Ionic nitriding of parts. Ion-plasma nitriding Type Protective pastes against ion-plasma nitriding

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 invariance 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 indicated, 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 in 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 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 on various operations mechanical processing shows that the presence of a nitrided layer under the coating, in which there is a brittle nitride zone (α- and β-phases), 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 processing in conditions of interrupted cutting optimal structure 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 steel R6M5, which have passed various types 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 to 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

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 nitriding is subjected to parts that have been hardened and ground, almost ready for release, but some qualities need to be improved.

The purpose of nitriding is associated with a change in the main performance qualities in the process of heating the part in an environment that is characterized by high concentration ammonia. Due to such an impact, the surface layer is saturated with nitrogen, and the part acquires the following performance 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 stability to mechanical impact.
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%. The best results are achieved when using 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:

The preliminary preparation of ammonia makes it possible to increase the proportion of solid solution diffusion, which reduces the proportion of reaction chemical processes when the active substance passes from environment into iron.
Provides for the use of special equipment that provides the most favorable conditions for 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 obtain critical details, which 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.

Nitriding, during which the surface layer of a steel product is saturated with nitrogen, has been used on an industrial scale relatively recently. Such a processing method, proposed for use by academician N.P. Chizhevsky, allows to improve many characteristics of products made of steel alloys.

The essence of technology

Nitriding of steel, when compared with such a popular method of processing this metal as carburizing, has a number of significant advantages. That's why this technology began to be used as the main way to improve the quality characteristics of steel.

During nitriding, the steel product is not subjected to significant thermal effects, while the hardness of its surface layer increases significantly. It is important that the dimensions of the nitrided parts do not change. This makes it possible to use this processing method for steel products that have already been hardened with high tempering and ground to the required geometric parameters. After nitriding, or nitriding as the process is often referred to, the steel can be immediately subjected to polishing or other finishing methods.

Nitriding of steel consists in the fact that the metal is subjected to heating in an environment characterized by a high content of ammonia. As a result of such treatment, the following changes occur with the surface layer of the metal saturated with nitrogen.

Due to the fact that the hardness of the surface layer of steel increases, the wear resistance of the part improves.
The fatigue strength of the product increases.
The surface of the product becomes resistant to corrosion. Such stability is maintained when steel comes into contact with water, moist air and steam-air medium.

The performance of nitriding makes it possible to obtain more stable indicators of steel hardness than when carburizing. Thus, the surface layer of a product that has been subjected to nitriding retains its hardness even when heated to a temperature of 550–600°C, while after cementation, the hardness of the surface layer may begin to decrease even when the product is heated above 225°C. The strength characteristics of the surface layer of steel after nitriding are 1.5–2 times higher than after hardening or carburizing.

How does the nitriding process proceed?

Metal parts are placed in a hermetically sealed muffle, which is then installed in a nitriding furnace. In the furnace, the muffle with the part is heated to a temperature, which is usually in the range of 500–600°C, and then kept for some time at this temperature regime.

In order to form the working medium inside the muffle necessary for the nitriding to proceed, ammonia is supplied to it under pressure. When heated, ammonia begins to decompose into its constituent elements, this process is described by the following chemical formula:

2NH 3 → 6H + 2N.

Atomic nitrogen released during such a reaction begins to diffuse into the metal from which the workpiece is made, which leads to the formation of nitrides on its surface, which are characterized by high hardness. To fix the result and prevent the surface of the part from oxidizing, the muffle, together with the product and the ammonia that continues to remain in it, is slowly cooled together with the nitriding furnace.

The nitride layer formed on the metal surface during nitriding can have a thickness in the range of 0.3–0.6 mm. This is quite enough to give the product the required strength characteristics. Steel processed using this technology can not be subjected to any additional processing methods.

The processes occurring in the surface layer of a steel product during its nitriding are quite complex, but have already been well studied by specialists in the metallurgical industry. As a result of such processes, the following phases are formed in the structure of the treated metal:

solid solution Fe 3 N, characterized by a nitrogen content in the range of 8–11.2%;
a solid solution of Fe 4 N, which contains 5.7–6.1% nitrogen;
nitrogen solution formed in α-iron.

An additional α-phase in the metal structure is formed when the nitriding temperature begins to exceed 591°. At the moment when the degree of saturation of a given phase with nitrogen reaches its maximum, a new phase is formed in the metal structure. Eutectoid decomposition in the metal structure occurs when the degree of its saturation with nitrogen reaches a level of 2.35%.

Valves of high-tech internal combustion engines must undergo a nitriding process

Factors affecting nitrogenation

The main factors that affect nitriding are:

the temperature at which such a technological operation is performed;
gas pressure supplied to the muffle;
the duration of exposure of the part in the furnace.

The efficiency of such a process is also affected by the degree of ammonia dissociation, which, as a rule, is in the range of 15–45%. With an increase in the nitriding temperature, the hardness of the formed layer decreases, but the process of nitrogen diffusion into the metal structure accelerates. The decrease in the hardness of the surface layer of the metal during its nitriding occurs due to the coagulation of the nitrides of the alloying elements included in its composition.

To speed up the nitriding process and increase its efficiency, a two-stage scheme of its implementation is used. The first stage of nitriding when using such a scheme is performed at a temperature not exceeding 525 °. This makes it possible to impart high hardness to the surface layer of the steel product. To perform the second stage of the procedure, the part is heated to a temperature of 600–620°, while the depth of the nitrided layer reaches the required values, and the process itself is almost doubled. The hardness of the surface layer of a steel product processed using this technology is not lower than the similar parameter of products processed using a single-stage method.

Types of nitrided steels

Both carbonaceous and those characterized by a carbon content in the range of 0.3–0.5% can be processed using nitriding technology. The maximum effect when using such a technological operation can be achieved if steels are subjected to it, in chemical composition which include alloying elements that form solid and heat-resistant nitrides. Such elements, in particular, include molybdenum, aluminum, chromium and other metals with similar characteristics. Steels containing molybdenum are not subject to such a negative phenomenon as temper brittleness, which occurs when a steel product slowly cools. After nitriding steel of various grades acquire the following hardness:

Alloying elements in the chemical composition of the steel increase the hardness of the nitrided layer, but at the same time reduce its thickness. Such chemical elements as tungsten, molybdenum, chromium and nickel have the most active influence on the thickness of the nitrided layer.

Depending on the scope of the product that is subjected to the nitriding procedure, as well as on the conditions of its operation, it is recommended to use certain steel grades for such a technological operation. So, in accordance with the technological problem that needs to be solved, experts advise using products from the following steel grades for nitriding.

38X2MYUA

This is a steel that, after nitriding, has a high hardness of the outer surface. Aluminum contained in the chemical composition of such steel reduces the deformation resistance of the product, but at the same time contributes to an increase in the hardness and wear resistance of its outer surface. The exclusion of aluminum from the chemical composition of steel makes it possible to create products of a more complex configuration from it.

40X, 40HFA

These alloyed steels are used for the manufacture of parts used in the machine tool industry.

30H3M, 38HGM, 38HNMFA, 38HN3MA

These steels are used for the production of products that are subjected to frequent cyclic bending loads during their operation.

30X3MF1

Products are made from this steel alloy, the accuracy of geometrical parameters of which is subject to high requirements. To give higher hardness to parts made of this steel (these are mainly parts of fuel equipment), silicon can be added to its chemical composition.

Technological scheme of nitriding

To perform conventional gas nitriding, innovative plasma nitriding or ion nitriding, the workpiece is subjected to a series of process steps.

Preparatory heat treatment

Such processing consists in hardening the product and its high tempering. Hardening as part of this procedure is carried out at a temperature of about 940 °, while cooling the workpiece is carried out in oil or water. The subsequent tempering after quenching, which takes place at a temperature of 600–700 °, makes it possible to endow the metal being processed with a hardness at which it can be easily cut.

Mechanical restoration

This operation ends with its grinding, which allows to bring the geometric parameters of the part to the required values.

Protection of parts of the product that do not require nitriding

Such protection is carried out by applying a thin layer (not more than 0.015 mm) of tin or liquid glass. For this, electrolysis technology is used. The film of these materials, which is formed on the surface of the product, does not allow nitrogen to penetrate into its internal structure.

Performing the nitriding itself

The prepared product is subjected to processing in a gaseous environment.

Finishing

This stage is necessary in order to bring the geometric and mechanical characteristics products to the required values.

The degree of change in the geometric parameters of the part during nitriding, as mentioned above, is very small, and it depends on factors such as the thickness of the surface layer that is saturated with nitrogen; temperature regime of the procedure. Guaranteed practically complete absence deformation of the workpiece allows a more advanced technology - ion nitriding. When performing ion-plasma nitriding, steel products are subjected to less thermal impact, due to which their deformation is minimized.

Unlike the innovative ion-plasma nitriding, traditional nitriding can be performed at temperatures up to 700°C. For this, a replaceable muffle or a muffle built into the heating furnace can be used. The use of a replaceable muffle, in which the workpieces are loaded in advance, before being installed in the furnace, can significantly speed up the nitriding process, but is not always an economically viable option (especially in cases where large-sized products are processed).

Working environment types

Various types of media can be used to perform nitriding. The most common of these is a gas medium consisting of 50% ammonia and 50% propane or ammonia and endogas, taken in the same proportions. The nitriding process in such an environment is carried out at a temperature of 570 °. In this case, the product is exposed to the gas environment for 3 hours. The nitrided layer created by using such a working medium has a small thickness, but high strength and wear resistance.

Recently, the method of ion-plasma nitriding, which is performed in a nitrogen-containing discharged medium, has been widely used.

Ion-plasma nitriding - a look "from the inside"

A distinctive feature of ion-plasma nitriding, which is also called glow discharge treatment, is that the workpiece and the muffle are connected to an electric current source, while the workpiece acts as a negatively charged electrode, and the muffle acts as a positively charged one. As a result, an ion flow is formed between the part and the muffle - a kind of plasma consisting of N 2 or NH 3, due to which both the heating of the treated surface and its saturation occur necessary quantity nitrogen.

In addition to traditional and ion-plasma nitriding, the process of saturation of the steel surface with nitrogen can be performed in a liquid medium. As a working medium, which has a heating temperature of about 570 °, in such cases, a melt of cyanide salts is used. The time of nitriding carried out in a liquid working medium can be from 30 to 180 minutes.

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, when heated, they melt, and then go 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 methods ion-plasma hardening 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, siliciding 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 performance characteristics; ease of protection of individual sections of parts from nitriding; elimination of the danger of furnace explosion; reduction in unit costs electrical energy 1.5-2 times and working gas 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 is 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, bearing plates of automatic drive, 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 industrial use this method 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. Using this method of metallization, it is possible to spray various refractory materials: 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 such as Np-40, Np-ZOHGSA, Np-ZKh 13, 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.

Ion-plasma nitriding (IPA) is a method of chemical-thermal treatment of steel and cast iron products with great technological capabilities, which makes it possible to obtain diffusion layers of the desired composition by using different gaseous media, i.e. the diffusion saturation process is controllable and can be optimized depending on the specific requirements for layer depth and surface hardness. plasma nitriding microhardness alloyed

The temperature range of ion nitriding is wider than gas nitriding and is within 400-600 0 С. their operational properties are significantly increased while maintaining the hardness of the core at the level of 55-60 HRC.

Parts and tools of almost all industries are subjected to hardening treatment by the IPA method (Fig. 1).

Rice. one.

As a result of IPA, the following characteristics of products can be improved: wear resistance, fatigue endurance, extreme pressure properties, heat resistance and corrosion resistance.

In comparison with the widely used methods of hardening chemical-thermal treatment of steel parts, such as carburizing, carbonitriding, cyanidation and gas nitriding in furnaces, the IPA method has the following main advantages:

higher surface hardness of nitrided parts;
no deformation of parts after processing and high surface finish;
increase in endurance limit and increase in wear resistance of machined parts;
lower processing temperature, due to which structural transformations do not occur in the steel;
Possibility of processing deaf and through holes;
· maintaining the hardness of the nitrided layer after heating to 600-650 C;
the possibility of obtaining layers of a given composition;
the possibility of processing products of unlimited sizes and shapes;
no pollution of the environment;
Improving the culture of production;
Reducing the cost of processing several times.

The advantages of IPA are also manifested in a significant reduction in the main production costs.

So, for example, in comparison with gas nitriding in furnaces, IPA provides:

· reduction of processing time by 2-5 times, both by reducing the heating and cooling time of the charge, and by reducing the isothermal holding time;
· reduction of brittleness of the hardened layer;
· Reducing the consumption of working gases by 20-100 times;
· reduction of power consumption by 1.5-3 times;
exclusion of the depassivation operation;
reduction of deformation so as to exclude finishing grinding;
· simplicity and reliability of screen protection against nitriding of unhardened surfaces;
· improvement of sanitary and hygienic conditions of production;
full compliance with the technology for all modern requirements for environmental protection.

Compared to hardening IPA processing allows:

Avoid deformities
· to increase the service life of the nitrided surface by 2-5 times.

The use of IPA instead of carburizing, nitrocarburizing, gas or liquid nitriding, volumetric or high-frequency hardening allows saving the main equipment and production areas, reducing machine and transportation costs, reducing the consumption of electricity and active gaseous media.

The principle of operation of the IPA is that in a discharged (p = 200-1000 Pa) nitrogen-containing gaseous medium between the cathode - parts - and the anode - the walls of the vacuum chamber - an abnormal glow discharge is excited, forming an active medium (ions, atoms, excited molecules), providing the formation of a nitrided layer, consisting of an external - nitride zone and a diffusion zone located under it.

Technological factors affecting the efficiency of ion nitriding are the process temperature, duration of saturation, pressure, composition and consumption of the working gas mixture.

Process temperature, the area of the charge involved in heat exchange and the efficiency of heat exchange with the wall (the number of screens) determine the power required to maintain the discharge and provide the desired temperature of the products. The choice of temperature depends on the degree of alloying of the nitrided steel with nitride-forming elements: the higher the degree of alloying, the higher the temperature.

The processing temperature should be at least 10-20 0 С lower than the tempering temperature.

Process duration and temperature saturations determine the depth of the layer, the distribution of hardness over depth, and the thickness of the nitride zone.

The composition of the saturating medium depends on the degree of alloying of the treated steel and the requirements for hardness and depth of the nitrided layer.

Process pressure should be such as to ensure a tight "fit" by the discharge of the surface of the products and obtain a uniform nitrided layer. However, it should be borne in mind that the discharge at all stages of the process must be anomalous, i.e., the surface of all parts in the charge must be completely covered with luminescence, and the discharge current density must be greater than the normal density for a given pressure, taking into account the heating effect gas in the cathode region of the discharge.

With the advent of new generation IPA units, which use composition-controlled mixtures of hydrogen, nitrogen and argon as a working medium, as well as “pulsating” rather than direct current plasma, the manufacturability of the ion nitriding process has increased significantly.

The use of combined heating (“hot” walls of the chamber) or enhanced thermal protection (triple heat shield), along with the ability to independently adjust the gas composition and pressure in the chamber, make it possible to avoid overheating of thin cutting edges during the heating of the charge during processing of the cutting tool, to precisely control the saturation time and , respectively, and the depth of the layer, because products can be heated in a nitrogen-free environment, for example, in a mixture of Ar+H 2 .

Efficient thermal insulation in the working chamber (triple heat shield) allows the processing of products with low specific energy consumption, which allows minimizing temperature differences within the load during processing. This is evidenced by the distribution of microhardness over the depth of the nitrided layer for samples located in different places of the charge (Fig. 2).

Rice. 2.

a, c - gear weighing 10.1 kg, 51 pieces, st - 40X, module 4.5, exposure 16 hours, T = 530 0 C;

b, d - gear weighing 45 kg, 11 pcs., st - 38KhN3MFA, module 3.25 (outer crown) and 7 mm (inner crown), exposure 16 hours, T = 555 0 C.

Ion nitriding is an effective method of hardening treatment of parts made of alloy structural steels: gears, gear rims, gear shafts, shafts, spur, bevel and cylindrical gears, couplings, gear shafts of complex geometric configuration, etc.

Carburizing, nitrocarburizing and high-frequency hardening justify themselves in the manufacture of heavily loaded parts (gear wheels, axles, shafts, etc.) of low and medium accuracy that do not require subsequent grinding.

These types of heat treatment are not economically feasible in the manufacture of medium- and low-loaded high-precision parts, because with this treatment, significant warping is observed and subsequent grinding is required. Accordingly, when grinding, it is necessary to remove a significant thickness of the hardened layer.

IPA can significantly reduce warping and deformation of parts while maintaining surface roughness within Ra = 0.63 ... 1.2 µm, which allows in the vast majority of cases to use IPA as a finishing treatment.

As applied to the machine tool industry, ion nitriding of gears significantly reduces the noise characteristics of machine tools, thereby increasing their competitiveness in the market.

IPA is most effective when machining large-scale similar parts: gears, shafts, axles, toothed shafts, shaft-toothed gears, etc. Plasma nitrided gears have better dimensional stability compared to carburized gears and can be used without additional processing. At the same time, the bearing capacity of the side surface and the strength of the tooth base, achieved using plasma nitriding, correspond to case-hardened gears (Table 1).

Table 1. Characteristics of fatigue resistance of steels depending on the methods of hardening gears

During hardening treatment by ion nitriding of parts made of carburized, low- and medium-alloy steels (18KhGT, 20KhNZA, 20KhGNM, 25KhGT, 40Kh, 40KhN, 40KhFA, etc.), it is necessary to improve forgings at the beginning - volumetric hardening and tempering to a hardness of 241-285 HB (for some steels - 269-302 HB), then machining and, finally, ion nitriding. In order to ensure minimum deformation of products before stress-relieving nitriding, it is recommended to carry out annealing in a protective gas atmosphere, and the annealing temperature should be higher than the nitriding temperature. Annealing should be carried out before precise machining.

The depth of the nitrided layer formed on these products, made of steels 40Kh, 18KhGT, 25KhGT, 20Kh2N4A, etc., is 0.3-0.5 mm with a hardness of 500-800 HV, depending on the steel grade (Fig. 3).

For gears operating under conditions of heavier loads, the nitrided layer should be at the level of 0.6-0.8 mm with a thin nitride zone or without it at all.

Rice. 3.

The optimization of the properties of the hardened layer is determined by the combination of the characteristics of the base material (hardness of the core) and the parameters of the nitrided layer. The nature of the load determines the depth of the diffusion layer, the type and thickness of the nitride layer:

wear - "- or - layer;
· dynamic load - limited thickness of the nitride layer or no nitride layer at all;
· corrosion - - a layer.

Independent control of the flow rate of each of the components of the gas mixture, the pressure in the working chamber and the variation in the temperature of the process make it possible to form layers of different depths and hardness (Fig. 4), thereby ensuring a stable quality of processing with a minimum spread of properties from part to part and from charge to charge ( Fig. 5).

Rice. 4.

1, 3, 5 -one-step process;
2,4 - two-stage process by N content 2 in the working mixture
1,2 - T=530 0 C, t=16 hours; 3 - T=560 0 C, t=16 hours;
4 - T=555 0 C, t=15 hours, 5 - T = 460 0 C, t = 16 hours

Rice. five.

Ion nitriding is widely known as one of the effective methods increase the wear resistance of cutting tools made of high speed steels grades R6M5, R18, R6M5K5, R12F4K5, etc.

Nitriding increases tool wear resistance and heat resistance. The nitrided surface of the tool, which has a reduced coefficient of friction and improved anti-friction properties, provides easier chip removal, and also prevents chips from sticking to the cutting edges and the formation of wear holes, which makes it possible to increase the feed and cutting speed.

The optimal structure of nitrided high-speed steel is high-nitrogen martensite, which does not contain excess nitrides. This structure is provided by saturation of the tool surface with nitrogen at a temperature of 480-520 0 C during short-term nitriding (up to 1 hour). In this case, a hardened layer with a depth of 20–40 μm is formed with a surface microhardness of 1000–1200 HV0.5 with a core hardness of 800–900 HV (Fig. 6), and the tool life after ion nitriding increases 2–8 times depending on its type and type of material being processed.

Rice. 6.

The main advantage of ion nitriding of the tool is the possibility of obtaining only a diffusion hardened layer, or a layer with monophase Fe 4 N nitride ("-phase") on the surface, in contrast to classical gas nitriding in ammonia, where the nitride layer consists of two phases - "+", which is a source of internal stresses at the phase boundary and causes brittleness and peeling of the hardened layer during operation.

Ion nitriding is also one of the main methods for increasing durability. stamping tools and injection molding equipment from steels 5KhNM, 4Kh5MFS, 3Kh2V8, 4Kh5V2FS, 4Kh4VMFS, 38Kh2MYUA, Kh12, Kh12M, Kh12F1.

As a result of ion nitriding, the following characteristics of products can be improved:

· Forging dies for hot stamping and molds for casting metals and alloys - wear resistance is increased, metal sticking is reduced.
· Aluminum Die Casting Molds - The nitrided layer prevents metal from sticking in the liquid jet area, and the mold filling process is less turbulent, which increases the life of the molds, and the casting is of higher quality.

Significantly improves ion nitriding and tool performance for cold (T< 250 0 С) обработки - вытяжка, гибка, штамповка, прессование, резка, чеканка и прошивка.

The main requirements that ensure the high performance of such a tool - high compressive strength, wear resistance and resistance to cold shock loading - are achieved as a result of hardening treatment by ion nitriding.

If high-chromium steel (12% chromium) is used for the tool, then the nitrided layer should be only diffusion, if low-alloy steels, then in addition to the diffusion layer there should be a z-layer - hard and ductile.

A feature of ion nitriding of high-chromium steels is that by choosing the process temperature, it is possible to maintain the hardness of the core of the product in a wide range, which is set by preliminary heat treatment (Table 2).

To obtain a wear-resistant surface layer while maintaining a ductile die core, it is first necessary to carry out quenching with tempering for secondary hardness, dimensional processing, and then ion nitriding.

To avoid or minimize deformations that occur during ion nitriding of a stamping tool, it is recommended to carry out annealing in an inert gas atmosphere at a temperature of at least 20 ° C below the tempering temperature before final machining.

If necessary, apply polishing of nitrided working surfaces.

Table 2. Characteristics of alloyed steels after ion-plasma nitriding.

steel grade	Core hardness, HRC	Process temperature	Layer characteristics	Type of recommended connection layer
	Depth, mm	Pov. TV-st, HV 1	Connection layer thickness, µm
Steels for hot working




Steels for cold working

By varying the composition of the saturating medium, the temperature of the process and its duration, it is possible to form layers of different depths and hardness (Fig. 7.8).

punch weighing 237 kg
mold weighing 1060 kg.

Rice. 7. Examples of die tooling processing (a, b) and distribution of microhardness over the depth of the nitrided layer (c, d).

Thus, as world experience shows, the use of ion nitriding technology for hardening processing of products made of structural steels, as well as cutting and stamping tools, this technology is effective and relatively easy to implement, especially with the use of pulsating current plasma.

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