RU2712661C1 - Method for formation of tribological coating - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: invention can be used in machine building and micromechanics to reduce friction and wear in friction bearings. First, working surface of articles 1 is prepared by polishing, degreasing in an ultrasonic bath, treatment with a petrol-alcohol mixture and thermal treatment in a drying cabinet. Prepared articles 1 are placed in vacuum chamber 2, insulated from its housing and connected to pulse negative voltage source (bias voltage). Simultaneously with evacuation of vacuum chamber 2 it is heated by heaters 5 for intensification of degassing process. After supply of plasma-forming gas - argon into vacuum chamber 2, metal surface of articles 1 is subjected to ion etching, for this purpose magnetron 4 is switched on. Then nitrogen is added and simultaneous nitriding at heating of articles 1 surface is performed up to 200÷500 °C. Then, surface of articles 1 is coated with transition layer of at least one layer of metal, metal carbide or metal nitride at varying negative bias voltage and flow of reaction gas, the flow rate of which is increased simultaneously with reduction of bias voltage. After formation of transition layer, magnetron 4 is switched off, negative voltage is supplied to articles 1 and magnetron 3 is applied to apply main coating layer by means of high-power pulse magnetron sputtering after heating of target from Al_0.75Mg_0.75B₁₄.

EFFECT: higher quality and service life of coating due to increased allowable contact loads and reduced coefficient of friction.

1 cl, 2 dwg

Description

The invention relates to tribology in mechanical engineering, micromechanics and can be used to reduce friction and wear in loaded friction pairs, such as, for example, plain bearings.

A tribological coating is known (patent US 80390966 IPC B05D3 / 00, published October 18, 2011), in which it is proposed to conduct ion cleaning on the surface of a metal part, then spray the intermediate layer of chromium or chromium nitride, an Al layer of _0.75 Mg _0.75 B ₁₄ (hereinafter referred to as BAM), to form a transition region and apply a second layer based on carbon, the task of which is to smooth out surface irregularities and provide a low surface roughness R _a .

The disadvantages of this technical solution are the deformation of the surface region of a softer metal base with significant mechanical stress on the friction pair, which causes cracking and delamination of the coating, as well as high surface roughness R _a due to the small thickness of the leveling layer.

The closest in technical essence to the proposed invention is the invention (patent No. US 6331332 B1, IPC C 14/06, publ. 12/18/2001), which proposes a method of forming a tribological coating of diamond-like carbon (Diamond-like carbon - DLC) by the cathode arc method spraying. It includes ion etching of the surface of the product, applying a transition coating layer of at least one layer of metal, metal carbide or metal nitride, the formation of the main coating layer (DLC) by electrochemical decomposition of carbon-containing gas (acetylene) by means of an electric arc discharge with separation in a vacuum chamber .

The disadvantages of this method are the deformation of the surface region of a softer metal base with significant mechanical stress on a couple of friction and the presence of coating defects that increase the surface roughness of the product and worsen the performance properties of the coating.

The technical task of the invention is to reduce the deformation of the surface region of the metal base of the product and reduce the surface roughness of the coating.

The technical result consists in improving the quality and service life of the coating by increasing the allowable contact loads and reducing the coefficient of friction.

This is achieved by the fact that in the known method of applying a tribological coating, including ion etching of the surface of the product, applying a transition coating layer of at least one layer of metal, metal carbide or metal nitride, applying the main coating layer (DLC) by electrochemical decomposition of carbon-containing gas (acetylene) by means of an electric arc discharge with separation in a vacuum chamber, an operation of ion-plasma nitriding combined with etching of a metal erhnosti product applied transition layer of at least one layer of metal, metal carbide or metal nitride with time-varying offset voltage and the flow of the reaction gas, the primary coating layer is applied to high-power pulsed magnetron sputtering Al _0,75 Mg _0,75 B ₁₄ material.

The invention is illustrated by drawings, where figure 1 shows a device for implementing the method, figure 2 shows the structure of the formed coating.

A device for implementing the method comprises articles 1, a vacuum chamber 2, a magnetron 3 with a target of Al _0.75 Mg _0.75 B ₁₄ , a magnetron 4 with a metal target, and heaters 5.

The structure of the formed coating contains the main material of the product 6, a modified (nitrided) layer 7, a transition coating layer of at least one metal layer, metal carbide or metal nitride 8 and the main layer 9 of Al _0.75 Mg _0.75 B ₁₄ .

The method of applying tribological wear-resistant coating is as follows.

The surface preparation of the products 1 is as follows: the working surface of the products 1 is polished, degreased in an ultrasonic bath, treated with a gasoline-alcohol mixture, and subjected to heat treatment in an oven. Thus prepared products 1 are placed in a vacuum chamber 2. Products 1 are isolated from the housing of the vacuum chamber 2 and connected to a source of pulse negative voltage (bias voltage).

Pumping of the vacuum chamber 2 occurs simultaneously with its heating by the heaters 5 to intensify the degassing process of the chamber 2 and products 1. Then, inert gas argon is introduced into the vacuum chamber 2.

Combined ion etching and ion-plasma nitriding (surface modification) of the cleaned surface of the products 1 is carried out with an increased ion flux density on the product 1 while heating their surface to a temperature of 200 ÷ 500 ° C. To do this, turn on the magnetron 4 power sources and bias voltages, set the magnetron discharge current on the magnetrons, bias voltage and supply a mixture of argon and nitrogen gases to the vacuum chamber 2.

Due to the bombardment of the surface of products 1 with accelerated bias voltage by argon ions, it is heated to the temperature of nitriding - 200 ÷ 500 ° C, and also etching occurs.

Ion-plasma nitriding of the surface consists in the diffusion saturation of the surface layer of metal 6 with atomic nitrogen, resulting in the formation of a solution of nitrogen in metal 6. Atomic nitrogen is formed in a magnetron discharge plasma. The hardness of the nitrided surface 7 can increase up to six times from the original value, decreasing with depth to the hardness of the starting material 6.

Carrying out ion-plasma nitriding provides a depth of the modified layer 7 of more than 70 microns. Due to the combination of ion-plasma nitriding and ion etching, the surface of the product remains light in color, free from nitride compounds with elements that make up the metal. The roughness of the nitrided surface does not exceed 0.6 μm for pre-polished samples. The formation of a nitrided layer 7 with maximum hardness in the surface region of the sample can significantly reduce mechanical stresses and prevent a sharp change in hardness at the interface between coating 8 and the main coating 9. Thus, a solid surface layer 7 is able to withstand significant mechanical stresses.

At the stage of combined ion etching and ion-plasma nitriding, magnetron 4 is used as sources of argon plasma.

Immediately after the formation of the nitrided layer 7, a coating is applied. In this case, the magnetrons 3 and 4 operate in the Hi-Power Impulse Magnetron Sputtering (HiPIMS) mode - a high-power pulsed magnetron sputtering of a target in an inert gas plasma or a mixture of inert and reaction gases. The transition coating layer of at least one layer of metal, metal carbide or metal nitride 8 is magnetically coated onto the nitrided surface 7 by magnetron 4. Since the surface is roughened after nitriding, the transition coating layer of at least one layer of metal, metal carbide or metal nitride 8 is applied in such a way as to smooth the surface before applying the base layer 9 and ensure its hardness. For this, the coating layer 8 is applied with a varying bias voltage and a varying flow of the reaction gas — nitrogen or carbon-containing gas. At the beginning of applying layer 8, the negative bias voltage is 500–600 V, and the reaction gas flow is zero,

a sublayer of pure metal is applied. Gradually, the negative bias voltage is reduced to 60-130 V, and the flow of the reaction gas is increased to form solid nitride or metal carbide, for example chromium. The application of a coating with a high bias voltage makes it possible at the initial stage to fill the hollows of a rough surface with sprayed metal, practically without coating the tops of the relief. Alignment (planarization) of the surface. The thickness of the layer 8 is 2 ÷ 5 roughness values (R _a , μm) and depends on the nature of the roughness relief. The increase in the flow of reaction gas during deposition allows you to get a coating layer 8 of gradient hardness, on which the main layer of BAM 9 is sprayed.

After the formation of the transition coating layer from at least one layer of metal, metal carbide or metal nitride 8, the magnetron 4 is turned off and the magnetron 3 is turned on, the main layer of BAM 9 is applied. The BAM material is a semiconductor with a resistivity of the order of 10 ⁴ Ohm⋅cm. For a stable magnetron discharge, a target of Al _0.75 Mg _0.75 B ₁₄ requires preliminary heating.

Preliminary heating of the target is carried out in a non-spraying pulsed magnetron discharge with a frequency of 20 kHz and a peak voltage of -1250 V. After heating the target, it becomes possible to use a spraying magnetron discharge. The main layer of VAM 9 is applied at a pulsed bias voltage applied to products 1 with the following parameters: the frequency of pulses varies from 10 to 100 kHz, the negative voltage in a pulse is 60–450 V. The magnetron sputtering of the VAM target occurs in HiPIMS mode, which allows to increase the ionic component in the stream of the sprayed target material. Spraying occurs with the following parameters: pulse repetition rate 200 ÷ 400 Hz; the power density supplied to the target in the pulse is from 40 to 100 W / cm ² . An increase in power density can lead to deformation of the target and, as a consequence, to its cracking.

The thickness of the applied layer 9 is 1 ÷ 2 μm. With an increase in the thickness of the BAM 9 layer, strong internal compressive stresses arise, which can lead to its partial detachment. The total thickness of the transition coating layer of at least one metal layer, metal carbide or metal nitride 8 and the base layer 9 is up to 3.1 μm.

Tribological coating example

The working surface of products 1, requiring hardening, is polished either mechanically by polishing pastes, or, if the material of the product allows, in electrolyte-plasma polishing. Then the products 1 are degreased in an ultrasonic bath in a solution of soap alkali, washed in running distilled water and subjected to heat treatment in an oven. After heat treatment of the product 1 is treated with nefras C1-80 / 120 and installed in the vacuum chamber 2 of the installation. In this case, the products 1 are electrically isolated from the housing of the vacuum chamber 2 and connected to a source of pulse negative voltage (bias voltage).

After installing the products 1 in the vacuum chamber 2, it closes and is pumped to a high vacuum, not less than 10 ^-4 Pa. To intensify the process of degassing the walls of the vacuum chamber 2 and the surface of the products 1 during pumping, they are heated to a temperature of not more than 170 ° C. To this end, heaters 5 (tape or heating elements) are provided in the vacuum chamber 2.

The vacuum chamber 2 is equipped with at least two magnetrons: a magnetron 3, atomizing Al _0.75 Mg _0.75 B _{14 with a} purity of at least 99.95%, and a magnetron 4, atomizing metal (or titanium with a purity of at least 99.95% , or from chrome purity of not less than 99.95%). Both magnetrons have the ability to work both in direct current mode and in HiP-IMS mode - high-power pulsed magnetron sputtering of the target.

After the pressure inside the vacuum chamber 2 10 ^-4 Pa is reached, the heating is turned off, the plasma-forming argon gas (purity not less than 99.9995%) is injected to a pressure of 0.2 ÷ 0.35 Pa and a negative voltage of 1000-H100 V is applied to the products 1. Ignited an abnormally glow discharge and ion etching of the surface of the products is carried out 1. To intensify the process of ion etching, the magnetron 4 is turned on at low power, not more than 2.5 W / cm ² . The ion etching process lasts from 30 to 50 minutes, depending on the material of the products 1.

After the process of ion etching of the surface of the articles 1, nitrogen gas (purity no less than 99.9995% o) is additionally introduced into the vacuum chamber 2 to a combined pressure (together with argon) of 0.1 ÷ 3 Pa. An impulse negative voltage of 800 ÷ 1250 V with a frequency of at least 10 kHz is supplied to the products 1 and the process of ion-plasma nitriding begins. Also, for plasma activation, magnetron 4 works with a low power density - not more than 2.5 W / cm ² . The temperature of the products 1 is maintained within 200–500 ° C by adjusting the power of the magnetron 4 power source. The nitriding time is 100 min, and the thickness of the nitrided layer 7 is approximately 70 μm.

After the formation of the surface layer of the products saturated with nitrogen 7, a transition coating layer of at least one metal layer, metal carbide or metal nitride 8 is applied. In this case, the magnetron 4 operates in a mode with an integrated power density of 20 ÷ 26 W / cm ² and a pulse repetition rate of 150 ÷ 350 Hz, and the bias voltage operates in constant current mode and gradually decreases from -600 V to -80 V. Simultaneously with a decrease in the bias voltage, the flow rate of the supplied reaction gas of nitrogen or methane increases from 0 to 1.62 l / h.

After applying a transitional coating layer of at least one layer of metal, metal carbide or metal nitride 8, the magnetron 4 is turned off, a negative voltage of 60 ÷ 150 V is applied to the product with a pulse repetition rate of 10 to 100 kHz and the magnetron 3 is turned on. The application of the main layer begins coatings 9. In this case, the magnetron 3 operates in HiPIMS mode with a frequency of 200–400 Hz and a power density supplied to the target surface in the pulse of 404 00 W / cm ² . The growth rate of the main coating layer 9 is 1 μm / h, the thickness is 1 ÷ 2 μm.

After the coating process is completed, neutral argon gas is introduced into the vacuum chamber 2 to a pressure of 300 Pa and the products 1 are cooled. At a temperature of the products 1 equal to 150 ° C, air is introduced into the vacuum chamber 2 and removed.

The tribological properties of the coating were studied using the pin-on-disk test method. The radius of curvature of the pin was 4.7625 mm, the load on the pin was 60.33 N, the path length was 1000 m, and the speed was 0.9 m / s. Microhardness was measured by the Vickers method.

The resulting tribological coating parameters are as follows:

1) The coating thickness together with the modified layer is from 74 microns to 100 microns.

2) The microhardness of the total coating composition is from 35 GPa to 40 GPa.

3) The coefficient of friction is from 0.01 to 0.07.

The use of the invention provides a reduction in the coefficient of friction (0.01 ÷ 0.07) and an increase in microhardness up to 35 ÷ 40 GPa on highly-loaded surfaces of products 1.

Claims (1)

A method of forming a tribological coating, including ion etching of the surface of the product, applying a transition coating layer of at least one layer of metal, metal carbide or metal nitride and applying the main coating layer, characterized in that the treated metal surface of the product simultaneously with ion etching is subjected to nitriding, applying the specified transition layer of the coating is carried out with time-varying negative bias voltage and the flow of the reaction gas, the flow rate of which elichivaetsya simultaneously with lowering the bias voltage, and the main coating layer is applied by means of high-power pulsed magnetron sputtering target after heating of the Al _0,75 Mg _0,75 B _14.

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