We have developed and patented Avinit N method of plasma precision nitriding.
Avinit N plasma precision nitriding is a process of chemical heat treatment of machine parts and tools, surface layer diffusion saturation with nitrogen in the plasma of a non-self-containing gas discharge. Plasma-forming gas is nitrogen.
The process we offer is environmentally friendly, no hydrogen, ammonia or hydrogen-containing compounds are used in it. High-density plasma source is a gas plasma generator of Avinit® unit. Product temperature in the nitriding process for steels is 450-600°C, a similar process can be used for titanium and titanium alloys at temperatures of 600-800°C.С.
The essence of plasma nitriding:
Parts placed in a vacuum chamber are treated with high-density plasma in a discharged inert gas environment excited by a plasma generator.
As in other types of ion nitriding, the parts are the cathode and the walls of the vacuum chamber are the anode. Exposure to plasma results in heating of the parts. After heating to operating temperature, the plasma-forming gas in the chamber is replaced by nitrogen, resulting in formation of a nitrided layer on the product surface.
By varying the pressure, temperature and exposure time, as well as the discharge parameters, it is possible to obtain layers of a given structure and phase composition, ensuring strictly defined properties of the nitrided surfaces.
The Avinit N method is performed as follows:
In the chamber of the Avinit unit containing the gas-discharge plasma source (gas plasma generator), a preliminary vacuum of about 5-10-5 mm Hg is created. Then argon is injected through the gas plasma generator into the chamber up to pressure of 1-10-3 – 2·10-3 - 2-10-3 mm Hg. Negative bias potential is applied to the processed product, smoothly changing its value from 50 to 500-600 V, and ion cleaning of the surface is carried out. In this case the intensity of ion cleaning and temperature of the product heating is regulated by the discharge current of gas plasma generator.
The products are heated to a predetermined temperature in the range of 400 ... 500°C in argon gas-discharge plasma generated by the gas plasma generator.
Then a subsequent isothermal exposure in argon and nitrogen gas-discharge plasma also formed by a gas plasma generator is carried out.
At the third stage, nitriding proper is performed, when products are exposed at a predetermined temperature in a saturating nitrogen atmosphere, in which a high-density gas-discharge plasma, in which diffusion saturation is performed, contains nitrogen ions and is formed by a gas plasma generator.
Comparative characteristics of conventional nitriding processes and Avinit® N precision plasma nitriding are presented in Table 1 for industrially used steels 30Kh2H2VFA, 25Kh1MF, 20Kh3MVF and titanium alloy VT6.
При плазмовому азотуванні Avinit N при дифузійному насиченні азотом під впливом іонів газової суміші аргону і азоту, створюваних газовим плазмогенератором, досягається отримання дифузійного шару з рівномірною структурою зміцненого шару, підвищення твердості виробів зі сталей і сплавів при мінімальному коробленні і збереженні вихідних геометричних розмірів виробів за відсутності утворення крихкого шару нітридів заліза.
Nitriding with Avinit® N plasma treatment intensifies formation of nitrided layer by 3-5 times in comparison with conventional treatment by ion nitriding in the glow discharge. Product hardness is increased due to obtaining uniformly hardened nitrided layer without warping of products while maintaining the original geometric dimensions.
Product temperature during nitriding is 500-600°C for steels and 600-800°C for titanium and titanium alloys.
Experiments performed on plasma nitriding of alloyed steels, in particular, cemented, improved and nitrided steels and some heat-resistant structural steels have shown that plasma nitriding Avinit® N of such steels, which are not typical nitrated steels, provides the same, and often even higher properties of parts at lower cost of production than nitrided steels. For example, steels originally developed only for carburizing have also proven excellent after plasma nitriding with Avinit® N.
The surface hardness and nitriding depth achieved in this case are determined by the preceding heat treatment (duration and temperature of normalization, hardening temperature, temperature and duration of tempering), alloying element content and plasma nitriding conditions.
Advantages of Avinit N precision plasma nitriding.
The main advantages of the method are significant intensification of the nitriding process, obtaining a uniformly hardened nitrided layer, no brittle layer without warping of products while maintaining the original geometric dimensions of parts. After Avinit® precision plasma nitriding, the drawing dimensions are preserved and the brittle surface layer is eliminated, thus eliminating the need for finish grinding after nitriding and obtaining a nitriding operation "to size".
Use of the invention intensifies the process of formation of the nitrided layer by a factor of 3-5 as compared with conventional treatment by ion nitriding in the glow discharge and by a factor of 5-30 as compared with gas nitriding. The hardness and wear resistance of products are increased due to obtaining a uniformly hardened layer.
In comparison with widely used nitriding methods, the Avinit method of plasma precision nitriding has the following key advantages:
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- - no deformation of parts (warping) after treatment, stable quality of treatment with minimal variation of properties from part to part and from job to job;
- - No environmental contamination;
- - the process is environmentally friendly, no hydrogen, ammonia or hydrogen-containing compounds are used in it;
- - improvement of the production culture;
- - reduction of the cost of treatment.
The advantages of Avinit N plasma nitriding also manifest themselves in a significant reduction of key production costs. For example, in comparison with gas nitriding in furnaces, Avinit plasma nitriding provides:
- - reduction of processing time by 5 to 30 times, due to both reduced heating and cooling of the charge and reduced isothermal holding time;
- - Reduction in the consumption of working gases;
- - Reduction of power consumption;
- - Reducing deformation of parts, excluding finish grinding;
- - improvement of sanitary and hygienic conditions of production
- - full compliance of the technology with all modern requirements for environmental protection and ecological safety.
Processes of plasma precision nitriding eliminate the drawbacks of traditional industrial nitriding processes (conventional ion nitriding, liquid and gas nitriding), reduce their duration significantly, ensure stable high-quality microstructure of parts surface layers, eliminate their brittleness, increase the performance properties of parts, expand the range of processed materials.
For some precision complex-profile parts that do not allow warping at the level of 1...2 μm after nitriding and for which hard nitrided surfaces cannot be machined by high-precision grinding, Avinit N plasma nitriding "to size" is the only way to obtain a finished product.
Avinit N plasma precision nitriding is used in industrial production instead of traditional ion nitriding, liquid and gas nitriding.
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