RU2791115C1 - Method for deposition of a wear-resistant cobalt-chromium coating on aluminum alloy substrates - Google Patents

Abstract

FIELD: wear-resistant cobalt-chromium coatings.

SUBSTANCE: nvention relates to a method for producing a wear-resistant cobalt-chromium coating on an aluminum alloy substrate. An intermediate layer of cobalt coating is applied with a thickness of 1 to 2 µm on the surface of an aluminum alloy substrate heated to a temperature of 390 to 410°C by feeding cobalt nitrosyltricarbonyl vapor into the reactor at a temperature of 18 to 23°C, at a rate of 1 to 2 l/h, at a residual pressure in the reactor of 10 to 20 Pa, in an environment of argon carrier gas and thermal decomposition of cobalt nitrosyltricarbonyl vapor. Then, vapors of chromium hexacarbonyl are fed into the reactor at a temperature of 35 to 45°C, at a rate of 1 to 2 l/h, in an argon carrier gas medium. Vapors of chromium hexacarbonyl thermally decompose to provide a wear-resistant cobalt-chromium coating with a thickness of 1.0 to 1.5 microns on an aluminum alloy substrate.

EFFECT: increased wear resistance of the coated substrate.

1 cl, 5 ex, 2 tbl

Description

The invention relates to the field of obtaining wear-resistant combined metal coatings, in particular, cobalt-chromium, on aluminum alloy substrates by thermal decomposition of cobalt nitrosyltricarbonyl and chromium hexacarbonyl and can be used for coating when hardening parts made of aluminum alloys, working in conjunction with parts made of structural steels, emergency, road construction, tillage, agricultural, logging machines.

A known method of deposition of a protective two-layer coating, consisting of a sublayer of chromium and chromium carbide, on long metal products. This coating is obtained by pyrolytic decomposition of the vapors of the organochromic liquid "Barkhos" and is applied during the translational movement of the product through two deposition zones: the temperature of the first zone is 340-360 ° C, the second - 540-560 ° C (RU, No. 2169793, C23C 16/18 , 2001).

However, this method is characterized by the impossibility of depositing a protective coating on parts of a geometric shape other than pipes and cylinders, as well as the complexity of technical execution.

A known method of applying a wear-resistant composite layered coating by thermal decomposition of vapors of carbonyls of metals VI-VIII groups of the Periodic system at reduced pressure, in which the first layer 3-5 μm thick is applied using carbonyls of metals VI-VIII groups at a temperature of 600-900 ° C, pressure 0 .5-1.0 mmHg (67-133 Pa) and a growth rate of 1-2 μm/min, and a second layer of the same thickness is applied at a temperature of 300-450°C using group VI-VII metal carbonyls, a pressure of not more than 0.5 mm Hg. (67 Pa) and a coating growth rate of 0.3-0.5 µm/min (RU, No. 2075540, C23C 16/16, 1997).

However, in this method, it is impossible to carry out the deposition of a hardening coating on aluminum alloy substrates.

A known method of applying a chemically resistant non-porous protective coating on the surface of an aluminum flange by thermal decomposition of organometallic chromium compounds in vacuum at a pressure of 1-10 Pa and a temperature of 400-450°C (RU, No. 2433210, C23C 16/18, C23C 4/08, 2011) .

However, this method is characterized by high stresses in the matrix-coating system and insufficient adhesion.

A known method of obtaining a composite coating on aluminum or its alloys, containing an intermediate layer of oxide ceramics (Al ₂ O ₃ ) with a thickness of 50-300 microns, obtained by microarc oxidation, and a layer of pyrolytic chromium carbide with a thickness of 5-50 microns, deposited during the pyrolysis of a bisarene-chromium-organic compound (RU, No. 2175686, С23С 28/00, 2001).

However, in this method it is impossible to obtain a high-quality oxide film on aluminum alloys with a high silicon content, since a large amount of SiO ₂ particles are formed during the oxidation of such alloys, which prevent further deposition of the pyrolytic chromium carbide coating.

The closest in technical essence is the method of deposition of a wear-resistant coating on an aluminum alloy, in which an intermediate layer is formed, followed by the deposition of a layer of chromium carbide on it by chemical vapor deposition of a bisarenechromoorganic compound at a temperature of 450-480 ° C and a pressure of ≤ 100 Pa in an inert flow. gas, while the intermediate layer is formed from a nickel-cobalt alloy by an electrochemical method (RU, No. 2569199, С23С 28/00, С23С 16/28, C25D 3/12, 2015).

However, the impossibility of obtaining a complex wear-resistant coating with a uniform thickness of the metal layer up to 5 microns by one method of metallization complicates the process technically, and also reduces its economic efficiency.

The technical objective of the invention is to develop a method for obtaining a cobalt-chromium coating used to harden parts made of aluminum alloys, working in conjunction with parts made of structural steels, emergency rescue, road construction, tillage, agricultural, logging machines in the conditions of repair enterprises.

The technical result of the invention is to increase wear resistance and increase the resource of the assembly unit.

The task and the technical result are achieved by the fact that in the method for obtaining a wear-resistant cobalt-chromium coating on an aluminum alloy substrate, including the deposition of an intermediate cobalt layer on the surface of a heated aluminum alloy substrate in the reactor, while the intermediate cobalt coating layer is applied with a thickness of 1 to 2 µm onto the surface of an aluminum alloy substrate heated to a temperature of 390 to 410°C by feeding vapors of cobalt nitrosyltricarbonyl at a temperature of 18 to 23°C into the reactor at a rate of 1 to 2 l/h, at a residual pressure in the reactor of 10 to 20 Pa, in an argon carrier gas medium, which is fed into the reactor at a rate of 55 to 65 l / h, and thermal decomposition of cobalt nitrosyl tricarbonyl vapor, then chromium hexacarbonyl vapor is fed into the reactor at a temperature of 35 to 45 ° C, at a rate of from 1 to 2 l/h, in an argon carrier gas medium, which is fed into the reactor at a rate of 55 to 65 l/h, while chromium hexacarbonyl vapor and thermally decompose to provide a wear-resistant cobalt-chromium coating with a thickness of 1.0 to 1.5 μm on an aluminum alloy substrate.

The deposition of an intermediate layer of cobalt coating in an argon environment in the indicated metallization modes (substrate temperature, cobalt nitrosyltricarbonyl vapor temperature) ensures the minimum value of residual stresses in the “cobalt coating layer - aluminum substrate” system due to the formation of a coating with a low content of impurities of the oxide and carbide phases.

The temperature conditions for heating vapors of cobalt nitrosyltricarbonyl, chromium hexacarbonyl and the substrate were determined by studying the thermodynamics of chemical reactions of thermal decomposition of organometallic compounds to ensure the stability of the morphostructural characteristics and chemical composition of the metal coating. A change in the ratio of the heating temperatures of cobalt nitrosyltricarbonyl vapor, chromium hexacarbonyl vapor and the substrate, the feed rate of the initial reagents into the reaction chamber at the stages of formation of the intermediate layer of the cobalt coating and deposition of the main layer of the cobalt-chromium coating leads to a violation of the mechanisms of interaction between the vapors of the initial reagents and the substrate, the formation of defects in the structure coatings.

Increasing the temperature of the vapors of the initial reagents leads to the need to increase the rate of supply of their vapors into the working chamber of the coating apparatus (reactor) to provide the required growth rate and coating thickness.

Lowering the temperature of the vapors of the initial reagents leads to a decrease in the growth rate of coatings, an increase in the likelihood of side reactions, the products of which are impurity components in the form of free carbon, carbides, and metal oxides, a high concentration of which destabilizes the system, causing delamination of the metal from the substrate surface.

An increase in the substrate heating temperature promotes overheating of the reaction gas, which leads to premature decomposition of the starting compounds in the reactor volume with the release of metal particles. At a substrate temperature of more than 450°C, the growth rate of the metal coating stops, the reagents decompose in the reactor volume, not reaching the substrate.

At a substrate temperature below 300°C, the metal coating growth process is determined mainly by the rate of decomposition reactions of the initial reagents, affecting the surface morphology and the internal structure of the coatings by the formation of large spherical metal formations and an increased concentration of impurities at the grain boundaries.

The replacement of an inert carrier gas (argon) by carbon monoxide leads to the formation of defects in the coating structure.

The application of the main layer of the cobalt-chromium coating by supplying vapors of chromium hexacarbonyl in an argon medium, heated to a temperature of 35 to 45°C, onto the substrate creates technological possibilities for obtaining a complex coating layer with a high content of chromium carbide of the required microhardness and thickness on the working surface of the part.

Sequential thermal decomposition of cobalt nitrosyltricarbonyl and chromium hexacarbonyl in one metallization cycle promotes diffusion saturation of the coating (intermediate and main layer) with cobalt and chromium, ensuring the homogeneity of the structure and chemical composition of the coating.

The essence of the invention is illustrated by the following examples.

Example 1

In the working chamber of the coating apparatus (reactor), the bearings of the NSh-50U gear pumps were mounted, the vacuum pump was turned on, and a residual pressure of 10 Pa was created in the reactor. Next, the system was purged with argon through the flowmeter, the flow rate was 60 l/h. The item was heated to a temperature of 400°C. Then, cobalt nitrosyl tricarbonyl vapors heated to a temperature of 20°C were introduced from the evaporator through a flow meter into the reactor at a rate of 1.5 l/h, and a coating layer up to 2 μm thick was deposited within 5 minutes. Further, the supply of cobalt nitrosyltricarbonyl vapors was stopped. Chromium hexacarbonyl vapor heated to a temperature of 40°C was fed from the sublimator through a flow meter into the reactor at a rate of 1.5 l/h, and a layer of cobalt-chromium coating up to 1.5 μm thick was deposited within 3 minutes. Then the supply of vapors of chromium hexacarbonyl and argon was stopped, the heater was turned off, and the parts were held for 10 minutes in order to cool them. Then the parts were dismantled.

The study of the quality of the obtained coatings on the cut was carried out using a two-beam system (small dual beam, FIB/SEM) in a Quanta 3D FEG scanning electron microscope; The elemental composition of the coatings was determined by energy-dispersive X-ray spectroscopy. The study to determine the microhardness was carried out on samples in accordance with GOST 9450-76 "Measurement of microhardness by indentation of diamond tips." The adhesion strength of the resulting coatings to the substrate was determined by the pin method on an FP-10/1 testing machine. The surface roughness of the coatings was measured by probing using a MarSurf PS1 profilometer. The study of wear resistance in bench tests was carried out on a testing machine model SMTs-2 with samples of the "disk-block" type. Cobalt-chromium coatings were applied to the surface of a disk made of aluminum alloy AK9M2 GOST 1583-93, the block was made of steel 18KhGT GOST 4543-71, hardened to HRC 58–62. We also studied the wear resistance of the “plain bearing-shaft pin” interface of gear pumps NSh-50U. Industrial oil I20 GOST 20779-75 was used as a working fluid. To ensure accelerated wear, an abrasive prepared from GOST 2138-84 quartz molding sand with a fineness of 3 μm was added to the working fluid. The content of the abrasive material in the working fluid was 3±0.5% by weight of the oil.

Technological modes of conducting metallization are presented in table 1. The properties of the resulting coating are shown in table 2.

Example 2

The example was carried out similarly to the example above, but the heating temperature of the part was reduced to 350°C. The formed coating had a vertical columnar structure. There was a decrease in the adhesion strength of the coating to the substrate to 60 MPa, and in the process of bench testing of samples of the "disk-block" type, the coating peeled off from the surface of the sample.

Technological modes of conducting metallization are presented in table 1. The properties of the resulting coating are shown in table 2.

Example 3

The example was carried out similarly to the above example 1, but the heating temperature of the part was increased to 450°C. This led to a decrease in the coating growth rate due to heating of the medium around the substrate and dissociation of the initial reagents in the reactor volume. There was a release of highly dispersed carbon in the volume of the reactor and on the surface of the substrate. A coating with a vertical columnar structure was formed, the surface morphology of the samples is highly dispersed, “granular”, containing defects in the form of pores with inclusions of soot particles. There was a decrease in the adhesion strength of the coating with the substrate to 40 MPa, as well as a decrease in the microhardness of the coating to 14 GPa.

Technological modes of conducting metallization are presented in table 1. The properties of the resulting coating are shown in table 2.

Example 4

The example was carried out similarly to Example 1 above, but the chromium hexacarbonyl vapor feed rate to the reactor was reduced to 1.0 l/h. This led to a decrease in the coating growth rate and the formation of a metal layer with a thickness of less than 2 μm. There was a decrease in the microhardness of the coating to 16 GPa, the adhesion strength of the coating to the substrate - up to 70 MPa.

Technological modes of conducting metallization are presented in table 1. The properties of the resulting coating are shown in table 2.

Example 5

The example was carried out similarly to the above example 1, but the plating was carried out in a carbon monoxide environment. This contributed to the formation of cobalt oxides in the intermediate coating layer and the formation of an oxide film on the surface, which led to an increase in the number of defects at the interface "aluminum substrate - intermediate coating layer" and to a decrease in the adhesion strength of the coating to the substrate to 30 MPa. The microhardness of the coating decreased to 12 GPa.

Technological modes of conducting metallization are presented in table 1. The properties of the resulting coating are shown in table 2.

The proposed method for applying a cobalt-chromium coating on aluminum alloy substrates is effective in achieving an optimal combination of wear values in friction pairs (0.15–0.20 g), microhardness 17–18 GPa, adhesion strength 80–90 MPa, and roughness ( Ra = 0.16-0.32 μm) of the obtained coatings with a substrate, which provides an increase in the wear resistance of parts by a factor of 2.0-2.5 compared to mass-produced parts.

The present invention is at the stage of laboratory research tests.

Claims (1)

A method for producing a wear-resistant cobalt-chromium coating on an aluminum alloy substrate, which includes applying an intermediate cobalt layer on the surface of a heated aluminum alloy substrate in a reactor, characterized in that the intermediate cobalt coating layer is applied with a thickness of 1 to 2 μm on the surface of an aluminum alloy substrate, heated to a temperature of 390 to 410°C, by supplying vapors of cobalt nitrosyl tricarbonyl to the reactor at a temperature of 18 to 23°C, at a rate of 1 to 2 l/h, at a residual pressure in the reactor of 10 to 20 Pa, in a carrier medium argon gas, which is fed into the reactor at a rate of 55 to 65 l / h, and thermal decomposition of cobalt nitrosyl tricarbonyl vapor, then chromium hexacarbonyl vapor is fed into the reactor at a temperature of 35 to 45 ° C, at a rate of 1 to 2 l / h, in an argon carrier gas medium, which is fed into the reactor at a rate of 55 to 65 l/h, while chromium hexacarbonyl vapors thermally decompose to ensure wear resistant cobalt-chromium coating with a thickness of 1.0 to 1.5 microns on an aluminum alloy substrate.