Procedure for creation of macro non-uniform structure of material at nitriding

FIELD: metallurgy.

SUBSTANCE: procedure for treatment of parts out of titanium alloys consists in cathode sputtering and nitriding. Before and after nitriding parts are annealed in vacuum. For nitriding there is supplied mixture of gases consisting of 10 wt % of nitrogen and 90 wt % of argon. Further, parts are vacuum heated in non-uniform plasma of higher density which is created between a part and a screen due to effect of a hollow cathode. Thus there is facilitated formation of regular macro non-uniform structure. Structure of cells of the screen is honeycomb-like. Parts are annealed before and after nitriding at temperature 800°C during 2 hours, while nitriding is carried out at temperature below α→β of transition of titanium alloy.

EFFECT: increased contact durability and wear resistance of hardened layer due to creation of regular macro non-uniform structure of material, expanded functionality of described procedure.

2 cl, 4 dwg, 2 ex

 

The invention relates to the field of thermal, chemical and thermal processing and can be used in engineering and other industries for surface hardening materials.

The known method (Patent RF № 2058421, CL SS 8/36, 20.04.96) nitriding parts of the structural alloy steels, including high-temperature ion nitriding, quenching from the temperature of complete dissolution of nitride phases, vacation, finish machining and low-temperature ion nitriding at a depth of not less depth diasteranes layer.

The disadvantage of analog is

- the complexity of the equipment and technology, and the need to design special equipment,

- there is no possibility of creating macronational structure.

The known method (Patent RF № 2127330, CL SS 8/26. 10.03.99) heat treatment for the formation of high-strength austenitic surface layer in stainless steels, including nitriding in containing nitrogen gas atmosphere at 1000-1200°C and subsequent cooling at a rate that permits to avoid selecting nitride.

The disadvantage of analog is

- the complexity of the equipment and technology, and the need to design special equipment,

- there is no possibility of creating macronational structure.

Known methods for the (Patent RF № 2219271, CL SS 1/10, SS 5/00, C21D 1/28, 2003.12.20) hardening of the alloy based on iron containing free and bound carbon, which consists in smelting the alloy, the pressure treatment and receiving the products with the subsequent transfer of free carbon in an amount of 0.1-100% associated with iron status, by heating at 723-1100°C and holding at this temperature for 0.1 to 100 hours

The disadvantage of analog is

- the complexity of the equipment and technology, and the need to design special equipment,

- there is no possibility of creating macronational structure.

The closest in technical essence and the achieved effect to the claimed is a method (Patent RF № 2276201, CL SS 8/36, C21D 9/30, 09.11.2004) processing of steel products, including nitriding in a glow discharge, for which conduct cathode sputtering, vacuum heating products in the plasma of nitrogen increased density generated between the part and the screen through the creation of hollow cathode effect.

The disadvantage of the prototype is

most likely decarburization of the surface, which can lead to a sharp increase in the fragility of the nitrided layer and peeling, due to the lack of carbon-containing gases in the saturating medium,

- there is no possibility of creating macronational structure.

The task, which is opravleno the present invention, is to increase the contact durability and wear resistance of the hardened layer by obtaining regular macronational material structure, as well as expanding the functionality of this method, due to the preliminary annealing, nitriding in an inhomogeneous plasma glow discharge.

The problem is solved through the use of the method of machining of titanium alloys, including cathodic sputtering and nitriding, according to the invention before and after nitriding conduct annealing in vacuum, the nitriding is carried out by feeding a mixture of gases, consisting of 10 wt.% nitrogen and 90 wt.% argon, and vacuum heating in an inhomogeneous plasma of high density is formed between the part and the screen by creating the effect of a hollow cathode with ensuring a regular macronational structure when the screen do with the structure of the cells in the honeycomb.

In addition, according to the invention, the annealing before and after nitriding is carried out at a temperature of 800°C. for 2 hours, and the nitriding is at a temperature below the α→β transition titanium alloy.

Annealing in vacuum is carried out before nitriding the purpose of stress relieving and preventing wrinkling.

Differentiated treatment that combines the total (bulk) and local (local) impacts on material, enables you to get the regulator is ing macronational structure on the surface, and in the volume of the alloys. Differentiated structure is created monomateriale by getting in heterogeneous it structures. Between areas with different structures, there is a transition area with a microheterogeneous structure in which the structure gradually changes from one form to another, which ensures good compatibility between areas with different properties. Thereby possible to obtain sections with alternating strength and plastic properties both on the surface and in the bulk of the material.

For local thermal and chemical processing to create macronational structure of the material used inhomogeneous plasma glow discharge with hollow cathode.

The inhomogeneity of the plasma is provided by the hollow cathode effect.

The hollow cathode effect is manifested by the significant increase in current density, increasing the degree of ionization of an inhomogeneous plasma, while reducing stress burning discharge, and the surface of the part directly becomes the surface of the hollow cathode.

The screen has the structure of a cell, made in the form of honeycomb, which is the most optimal from the point of view of distribution of energy components on the surface of the hollow cathode, thereby providing optimal macroinhomogeneity on the surface, that is in the product volume that, in turn, contributes to the different use of such materials.

The invention is illustrated by drawings.

Figure 1 shows the types of differentiated patterns: 1 - bar, 2 - point, 3 - mesh, 4 - layered. Figure 2 shows the distribution of hardness of the surface hardened layer in a glow discharge with the EPA, where a, b - parameters of the screen (the cell size), 5 - screen, 6 - processed surface, 7 - zone normal glow discharge, 8 - zone of high particle concentration (EPC). Figure 3 shows the model compound of the screen, where a is the cell size, b is the distance between cells, a=b. Figure 4 depicts the implementation of the method of the intensified effect of the hollow cathode to obtain a heterogeneous structure. The circuit contains a power source 9, the anode 10, the screen 5 is mounted at a certain distance from the cathode-workpiece 11.

A specific example of implementation of the method.

Example 1.

The method is as follows: in a vacuum chamber set the workpiece and the screen is made with the structure in the form of honeycombs, connecting to the negative electrode, seal chamber and pump out the air to a pressure of 100 PA. Then conduct a preliminary annealing in vacuum. Then, after evacuation of the air chamber purge the working gas 5-15 minutes at a pressure of 1000-1330 PA, then pumped the camera is about pressure 50 PA, served on the electrode voltage and excite glow discharge. When the voltage 1000-1400 In at this stage, carry out cathodic sputtering. After 5-15 minutes processing mode, cathode sputtering voltage is reduced to the worker, and the pressure is increased to 100 PA. Then the camera create a working pressure of 100 PA required for ignition of the glow discharge. The camera serves a mixture of gases - nitrogen-argon, in the following ratio, wt.%:

N2- 10,

Ar - 90.

Using the hollow cathode effect is heating of the parts, thus there is a nitriding in an inhomogeneous plasma of high density is formed between the part and the screen for creating macronational structure of the material. All processes take place in one process cycle, one camera and one atmosphere. After processing, the product is cooled together with the vacuum chamber under vacuum. Creating macronational structure increases the contact durability and wear resistance of the hardened layer.

Example 2, in particular for titanium alloys.

The purpose of stress relieving and preventing wrinkling of the material, prior to nitriding the surface of the conducting short-term annealing in vacuum at 800°C for 2 hours.

To reduce the fragility of the diffusion layer and increase by 10...15% characteristics of the plasticity of the alloys after nitriding recommend an additional annealing of parts in vacuum at vacuum 4·10 -2PA for 2 hours, at a temperature of 800°C.

Directly nitriding is carried out at a temperature below the α→β transition, during which the alloy is formed of a two-phase (α+β)-structure, and the nitrogen has a significant effect on phase equilibria, even a very low concentration of nitrogen increases the transition temperature in the β-region.

The presence of different nitrogen concentration at the same temperature causes the equilibrium between the α - and β-phases is achieved when different proportions, the number of equilibrium α phase increases, which is more favorable, because the nitrogen is dissolved mainly in the α-phase.

Surface hardening occurs due to the formation of titanium nitride TiN, the amount of which increases generally with increasing duration of nitriding.

Creating macronational patterns in products leads to increased contact durability and wear resistance of the hardened layer.

1. The method of machining of titanium alloys, including cathodic sputtering and nitriding, characterized in that before and after nitriding conduct annealing in vacuum, the nitriding is carried out by feeding a mixture of gases, consisting of 10 wt.% nitrogen and 90 wt.% argon, and vacuum heating in an inhomogeneous plasma high-density fo Miramas between the part and the screen by creating the effect of a hollow cathode with ensuring a regular macronational patterns, when this screen do with the structure of the cells in the honeycomb.

2. The method according to claim 1, characterized in that the annealing before and after nitriding is carried out at a temperature of 800°C for 2 h, and the nitriding is at a temperature below the α→β transition titanium alloy.



 

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