Ion-plasma nitriding as one of the modern methods of surface hardening of materials. Ion-plasma nitriding type Ion-plasma nitriding unit

13.05.2020

20.01.2008

Ion-plasma nitriding (IPA)- this is a kind of chemical-thermal treatment of machine parts, tools, stamping and casting equipment, providing diffusion saturation of the surface layer of steel (cast iron) with nitrogen or nitrogen and carbon in nitrogen-hydrogen plasma at a temperature of 450-600 ° C, as well as titanium or titanium alloys at temperature 800-950 °C in nitrogen plasma.

The essence of ion-plasma nitriding is that in a nitrogen-containing gas medium discharged to 200-000 Pa between the cathode, on which the workpieces are located, and the anode, the role of which is played by the walls of the vacuum chamber, an abnormal glow discharge is excited, forming an active medium (ions, atoms, excited molecules). This ensures the formation of a nitrided layer on the surface of the product, consisting of an external nitride zone with a diffusion zone located under it.

By varying the composition of the saturating gas, pressure, temperature, holding time, it is possible to obtain layers of a given structure with the required phase composition, providing strictly regulated properties of steels, cast irons, titanium or its alloys. Optimization of the properties of the hardened surface is provided by the necessary combination of nitride and diffusion layers that grow into the base material. Depending on the chemical composition, the nitride layer is either a y-phase (Fe4N) or an e-phase (Fe2-3N). The e-nitride layer is corrosion resistant and the y-layer is wear resistant but relatively ductile.

At the same time, with the help of ion-plasma nitriding, it is possible to obtain:

diffusion layer with a developed nitride zone, providing high corrosion resistance and running-in of rubbing surfaces - for wear parts

diffusion layer without nitride zone - for cutting, stamping tools or parts operating under high pressures with alternating loads.

Ion-plasma nitriding can improve the following characteristics of products:

wear resistance

fatigue endurance

extreme pressure properties

heat resistance

corrosion resistance

The main advantage of the method is stable quality of processing with a minimum dispersion of properties from detail to detail, cage to cage. In comparison with the widely used methods of hardening chemical-thermal treatment of steel parts, such as carburizing, carbonitriding, cyanidation, gas nitriding, the ion-plasma nitriding method has the following main advantages:

higher surface hardness of nitrided parts

no deformation of parts after processing

increase in endurance limit with increase in wear resistance of machined parts

lower process temperature, resulting in no structural changes to the workpieces

Possibility of processing blind and through holes

preservation of the hardness of the nitrided layer after heating to 600 - 650 ° C

the possibility of obtaining layers of a given composition

the ability to process products of unlimited sizes of any shape

no pollution environment

improving the culture of production

reducing the cost of processing several times

The advantages of ion-plasma nitriding are manifested in a significant reduction in the main production costs. For example, compared to gas nitriding, IPA provides:

reduction of processing time from 2 to 5 times, both by reducing the time of heating - cooling of the charge, and by reducing the time of isothermal exposure

reduction in the consumption of working gases (20 - 100 times)

reduction in electricity consumption (1.5 - 3 times)

reduced deformation enough to eliminate finish grinding

improvement of sanitary and hygienic conditions of production

full compliance of the technology with all modern requirements for environmental protection

Compared to hardening, processing by ion-plasma nitriding allows:

exclude deformations

increase the service life of the nitrided surface (2-5 times)

The use of ion-plasma nitriding instead of carburizing, nitrocarburizing, gas or liquid nitriding, bulk or high-frequency hardening allows:

save capital equipment and production space

reduce machine costs, transport costs

reduce the consumption of electricity, active gaseous media.

The main consumers of equipment for ion-plasma nitriding are automotive, tractor, aircraft, shipbuilding, ship repair, machine / machine tool plants, plants for the production of agricultural machinery, pumping and compressor equipment, gears, bearings, aluminum profiles, power plants ...

The method of ion-plasma nitriding is one of the most dynamically developing areas of chemical-thermal treatment in industrialized countries. The IPA method has found wide application in the automotive industry. It is successfully used by the world's leading auto / engine building enterprises: Daimler Chrysler (Mercedes), Audi, Volkswagen, Voith, Volvo.
For example, the following products are processed by this method:

nozzles for cars, automatic drive carrier plates, dies, punches, dies, molds (Daimler Chrysler)

springs for injection system (Opel)

crankshafts (Audi)

camshafts (Volkswagen)

compressor crankshafts (Atlas, USA and Wabco, Germany)

gears for BMW (Handl, Germany)

bus gears (Voith)

hardening of pressing tools in the production of aluminum products (Nughovens, Scandex, John Davis, etc.)

There is a positive experience of industrial use this method CIS countries: Belarus - MZKT, MAZ, BelAZ; Russia - AvtoVAZ, KamAZ, MMPP Salyut, Ufa Engine Building Association (UMPO).
The IPA method processes:

gears (MZKT)

gears and other parts (MAZ)

large (more than 800 mm) diameter gears (BelAZ)

intake and exhaust valves (AvtoVAZ)

crankshafts (KamAZ)

As the world experience in the application of ion-plasma nitriding technology shows, the economic effect of its implementation is ensured mainly by reducing the consumption of electricity, working gases, reducing the labor intensity of manufacturing products due to a significant reduction in the volume of grinding work, and improving product quality.

With regard to cutting and stamping tools, the economic effect is achieved by reducing its consumption due to an increase in its wear resistance by 4 or more times with a simultaneous increase in cutting conditions.

For some products, ion-plasma nitriding is the only way to obtain a finished product with a minimum percentage of rejects.

In addition, the IPA process ensures complete environmental safety.

Ion-plasma nitriding can be used in production instead of liquid or gas nitriding, carburizing, nitrocarburizing, high-frequency hardening.

Improving the properties of a metal can take place by changing its chemical composition. An example is the nitriding of steel - relatively new technology saturation of the surface layer with nitrogen, which began to be used on an industrial scale about a century ago. The technology under consideration was proposed to improve some of the qualities of products made from steel. Let us consider in more detail how steel is saturated with nitrogen.

Appointment of nitriding

Many people compare carburizing and nitriding because both are designed to dramatically increase the performance of a part. The nitrogen injection technology has several advantages over carburizing, among which there is no need to increase the billet temperature to the values at which the attachment of the atomic lattice takes place. It is also noted that the nitrogen application technology practically does not change the linear dimensions of the blanks, due to which it can be used after finishing. On many production lines, parts that have been quenched and ground are nitrided, almost ready for production, but some qualities need to be improved.

The purpose of nitriding is associated with a change in the main performance characteristics in the process of heating the part in an environment characterized by a high concentration of ammonia. Due to such an impact, the surface layer is saturated with nitrogen, and the part acquires the following operational qualities:

The wear resistance of the surface is significantly increased due to the increased hardness index.
The value of endurance and resistance to the growth of fatigue of the metal structure are improved.
In many industries, the use of nitriding is associated with the need to impart anti-corrosion resistance, which is maintained in contact with water, steam or air with high humidity.

The above information determines that the results of nitriding are more significant than carburizing. The advantages and disadvantages of the process largely depend on the chosen technology. In most cases, the transferred performance is maintained even when the workpiece is heated to a temperature of 600 degrees Celsius, in the case of cementing, the surface layer loses hardness and strength after heating to 225 degrees Celsius.

Technology of the nitriding process

In many ways, the steel nitriding process is superior to other methods that involve changing the chemical composition of the metal. Nitriding technology for steel parts has the following features:

In most cases, the procedure is carried out at a temperature of about 600 degrees Celsius. The part is placed in a sealed iron muffle furnace, which is placed in the furnace.
Considering the modes of nitriding, one should take into account the temperature and holding time. For different steels, these indicators will differ significantly. Also, the choice depends on what performance needs to be achieved.
Ammonia is supplied from a cylinder into the created metal container. The high temperature causes the ammonia to decompose, releasing nitrogen molecules.
Nitrogen molecules penetrate the metal due to the passage of the diffusion process. Due to this, nitrides are actively formed on the surface, which are characterized by increased resistance to mechanical stress.
The procedure of chemical-thermal exposure in this case does not provide for sudden cooling. As a rule, the nitriding furnace is cooled along with the ammonia flow and the part, so that the surface does not oxidize. Therefore, the technology under consideration is suitable for changing the properties of parts that have already been finished.

The classical process of obtaining the required product with nitriding involves several stages:

Preparatory heat treatment, which consists of hardening and tempering. Due to the rearrangement of the atomic lattice under a given regime, the structure becomes more viscous, and strength increases. Cooling can take place in water or oil, another medium - it all depends on how high quality the product should be.
Next, machining is performed to give the desired shape and size.
In some cases, there is a need to protect certain parts of the product. Protection is carried out by applying liquid glass or tin with a layer about 0.015 mm thick. Due to this, a protective film is formed on the surface.
Nitriding of steel is carried out according to one of the most suitable methods.
Work is underway on finishing machining, removing the protective layer.

The resulting layer after nitriding, which is represented by nitride, is from 0.3 to 0.6 mm, thereby eliminating the need for a hardening procedure. As previously noted, nitriding is carried out relatively recently, but the process of transforming the surface layer of the metal has already been almost completely studied, which has made it possible to significantly increase the efficiency of the technology used.

Metals and alloys subjected to nitriding

There are certain requirements that apply to metals before carrying out the procedure in question. As a rule, attention is paid to the concentration of carbon. The types of steels suitable for nitriding are very different, the main condition is the proportion of carbon 0.3-0.5%. Best results achieved with the use of alloyed alloys, since additional impurities contribute to the formation of additional solid nitrites. An example of the chemical treatment of metal is the saturation of the surface layer of alloys that contain impurities in the form of aluminum, chromium, and others. The alloys under consideration are commonly referred to as nitralloys.

The introduction of nitrogen is carried out when using the following steel grades:

If a significant mechanical effect is exerted on the part during operation, then the 38X2MYUA brand is chosen. It contains aluminum, which causes a decrease in deformation resistance.
In the machine tool industry, 40X and 40XFA steels are most widely used.
In the manufacture of shafts, which are often subjected to bending loads, grades 38KhGM and 30KhZM are used.
If during manufacturing it is necessary to obtain high accuracy of linear dimensions, for example, when creating parts of fuel units, then the steel grade 30KhZMF1 is used. In order to significantly increase the strength of the surface and its hardness, alloying with flint is preliminarily carried out.

When choosing the most suitable steel grade, the main thing is to observe the condition associated with the percentage of carbon, and also take into account the concentration of impurities, which also have a significant impact on the performance properties of the metal.

The main types of nitriding

There are several technologies by which steel nitriding is carried out. Let's take the following list as an example:

Ammonia-propane environment. Gas nitriding has become very widespread today. In this case, the mixture is represented by a combination of ammonia and propane, which are taken in a ratio of 1 to 1. As practice shows, gas nitriding when using such a medium requires heating to a temperature of 570 degrees Celsius and holding for 3 hours. The resulting layer of nitrides is characterized by a small thickness, but at the same time, wear resistance and hardness are much higher than with the use of classical technology. Nitriding of steel parts in this case makes it possible to increase the hardness of the metal surface to 600-1100 HV.
Glow discharge is a technique that also involves the use of a nitrogen-containing environment. Its peculiarity lies in the connection of nitrided parts to the cathode, the muffle acts as a positive charge. By connecting the cathode, it is possible to speed up the process several times.
The liquid medium is used a little less often, but is also characterized by high efficiency. An example is a technology that involves the use of a molten cyanide layer. Heating is carried out to a temperature of 600 degrees, the exposure period is from 30 minutes to 3 hours.

In industry, the most widespread is the gaseous medium due to the possibility of processing a large batch at once.

Catalytic gas nitriding

This type of chemical treatment involves the creation of a special atmosphere in the oven. Dissociated ammonia is pre-treated on a special catalytic element, which significantly increases the amount of ionized radicals. The features of the technology are as follows:

Preliminary preparation of ammonia makes it possible to increase the proportion of solid solution diffusion, which reduces the proportion of reaction chemical processes during the transition of the active substance from the environment to iron.
Provides for the use of special equipment that provides the most favorable conditions chemical processing.

This method has been used for several decades, it allows you to change the properties of not only metals, but also titanium alloys. The high costs of installing equipment and preparing the environment determine the applicability of the technology to obtaining critical parts that must have accurate dimensions and increased wear resistance.

Properties of nitrided metal surfaces

Quite important is the question of what hardness of the nitrided layer is achieved. When considering hardness, the type of steel being processed is taken into account:

Carbon steel can have hardness within 200-250HV.
Alloyed alloys after nitriding acquire hardness in the range of 600-800HV.
Nitralloys, which contain aluminum, chromium and other metals, can get hardness up to 1200HV.

Other properties of the steel also change. For example, the corrosion resistance of steel increases, due to which it can be used in an aggressive environment. The process of introducing nitrogen itself does not lead to the appearance of defects, since heating is carried out to a temperature that does not change the atomic lattice.

And industrially developed productions today give preference to chemical-thermal treatment, in particular, ion-plasma nitriding (hereinafter referred to as IPA), which compares favorably with thermal technologies from an economic point of view. Today, IPA is actively used in machine, ship and machine tool building, agricultural and repair industries, for the production of energy industry installations. Among the enterprises that actively use the technology of ion-plasma nitriding are such big names as the German concern Daimler Chrysler, the automobile giant BMW, the Swedish Volvo, the Belarusian plant of wheeled tractors, KamAZ and BelAZ. In addition, the advantage of IPA was appreciated by the manufacturers of pressing tools: Skandex, Nughovens.

Process Technology

Ion-plasma nitriding, used for working tools, machine parts, equipment for stamping and casting, ensures the saturation of the surface layer of the product with nitrogen or a nitrogen-carbon mixture (depending on the material of the workpiece). IPA plants operate in a rarefied atmosphere at pressures up to 1000 Pa. The chamber, which operates on the principle of a cathode-anode system, is supplied with a nitrogen-hydrogen mixture for processing cast iron and various steels, or pure nitrogen as a working gas for working with titanium and its alloys. The workpiece serves as the cathode, and the chamber walls serve as the anode. The excitation of an abnormally glowing charge initiates the formation of a plasma and, as a consequence, an active medium, which includes charged ions, atoms and molecules of the working mixture that are in an excited state. Low pressure provides a uniform and complete coating of the workpiece with a glow. The plasma temperature ranges from 400 to 950 degrees, depending on the working gas.

For ion-plasma nitriding, 2-3 times less electricity is required, and the quality of the surface of the processed product makes it possible to completely eliminate the stage of finishing grinding

The film formed on the surface consists of two layers: the lower diffusion layer and the upper nitride layer. The quality of the modified surface layer and economic efficiency The process as a whole depends on a number of factors, including the composition of the working gas, the temperature and the duration of the process.

Ensuring a stable temperature rests on the heat exchange processes occurring directly inside the IPA chamber. To reduce the intensity of metabolic processes with the walls of the chamber, special non-conductive heat shields are used. They allow significant savings in power consumption. The temperature of the process, coupled with the duration, affects the depth of penetration of nitrides, which causes changes in the graph of the depth distribution of hardness indicators. Temperatures below 500 degrees are the most optimal for nitriding cold-worked alloy steels and martensitic materials, since performance is increased without changing the hardness of the core and thermal destruction of the internal structure.
The composition of the active medium affects the final hardness and size of the nitride zone and depends on the composition of the workpiece.

Results of the application of ion-plasma nitriding

Ion-plasma nitriding makes it possible to increase wear resistance indicators with a simultaneous decrease in the tendency to fatigue damage to the metal structure. Obtaining the required surface properties is determined by the ratio of the depth and composition of the diffusion and nitride layers. The nitride layer, based on the chemical composition, is usually divided into two defining phases: "gamma" with a high percentage of Fe4N compounds and "upsilon" with Fe2N Fe3N. -phase is characterized by low plasticity of the surface layer with high resistance to various types of corrosion, ε-phase gives a relatively plastic wear-resistant coating.

As for the diffusion layer, the adjacent developed nitride zone reduces the likelihood of intergranular corrosion, providing a roughness grade sufficient for active friction. Parts with such a ratio of layers are successfully used in wear mechanisms. The exclusion of the nitride layer makes it possible to prevent destruction with a constant change in the load force under conditions of sufficiently high pressure.

That. ion-plasma nitriding is used to optimize wear, heat and corrosion resistance with a change in fatigue endurance and roughness, which affects the likelihood of scuffing of the surface layer.

Advantages of ion plasma nitriding

Ion-plasma nitriding in a well-adjusted technical process gives a minimum spread of surface properties from part to part at a relatively low energy intensity, which makes IPA more attractive than traditional furnace gas nitriding, nitrocarburizing and cyanidation.

Ion-plasma nitriding eliminates workpiece deformation, and the structure of the nitrided layer remains unchanged even when the part is heated to 650 degrees, which, coupled with the possibility of fine adjustment of physical and mechanical properties, makes it possible to use IPA for solving a wide variety of problems. In addition, ion-plasma nitriding is excellent for processing steels of various grades, since working temperature process in the nitrogen-carbon mixture does not exceed 600 degrees, which excludes violations of the internal structure and, on the contrary, helps to reduce the likelihood of fatigue damage and damage due to the high brittleness of the nitride phase.

To improve anticorrosion performance and surface hardness by ion-plasma nitriding, workpieces of any shape and size with through and blind holes are suitable. Screen protection against nitriding is not a complex engineering solution, so the processing of individual sections of any shape is easy and simple.

Compared to other methods of hardening and increasing the intergranular resistance, IPA is characterized by a several times shorter duration of the process and a two-fold reduction in the consumption of working gas. That. ion-plasma nitriding requires 2-3 times less electricity, and the quality of the surface of the processed product makes it possible to completely eliminate the stage of finishing grinding. In addition, it is possible to reverse the nitriding process, for example before grinding.

Epilogue

Unfortunately, against the background of even neighboring countries, domestic manufacturers use nitriding by the ion-plasma method quite rarely, although the economic and physical and mechanical advantages are visible to the naked eye. The introduction of ion-plasma nitriding into production improves working conditions, increases productivity and reduces the cost of work, while the service life of the processed product increases by 5 times. As a rule, the issue of building technical processes using installations for IPA rests on the problem financial plan, although there are no subjectively real obstacles. Ion-plasma nitriding, with a fairly simple equipment design, performs several operations at once, the implementation of which by other methods is possible only in stages, when the cost and duration will creep up sharply. In addition, there are several companies in Russia and Belarus cooperating with foreign manufacturers of IPA equipment, which makes the purchase of such units more affordable and cheaper. Apparently, the main problem lies only in the banal decision-making, which, as a Russian tradition, will be born in our country for a long time and difficult.

With the right composition and mode of application of wear-resistant coatings, the performance of the cutting tool can be significantly improved. However, due to the invariability of the properties of the coating within one layer at the interface with the tool base, the physical, mechanical and thermal properties (primarily the modulus of elasticity and thermal expansion coefficient) change dramatically, which leads to the formation of high residual stresses in the coating and a decrease in the strength of its adhesive bond. with a base, which is the most important condition for the successful operation of a coated cutting tool.

The specified, as well as changes in contact and thermal processes during processing with a coated tool, require the creation of an intermediate transitional layer between the tool base and the coating, which increases the resistance of the coated cutting wedge to acting loads.

The most common method for forming such a layer is ion nitriding. In this case, the nitrided layer formed before coating, depending on the specific operating conditions of the tool, must have a certain structure, thickness, and microhardness. In practice, high-speed steel tools are usually subjected to such processing.

Figure 4. Schematic diagram of a vacuum-arc installation for combined tool processing, including ion nitriding and coating: 1 - target; 2 - anode; 3 - screen; 4 - vacuum chamber; 5 - neutral atoms; 6 - ions; 7 - electrons; 8 - processed tools

For ion nitriding and subsequent coating, it is advisable to use an installation based on a vacuum-arc discharge, in which all stages of combined hardening can be implemented in one technological cycle without overloading the processed tools.

The principle of operation of such an installation is as follows (Figure 4).

The target is evaporated by cathode spots of the vacuum arc and is used as an arc discharge cathode. A special screen located between the target and the anode divides the chamber into two zones filled with metal-gas (to the left of the screen) and gas plasma (to the right). This screen is impervious to microdroplets, neutral atoms and metal ions emitted by cathode spots on the target surface. Only electrons penetrate the screen, ionize the gas supplied to the chamber on their way to the anode, and in this way form a gas plasma that does not contain metal particles.

The tools immersed in the plasma are heated by electrons when a positive potential is applied to them, and when a negative potential is applied, they are nitrided. At the end of nitriding, the screen is shifted to the side, and after the particles of the metal target begin to flow onto the surface of the tool, the coating is synthesized.

Coating deposition is a very energy-intensive process, accompanied by the action of a high-energy plasma flow, especially at the time of ion bombardment. As a result, the characteristics of the layer obtained by ion nitriding can change significantly.

Therefore, when optimizing the process of combined processing of high-speed tools, it is necessary to take into account factors not only of the nitriding process, but also of the subsequent process of applying a wear-resistant coating - first of all, the application time, on which the coating thickness directly depends. On the one hand, its increase has a positive effect on increasing the wear resistance of the contact pads of the tool, and on the other hand, it leads to a noticeable increase in the number of defects in the coating, a decrease in the adhesion strength of the coating to the tool material, and a decrease in the ability of the coating to resist elastic-plastic deformations.

The most important conditions for combined treatment are the temperature and duration of the nitriding process, the volume fraction of nitrogen in the gas mixture with argon, and the time of the subsequent wear-resistant coating process. Other factors this process: nitrogen pressure, reference voltage, arc current on the cathode - mainly affect the characteristics of the coating and should be set the same as in the case of the deposition of traditional coatings.

Depending on the type of cutting tool and the conditions of its subsequent operation during combined processing, its modes usually vary within the following limits: nitriding temperature 420 ... 510 ° C; atomic fraction of nitrogen N 2 in a gas mixture with argon 10 ... 80%; nitriding time 10...70 min; gas mixture pressure ~ 9.75·10 -1 Pa; coating application time 40...80 min.

The practice of operating tools made of high-speed steels after combined hardening in various machining operations shows that the presence of a nitrided layer under the coating, in which there is a brittle nitride zone (?- and?-phase), significantly limits the effect of combined processing.

Such a structure is formed during nitriding in an atmosphere of pure nitrogen using a vacuum-arc discharge plasma. The presence of a relatively thick nitride zone (> 0.5 µm) in continuous cutting (turning and drilling) does not provide a significant increase in tool life compared to a tool with a traditional coating, and in interrupted cutting (milling and chiselling) often leads to chipping of cutting edges already in the first minutes of operation of the tool.

The introduction of argon into the composition of a nitrogen-containing atmosphere during nitriding prior to coating deposition makes it possible to control the phase composition of the formed layer and, depending on the specific operating conditions of the cutting tool and its service purpose, obtain the necessary structure.

When operating a high-speed tool with combined machining under intermittent cutting conditions, the optimal structure of the nitrided layer is a viscous and load-resistant solid solution of nitrogen in martensite, in which the formation of a small amount of dispersed nitrides of alloying components is permissible.

This structure can be obtained by nitriding in a medium containing ~ 30% N 2 and 70% Ar.

In the case of tool operation in continuous cutting conditions, the layer consisting of nitrogenous martensite and special nitrides of alloying elements (W, Mo, Cr, V) is characterized by the highest performance.

In addition, the presence of a very small amount of ?-phase is admissible. This structure increases the resistance of the surface layer of the tool to thermal loads and can be formed during nitriding in a medium containing ~ 60% N2 and 40% Ar.

The (Ti, Al)N coating deposited on samples nitrided in one-time mixtures containing, %, 60 N 2 + 40 Ar and 30 N 2 + 70 Ar, is characterized by a satisfactory adhesion strength. The samples do not show any peeling of the coating, nor obvious cracks, which were found on samples nitrided at 100% N 2 .

The creation of a wear-resistant complex on the contact pads of a cutting tool, formed by ion nitriding followed by coating in a vacuum-arc discharge plasma, significantly affects the intensity and nature of tool wear.

Figures 5 and 6 show experimentally obtained profilograms of tool wear with a coating and with combined machining during longitudinal turning and face milling of 45 structural steel. its intensity.

For the operating conditions under consideration, there is a low efficiency of a tool with a coating without nitriding, both in milling and turning. This is due to the fact that the coating is destroyed very quickly and the friction conditions on the back surface are increasingly approaching those that are typical for an uncoated tool. And this means that the amount of released heat increases, the temperature near the rear surface increases, as a result of which irreversible softening processes begin in the tool material, which lead to catastrophic wear.

Studies of the nature of tool blunting with nitriding and coating allow us to conclude that the main contribution to reducing the wear intensity of a high-speed tool is made by the so-called "edge effect", which consists in the following.

Already in the first minutes of the tool operation, as can be seen from the profilograms of its working surfaces (Figures 5 and 6), the coating is destroyed to its entire thickness in areas near the cutting edge. However, further growth of wear centers along the length and depth is restrained by the edges of the contact areas, which retain the wear-resistant combination of the coating and the nitrided layer.

In addition, the surface nitrided layer, which has increased hardness combined with high heat resistance, is characterized by a higher resistance to microplastic deformations and contributes to the inhibition of softening processes at the rear surface.

Figure 5. Profilograms of worn sections of cutting inserts made of steel R6M5 when turning steel 45: a - R6M5 + (Ti, A1)N; b - Р6М5 + nitriding + (Ti, A1)N; processing modes: v = 82 m/min; S = 0.2 mm/rev; / = 1.5 mm (without coolant)

Figure 6. Profilograms of worn sections of cutting inserts made of R6M5 steel during face milling of steel 45: a - R6M5 + (Ti, Al)N; b - Р6М5 + nitriding + (Ti, Al)N; processing modes: v = 89 m/min; S= 0.15 mm/tooth; H = 45 mm;

Production experience shows that combined treatment, which provides for preliminary nitriding and subsequent coating, makes it possible to increase the tool life of the widest range of high-speed tools up to 5 and up to 3 times compared to tools without hardening and with a traditional coating, respectively.

Figure 7 shows the dependence of the change in wear over time h 3 \u003d f (T) of cutting inserts made of R6M5 steel that have passed different kinds surface hardening, during turning and face milling of steel 45. It can be seen that the resistance to catastrophic wear of the tool during turning increases by 2.6 times, and during milling - by 2.9 times compared with a tool with a coating, but without nitriding.

Figure 7. Dependence of wear along the flank surface of a tool made of steel R6M5 with different surface treatment options on cutting time: -- *-- R6M5 + (Ti, A1)N; --*-- Р6М5 + nitriding + (Ti-Al)N; a - turning steel 45 at v = 82 m / min; S = 0.2 mm/rev; /=1.5 mm; b - milling of steel 45: v = 89 m/min; 5= 0.15 mm/tooth; H = 45 mm; t = 1.5 mm

Ion-plasma hardening Vacuum ion-plasma methods for hardening the surfaces of parts include the following processes: generation (formation) of a corpuscular flow of matter; its activation, acceleration and focusing; ; condensation and penetration into the surface of parts (substrates). Generation: corpuscular flow of matter is possible by its evaporation (sublimation) and spraying. Evaporation: the transition of the condensed phase into vapor is carried out as a result of the supply of thermal energy to the evaporated substance. Solids usually melt when heated and then turn into a gaseous state. Some substances pass into the gaseous state bypassing the liquid phase. This process is called sublimation. .

Using the methods of vacuum ion-plasma technology, it is possible to perform: 1) modification of surface layers: ion-diffusion saturation; (ionic nitriding, carburizing, boriding, etc.); ion (plasma) etching (cleaning); ion implantation (implementation); glow discharge annealing; CTO in the environment of non-self-sustained discharge; 2) coating: glow discharge polymerization; ion deposition (triode sputtering system, diode sputtering system, using discharge in a hollow cathode); electric arc evaporation; ion-cluster method; cathode sputtering (dc, high frequency); chemical deposition in glow discharge plasma.

Advantages of vacuum ion-plasma hardening methods high adhesion of the coating to the substrate; uniformity of coating in thickness over a large area; variation of the coating composition in a wide range, within one technological cycle; obtaining high purity of the coating surface; environmental cleanliness of the production cycle.

Ion sputtering Ion sputters are divided into two groups: plasmonic sputters, in which the target is in a gas-discharge plasma created by a glow, arc, and high-frequency discharge. Sputtering occurs as a result of the bombardment of the target with ions extracted from the plasma; autonomous sources without focusing and with focusing of ion beams bombarding the target.

Principal spray system 1 - chamber; 2 - substrate holder; 3 - details (substrates); 4 - target; 5 - cathode; 6 - screen; 7 - supply of working gas; 8 - power supply; 9 - pumping out.

CTO in a glow discharge environment Glow discharge diffusion plants are used for nitriding, carburizing, siliconization and other types of CTO from the gas phase. The depth of the diffusion layer reaches several millimeters with uniform saturation of the entire surface of the product. The process is carried out at a reduced pressure of 10 -1 - 10 -3 Pa, which ensures the existence of a glow discharge. Advantages of using a glow discharge: high energy efficiency (consumption only for gas ionization and heating of the part); reducing the duration of the process, due to rapid heating to saturation temperature; increase in the activity of the gaseous medium and the surface layer; the possibility of obtaining coatings from refractory metals, alloys and chemical compounds. Disadvantages of the process: low pressure in the chamber (10 -1 Pa), low productivity, batch operation, impossibility of processing long products (for example, pipes), significant power consumption, high cost of installations.

Ion-diffusion saturation Advantages over conventional gas nitriding: cycle time reduction by 3-5 times; reduction of deformation of parts by 3-5 times; the possibility of carrying out controlled nitriding processes to obtain layers with a given composition and structure; the possibility of reducing the temperature of the nitriding process to 350 -400 0 С, which makes it possible to avoid softening of the core materials of the products; reducing the fragility of the layer and increasing its service characteristics; ease of protection of individual sections of parts from nitriding; elimination of the danger of furnace explosion; reduction in the specific consumption of electrical energy by 1.5-2 times and working gas by 30-50 times; improvement of working conditions for thermal workers. Disadvantages: the impossibility of accelerating the process by increasing the density of the ion flux, because as a result of overheating of the parts, the surface hardness decreases; intensification of the process of ion nitriding; applying a magnetic field to increase current density and reduce gas pressure; by creating the surface of the part of a given defectiveness (preliminary plastic deformation, heat treatment).

Ion carburizing unit EVT

Ionic cementation Ion cementation creates a high carbon concentration gradient in the boundary layer. The growth rate of the carburized layer of material is 0.4…0.6 mm/h, which is 3…5 times higher than for other carburizing methods. The duration of ion cementation to obtain a layer with a thickness of 1 ... 1.2 mm is reduced to 2 ... 3 hours. Due to the low consumption of gases, electricity and short processing times production costs decrease by 4 ... 5 times. The technological advantages of ion carburizing include high uniformity of carburization, the absence of external and internal oxidation, and a decrease in warping of parts. The volume of machining is reduced by 30%, the number of technological operations is reduced by 40%, the duration of the processing cycle is reduced by 50%.

Ion-plasma nitriding (IPA) IPA is a kind of chemical-thermal treatment of machine parts, tools, stamping and casting equipment, which provides diffusion saturation of the surface layer of steel (cast iron) with nitrogen or nitrogen and carbon in nitrogen-hydrogen plasma at a temperature of 450 - 600 ° C , as well as titanium or titanium alloys at a temperature of 800 - 950 ° C in nitrogen plasma. The essence of ion-plasma nitriding lies in the fact that in a nitrogen-containing gas medium discharged to 200–1000 Pa, between the cathode, on which the workpieces are located, and the anode, the role of which is played by the walls of the vacuum chamber, an abnormal glow discharge is excited, forming an active medium (ions, atoms, excited molecules). This ensures the formation of a nitrided layer on the surface of the product, consisting of an outer nitride zone with a diffusion zone located under it.

Microstructure of the nitrided layer of tool steel 4 X 5 MFS a b Microstructures of steels U 8 (a) and 20 X 13 (b) after ion-plasma nitriding

Installation UA-63 -950/3400 with variable geometry of the working chamber (height 1.7 or 3.4 m)

Application of the method of ion-plasma nitriding with this method, the following products are processed: nozzles for cars, automatic drive carrier plates, dies, punches, dies, molds (Daimler Chrysler); springs for the injection system (Opel); crankshafts (Audi); distribution (cam) shafts (Volkswagen); crankshafts for the compressor (Atlas, USA and Wabco, Germany); gears for BMW (Handl, Germany); bus gears (Voith); hardening of pressing tools in the production of aluminum products (Nughovens, Scandex, John Davis, etc.). There is a positive experience of the industrial use of this method by the CIS countries: Belarus - MZKT, MAZ, Bel. AZ; Russia - Auto. VAZ, Kam. AZ, MMPP Salyut, Ufa Engine Building Association (UMPO). The IPA method processes: gears (MZKT); gears and other parts (MAZ); gears of large (more than 800 mm) diameter (Bel. AZ); intake and exhaust valves (Avto. VAZ); crankshafts (Kam. AZ).

Metallization of products according to type 1 is carried out for decorative purposes, to increase hardness and wear resistance, to protect against corrosion. Due to the weak adhesion of the coating to the substrate, this type of metallization is not advisable for parts operating under high loads and temperatures. The technology of metallization according to types 1 and 2 a provides for the application of a layer of a substance on the surface of a cold or heated to relatively low temperatures product. These types of metallization include: electrolytic (electroplating); chemical; gas-flame processes for obtaining coatings (sputtering); coating by cladding (mechano-thermal); diffusion, immersion in molten metals. Metallization technology according to type 2 b provides for diffusion saturation of the surface of parts heated to high temperatures with metal elements, as a result of which an alloy is formed in the diffusion zone of the element (Diffusion metallization). In this case, the geometry and dimensions of the metallized part practically do not change.

Ion-plasma metallization Ion-plasma metallization has a number of significant advantages over other types of metallization. The high plasma temperature and neutral environment make it possible to obtain coatings with greater structural uniformity, lower oxidizability, higher cohesive and adhesive properties, wear resistance, etc. compared to these properties of other types of metallization. With this plating method, various refractory materials can be sputtered: tungsten, molybdenum, titanium, etc., hard alloys, as well as oxides of aluminum, chromium, magnesium, etc. Coating can be carried out by spraying both wire and powder. The actual metallization consists of three processes: melting of the solid metal of the wire or powder (during ion-plasma metallization), sputtering of the molten metal, and formation of a coating. The materials for spraying can be any refractory metals in the form of a wire or powder, but medium-carbon to alloyed wires of the Np-40, Np-ZOHGSA, Np-ZKh 13 types, etc. can also be used. In the conditions of car repair enterprises, an alloy of the type VZK (stellite) or sormite, which has high wear resistance and corrosion resistance.