calculated value of the cooling rate and the expected relatively low specific cost, the scope of industrial application of the claimed invention can be very wide. Accordingly, the claimed invention meets the criterion of “industrial applicability”.
List of drawing figures
Figure 1 shows the results of calculating the passage of a current pulse with an amplitude of 240 kA and a duration of 40 ns through a copper cylindrical sample with a diameter of 1 mm. Graphs of the time dependence of the current strength - I, flowing through the sample, the temperature of the sample surface - T, the radius of the phase transition (melting) - R m and the rate of temperature change from the moment of melting - dT/dt are presented.
Figure 2 shows a micrograph of the surface of a copper cylindrical sample with a length of 10 mm and a diameter of 0.8 mm, processed by a current pulse according to the claimed method. The surface image was obtained using a Hitachi S-3500 scanning electron microscope.
Figure 3 shows micrographs of the same section of the surface of a cylindrical sample of nitinol (NuTi) with a diameter of 1.0 mm, treated with a current pulse according to the claimed method. Figure 3a shows the surface of the sample in its original state. and in Fig. 3b - after processing. The surface image was obtained using a Hitachi S-3500 scanning electron microscope.
Information confirming the possibility of implementing the invention.
For surface modification of metals, current pulse generators (CPGs) with a nanosecond duration of 20...100 ns and a current amplitude of ˜100 kA can be used. As a rule, such generators are made on the basis of single (double) forming lines (FL) of the coaxial type, filled with glycerol or deionized water. The use of these lines in GIT designs is due to the following factors:
1. The duration of the current pulse is determined by the electrical length of the PL and can easily be changed by using either additional PL segments or PL of different electrical lengths.
2. The rise time of the current pulse in the generator significantly depends on the inductance of the discharge circuit, mainly determined by the short-circuiting spark gap and, to a large extent, the height of the latter. When installing a multi-channel short-circuit arrester with a current through each channel of ˜10 kA in the line instead of a single-channel one, it is possible to reduce the duration of the current pulse rise.
3. In the event of an electrical breakdown in the line, the liquid dielectric does not lose its electrical strength properties and can be used in the future.
As an example of implementation, we present the results of calculations performed for a copper cylinder with a diameter of 1 mm, initial temperature T 0 = 300 K. The parameters of the current pulse were chosen in such a way as to ensure a melting depth of ˜1÷10 μm.
It was found that for a copper sample with a current pulse amplitude I = 240 kA and its duration t 0 = 40 ns, the thickness of the fused layer was 9 μm. The heating process lasted ˜0.1 μs, the cooling process lasted ˜1 μs. The maximum heating reached 1953 K (at the melting and evaporation temperatures of copper 1356 K and 2868 K, respectively). The maximum cooling rate was T=1.8·10 11 K/s.
The calculation results are confirmed experimentally, as shown in Fig. 2 for a copper sample with a diameter of 0.8 mm, and in Fig. 3 for a sample of nylon with a diameter of 1 mm, which were processed according to the claimed method. Melting of the surface layer is obvious.
Thus, based on the proposed method, it is possible to develop industrial installations that provide heat treatment to the surface of products.
Information sources
1. Surface Engineering, Euromat-99, Vol. 11, ed. H.Dimigen, Willey-VCH, Germany (2000) 539 rub.
2. V.P. Alekhin, V.A. Khonik, Structure and physical patterns of deformation of amorphous alloys. M.: Metallurgy, 1992, 248 p.
3. A.I.Manokhin, B.S.Mitin, V.A.Vasiliev, A.V.Revyakin, Amorphous alloys. M.: Metallurgy, 1992, 160 p.
4. E.M. Breinan, Phys.Today V.29 (1976) pp. 45-51.
5. A. Inoue, Bulk Amorphous Alloys, Practical Characteristics and Applications, Trans.Tech.Pub., Swizerland(1999) 146p.
7. I. R. Pashby, S. Bames and B. G. Bryden, Surface hardening of steel using a high power diode laser. Journal of Materials Processing Technology, 139 (2003) pp.585-588.
8. G. W. Stachowiak and A. W. Batchelor, Surface hardening and deposition of coatings on metals by a mobile source of localized electrical resistive heating. Journal of Materials Processing Technology, 57 (1996) pp.288-297.
Coating allows you to solve two technological problems. First consists of directional change in the physical and chemical properties of the original surfaces of products, providing specified operating conditions, second- V restoration of the properties of product surfaces, violated by operating conditions, including loss of size and weight. The use of coatings can significantly improve the performance characteristics of products: wear resistance, corrosion resistance, heat resistance, heat resistance, etc.
Currently, the improvement and search for new coating methods continues.
Study of coating methods and their varieties; thermodynamics of processes when creating coatings of various types on metal and non-metallic surfaces; structure, structure and performance properties of coatings; basic equipment for gas-thermal and electrothermal coating of metal products.
Studying methods for improving the quality of products by forming multilayer and reinforced coatings; metrological control of technological parameters of formation and their properties.
The role and place of coatings in modern production
Coatings- This single or multi-layer structure applied to the surface to protect against external influences(temperature, pressure, corrosion, erosion and so on).
There are external and internal coatings.
External coatings have a boundary between the coating and the surface of the product. Respectively the size of the product increases with the thickness of the coating, At the same time, the mass of the product increases.
In internal coatings there is no interface and dimensions and the mass of the product remain unchanged, while the properties of the product change. Internal coatings are also called modifying coatings.
There are two main problems solved when applying coating
1. Change in the initial physical and chemical properties of the surface of products that provide specified operating conditions;
2. Restoration of the properties, dimensions, mass of the surface of the product, violated by operating conditions.
Purpose and areas of application of coatings
The main reason for the emergence and development of protective coating technology was the desire to increase the durability of parts and assemblies of various mechanisms and machines. Optimization of the coating system involves appropriate choice of coating composition, its structure, porosity and adhesion, taking into account both the coating temperature, so operating temperature, compatibility of substrate and coating materials, availability and cost of the coating material, as well as the possibility of its renewal, repair and proper care during operation
The use of an insufficiently durable coating, the thickness of which noticeably decreases during operation, can lead to a decrease in the strength of the entire part due to a decrease in the effective area of its total cross-section. Mutual diffusion of components from the substrate into the coating and vice versa can lead to depletion or enrichment alloys one of the elements. Thermal impact Maybe change microstructure substrate and call appearance of residual stresses in the coating. Taking into account all of the above, the optimal choice of a system should ensure its stability, i.e., the preservation of properties such as strength (in its various aspects), ductility, impact strength, fatigue and creep resistance after any impact. Operation under conditions of rapid thermal cycling has the strongest influence on mechanical properties, and the most important parameter is temperature and time of its exposure to the material; interaction with the surrounding working environment determines the nature and intensity of chemical exposure.
Mechanical methods of connecting the coating to the substrate often do not provide the required quality of adhesion. Much better results are usually obtained by diffusion joining methods. A good example of a successful diffusion coating is aluminizing ferrous and non-ferrous metals.
Classification of coatings and methods of their production
Currently, there are many different coatings and methods for their production.
In many publications Various schemes for classifying inorganic coatings according to various criteria are proposed.
Coverage can be classified according to the following basic principles:
1. By purpose(anti-corrosion or protective, heat-resistant, wear-resistant, anti-friction, reflective, decorative and others);
2. By physical or chemical properties(metallic, non-metallic, refractory, chemical-resistant, reflective, etc.);
3. By the nature of the elements(chrome, chrome-aluminum, chrome-silicon and others);
4. By the nature of the phases formed in the surface layer(aluminide, silicide, boride, carbide and others)
Let's look at the most important coatings, classified by purpose.
Protective coatings– the main purpose is related to their various protective functions. Corrosion-resistant, heat-resistant and wear-resistant coatings have become widespread. Heat-protective, electrical insulating and reflective coatings are also widely used.
Structural coatings and films– perform a role structural elements in products. They are also especially widely used in the production of products in instrument making, electronic equipment, integrated circuits, in turbojet engines - in the form of actuated seals in turbines and compressors, etc.
Technological coatings- intended to facilitate technological processes in the production of products. For example, applying solders when soldering complex structures; production of semi-finished products in the process of high-temperature deformation; welding of dissimilar materials, etc.
Decorative coatings– are extremely widely used in the production of household products, jewelry, improving the aesthetics of industrial installations and devices, prosthetics in medical equipment, etc.
Restorative coatings– give huge economic effect when restoring worn surfaces of products, for example propeller shafts in shipbuilding; crankshaft journals of internal combustion engines; blades in turbine engines; various cutting and pressing tools.
Optical coatings– reduce reflectivity compared to solid materials, mainly due to the surface geometry. Profiling shows that the surface of some coatings is a collection of roughnesses, the height of which ranges from 8 to 15 microns. On individual macro-irregularities, micro-irregularities are formed, the height of which ranges from 0.1 to 2 microns. Thus, the height of the irregularities is commensurate with the wavelength of the incident radiation.
Reflection of light from such a surface occurs in accordance with Frenkel's law.
In the literature there are various principles for classifying coating methods. Although It should be noted that there is no unified classification system for coating application methods.
Hawking and a number of other researchers have proposed three classifications of coating methods:
1. According to the phase state of the medium, from which the coating material is deposited;
2. According to the condition of the applied material;
3. By process status, which define one group of coating methods.
More detailed classifications of coating methods are presented in Table 1.1
Advantages and disadvantages of various coating methods presented in the table
Table 1.1
Table 1.2
Classification of coating methods according to the phase state of the medium.
Table 1.3
Classification of coating methods according to the state of processes defining one group of methods
Table 1.4
Classification of methods according to the state of the applied material and manufacturing methods
Changes in the physical and chemical properties of surfaces during coating application
The surface layer (coating) plays a decisive role in the formation of operational and other properties products, creating it on the surface of a solid almost always changes the physical and chemical properties in the desired direction. Coating allows you to restore previously lost properties during product operation.. However, most often the properties of the original surfaces of products obtained during their production are changed. In this case, the properties of the surface layer material differ significantly from the properties of the original surface. In the overwhelming majority, the chemical and phase composition of the newly created surface changes, resulting in products with the required performance characteristics, for example, high corrosion resistance, heat resistance, wear resistance and many other indicators.
Changes in the physical and chemical properties of the original surfaces products can be achieved by creating both internal and external coatings. Combination options are also possible(Fig. 1.1).
When applying internal coatings, the dimensions of the products remain unchanged (L And = const). Some methods also ensure constant mass of the product., in other methods - the mass increase is negligible and can be neglected. Usually, there is no clear boundary of the modified surface layer(δм ≠ const).
When applying external coatings product size increases (L and ≠ const) on the coating thickness (δpc). The weight of the product also increases.
N 
In practice, there are also combined coatings. For example, when applying heat-protective coatings characterized by an increased number of discontinuities in the outer layer,
heat resistance is ensured by an internal non-porous coating.
Rice. 1.1. Schematic representation of changes in the physicochemical properties of surfaces ( Li – original product size; δ m – depth of the inner layer; δ pc – coating thickness; σ a – adhesion strength of the coating; δ к – cohesive strength; P – discontinuities (pores, etc.); О Н – residual stresses)
Internal coatings
Internal coatings are created by various methods of influencing the surface of the source material(modification of original surfaces). In practice, the following methods of influence are widely used: mechanical, thermal, thermal diffusion and high-energy with penetrating flows of particles and radiation (Fig. 1.2).
Meet and combined methods of influence, for example, thermomechanical, etc. In the surface layer, processes occur that lead to a structural change in the source material to a depth from the nanometer range to tenths of a millimeter or more. Depending on the method of influence the following processes take place:
– change in the grain structure of the material;
– lattice distortion, changing its parameters and type;
– destruction of the crystal lattice(amorphization);
– changing the chemical composition and synthesizing new phases.
Rice. 1.2. Scheme of surface modification by various influences ( R-pressure; T- temperature; WITH– diffusing element; J– flow energy; τ – time)
External coatings
The practical importance of external coatings is very great. The application of external coatings allows not only to solve problems of changing the physical and chemical properties of the original surfaces, but also restore them after use.
The mechanism and kinetics of formation are shown in Fig. 1.3. External coatings often act as a structural element, for example, coatings - films in the production of integrated circuits. To date, a large number of methods for applying coatings for various purposes from many inorganic materials have been developed.
Rice. 1.3. Schemes for the formation of coatings on a solid surface
For the analysis of physical and chemical processes related to coating, their it is advisable to systematize according to the conditions of formation. It seems possible to distinguish the following groups of coatings formed on a solid surface: solid-phase, liquid-phase, powder and atomic.
Control questions:
1. Define the term coverage.
2. What are the two main tasks that are solved when applying coatings?
3. Name the main purpose and areas of application of coatings.
4. Name the main criteria by which coatings are classified.
5. What coatings are called protective?
6. Name the main criteria for classifying coating application methods.
7. Name the main groups of methods classified according to the state of the applied material.
8. How do the physicochemical properties of the surface change when coatings are applied?
9. Name the main differences between internal and external coatings.
10. Give an example of combined coatings.
Lecture 2. Physicochemical properties of solid surfaces
INTRODUCTION
Processes for modifying the surfaces of conductive materials are widely used to create special properties of various products in optics, electronics, and also as a finishing treatment for a wide range of products for household and technical purposes. Existing mechanical polishing methods are labor-intensive, complex and often lead to undesirable structural changes in the surface layer of products and the creation of additional stresses, which can be crucial in the formation of thin films with special properties in microelectronics. Widely used electrochemical methods for polishing metal products are expensive, mainly due to the use of expensive acidic electrolytes, which also cause great environmental damage to the environment. In this regard, the greatest importance is attached to the development and implementation of new technological processes that allow maintaining the quality and structure of the surface, have high productivity and good environmental and economic performance. Such processes include polishing of various conductive materials using the electrolyte-plasma method. Unlike traditional electrochemical polishing in acids, electrolyte-plasma technology uses environmentally friendly aqueous solutions of low concentration salts (3–6%), which are several times cheaper than toxic acid components.
No special treatment facilities are required for the disposal of spent electrolytes. The polishing time is 2–5 minutes, and the deburring time is 5–20 seconds. This method allows you to process products in four main areas:
- surface preparation before applying thin films and coatings;
- polishing complex-profile surfaces of critical parts;
- removing burrs and dulling sharp edges;
- decorative polishing of metal products;
Currently, electrolytic plasma processing of various steels and copper alloys is used at a number of enterprises in Belarus, Russia, Ukraine, as well as in China and other countries. The widespread use of this technology is hampered by the limited range of polished materials and products, since electrolytes and polishing modes for products with complex shapes and metals such as aluminum and titanium, as well as semiconductor materials, have not been developed. The search for effective electrolytes requires a more in-depth study of the mechanism for removing roughness and the formation of surface gloss during electrolyte-plasma action on conductive materials.
PHYSICAL-CHEMICAL PROCESSES UNDER ELECTROLYTE-PLASMA INFLUENCE
The operation of electrolyte-plasma processing installations is based on the principle of using pulsed electrical discharges that occur along the entire surface of the product immersed in the electrolyte. The combined effect of a chemically active environment and electrical discharges on the surface of a part creates the effect of polishing products. In electrolytic plasma polishing technology, the workpiece is an anode, to which a positive potential is supplied, and a negative potential is supplied to the working bath. After exceeding certain critical values of current and voltage densities, a vapor-plasma shell is formed around the metal anode, pushing the electrolyte away from the metal surface. The phenomena occurring in the near-electrode region do not fit into the framework of classical electrochemistry, since a multiphase metal-plasma-gas-electrolyte system arises near the anode, in which ions and electrons serve as charge carriers /3/.
Polishing of metals occurs in the voltage range of 200–350 V and current densities of 0.2–0.5 A/cm 2 /2.3/. At a voltage of more than 200 V, a stable thin (50–100 μm) vapor-plasma shell (VPC) is formed around the anode, characterized by small current fluctuations at U = const. The electric field strength in the shell reaches 10 4 –10 5 V/cm 2 . At a temperature of about 100 0 C, such a voltage can cause ionization of vapors, as well as the emission of ions and electrons necessary to maintain a stationary glowing electric discharge in the near-electrode shell. Near the microprotrusions, the electric field strength increases significantly and pulsed spark discharges occur in these areas with the release of thermal energy.
Research has established that the stability and continuity of the PPO, being a necessary condition for the implementation of the process of smoothing micro-irregularities, are determined by a set of various physical and chemical parameters: electrical characteristics of the circuit, thermal and structural conditions on the surface being processed, chemical and phase composition of the material being processed, molecular properties of the electrolyte and hydrodynamic parameters liquids in the near-electrode region /1–4/.
ADVANTAGES OF ELECTROLYTE-PLASMA TREATMENT
In the Republic of Belarus, for the first time, a new high-performance and environmentally friendly method of electrolyte-plasma processing of metal products from stainless steel and copper alloys in aqueous salt solutions has found industrial application. This method is largely devoid of the disadvantages that are inherent in mechanical and electrochemical polishing, and additionally allows saving material and financial resources. Electrolyte-plasma technology has higher technical characteristics of the process, such as the processing speed of the product, the class of its surface cleanliness, the absence of the introduction of abrasive particles and degreasing of the surface. The process can be fully automated; large production areas are not required to accommodate the equipment (Fig. 1).
Figure 1. Installation diagram for polishing conductive products. 1 - working bath; 2 - electric pump; 3 - preparatory bath; 4 - transformer; 5 - electrical cabinet; 6 - control panel.
The use of more high-performance methods of electrolytic plasma polishing will replace labor-intensive mechanical and toxic electrochemical processing. The process of polishing metals is environmentally friendly and meets sanitary standards; special treatment facilities are not required to clean the spent electrolyte.
The main technical solutions for electrolyte-plasma polishing technology for a number of metals have been developed and patented in Germany and Belarus. Known electrolytes are suitable for processing a limited class of metals and do not polish aluminum, titanium, etc. The Institute of Energy Problems of the National Academy of Sciences of Belarus (now the Joint Institute of Energy and Nuclear Research - Sosny of the National Academy of Sciences of Belarus) has developed a new composition of electrolytes for polishing deformable aluminum alloys, which does not contain concentrated acids, is not aggressive towards equipment, is durable and has low cost, an application for the invention was filed on May 20, 2002.
ECONOMIC INDICATORS OF ELECTROLYTE-PLASMA TREATMENT
When polishing 1 m 2 of a product using the classical electrochemical method, about 2.5 kg of acids costing 3 USD are consumed, and when polishing using the electrolyte-plasma method, about 0.1 kg of salts costing 0.02 USD are consumed. Calculations show that with two-shift operation of electrolyte-plasma equipment for 200 days, the saving of financial resources per year is about 30,000 USD, thus, with an installation cost of 26,000 USD. its payback does not exceed one year. In addition, this calculation does not take into account the savings obtained due to the lack of costs for treatment facilities.
In addition to the fact that electrolyte-plasma technology has higher productivity and is environmentally friendly, it has better economic performance compared to mechanical and electrochemical processing methods. Although the energy consumption during electrolytic plasma polishing (operating voltage is 220-320 V) is significantly higher than when processing with the traditional electrochemical method at low voltages, nevertheless, the total operating costs when using this technology are on average six times lower and this economic the gain is achieved primarily by replacing the expensive acid electrolyte with a cheap aqueous solution of salts. It should be noted that to obtain the polishing effect, reagents (salts) of high chemical purity are not required, which has a very significant impact on their cost. The economic indicators of electrolyte-plasma technology are also noticeably improved by a simplified scheme for recycling spent electrolyte and the absence of special treatment facilities.
Cost calculations when using the technology under consideration show that with an increase in installation capacity, when the maximum area of the polished surface per load increases, the total unit costs (per 1 m2 of surface) decrease, including the reduction of capital and operating cost components separately. In this case, there is a shared redistribution of costs among individual expense items. The data given is valid for continuous seven-hour operation of the installation per shift for twenty working days per month. The practice of using the proposed method shows that, depending on the size, shape, volume of the batch of processed products and the operating mode of the installation, you should select the appropriate power of the installation that gives the lowest costs and the shortest payback period.
PROSPECTS FOR ELECTROLYTE-PLASMA PROCESSING OF CURRENT CONDUCTING MATERIALS
The Joint Institute for Energy and Nuclear Research - Sosny of the National Academy of Sciences of Belarus (JIPNR-Sosny) is conducting research on the development of effective electrolytes for polishing a wide range of conductive materials and products, work is underway to develop technology, create and implement equipment. Theoretical and experimental studies are aimed at optimizing the process taking into account thermophysical factors, such as the boiling crisis, as well as the physical parameters of the electrolyte (surface tension coefficient, viscosity, contact angle) in order to develop scientifically based approaches to searching for electrolyte compositions that provide a given processing quality a wide range of materials with minimal expenditure of resources used (material, energy, time, labor, etc.).
JIPINR-Sosny NASB has developed a power range of equipment EIP-I, EIP-II, EIP-III, EIP-IV for polishing stainless steels and copper alloys using the electrolyte-plasma method, costing from 4000 USD. up to 22000 USD various capacities from 400 cm 2 to 11000 cm 2 per load. These products are export-oriented. Such installations have been supplied to many Belarusian, Russian and Ukrainian enterprises. In the manufacture of electrolytic plasma equipment, materials and components manufactured in Belarus are used.
In order to further save energy, a new economical power source and a two-stage polishing method have been developed using high operating voltages in the first stage of removing surface roughness and carrying out the second final stage of processing in an electrolyte at lower voltages. The energy-saving effect of equipping installations with a new power source and using a two-stage polishing mode for conductive products can amount to from 40 to 60% of the consumed electricity compared to the standard power sources used at a constant fixed voltage.
CONCLUSIONS
The most significant factors influencing the technological regime of electrolyte-plasma processing of conductive materials have been identified. It is shown that the new method of processing in electrolyte has a number of technical and economic advantages compared to existing technologies for polishing surfaces of a wide range of products.
The widespread adoption of environmentally friendly methods of processing conductive materials in various industries will not only save material and labor resources and dramatically increase labor productivity in metalworking, but also solve a significant social problem of significantly improving the working conditions of engineering and technical personnel and creating a more favorable environmental situation at enterprises and in the regions.
LITERATURE
- Patent No. 238074 (GDR).
- I.S.Kulikov, S.V.Vashchenko, V.I.Vasilevsky Features of electric-pulse polishing of metals in electrolyte plasma // VESCI NSA ser. Phys.-tech. Sci. 1995. No. 4. pp. 93–98.
- B.R. Lazarenko, V.N. Duraji, Bryantsev I.V. On the structure and resistance of the near-electrode zone when heating metals in electrolyte plasma // Electronic processing of materials. 1980. No. 2. pp. 50–55.
- Patent of the Republic of Belarus No. 984 1995.
Kulikov I.S., Vashchenko S.V., Kamenev A.Ya.