RU2513496C2 - Chromium-based wearproof metal coating and method of its application - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to obtaining coatings by method of chemical sedimentation from gas phase, namely to obtaining protective coatings from chromium and its alloys. Method of application of chromium-based wearproof metal coating includes supply of steam-gas mixture, which contains bis-arene compound of chromium and volatile compound of tin to the surface of heated product in vacuum, as volatile compound of tin applied is 0.1-1.0% tin tetrachloride, and process is carried out at temperature of heated product from 350 to 400 °C. Wearproof chromium-based metal coating contains modifying tin additive, has multi-layer structure from sequentially placed layers based on chromium with modifying tin additive, enriched and depleted of carbon. In depleted of carbon layers content of carbon is 0.5-5.0%, and in enriched with carbon layers - 6.0-12.0%.

EFFECT: increased wear stability of coatings is ensured, which makes it possible to improve tribological characteristics of engine details.

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Description

The invention relates to the field of production of chromium-based metal coatings by chemical vapor deposition (CVD method) and can be used to increase wear resistance and improve tribological characteristics (reduce friction coefficient) of engine parts, for example, piston-cylinder elements.

Known methods for applying protective metal coatings based on chromium using bis-arene compounds of chromium [B. G. Gribov, G.A. Domrachev, B.V. Beetle et al., Precipitation of films and coatings by decomposition of organometallic compounds. M .; Science, 1981]. The process is carried out by supplying vapor of bis-arene compounds of chromium to the surface of the product at a temperature of 350-600 ° C with the constant removal of gaseous decomposition products from the deposition zone. Coatings combine valuable qualities: high hardness, corrosion resistance and are used to protect machine parts from wear, chemical corrosion and reduce friction. The main problem in the practical application of these coatings is a high level of stress in the coating, and therefore, peeling or cracking of the coating can occur at a certain coating thickness. A technical solution is known to reduce the level of internal stresses of coatings by using additives of halogen and sulfur compounds [US Patent 3372055, May 18, 1965]. However, the carbon content in the coating is reduced, which leads to a decrease in corrosion resistance and microhardness. Also known is a coating method based on a pulsed feed of a solution of a bis-arene chromium compound in an organic solvent [US Patent Application 20090324822, July 19, 2007]. Its disadvantage is low productivity and high consumption of organic solvents. A known method of coating at a product temperature of 200-300 ° C in vacuum using a bis-arene chromium compound, which additionally contains from 1 to 15% volatile tetraalkyl tin compound [Russian Patent 1453950, 06/16/1993]. The resulting coatings contain from 1 to 15% tin and are characterized by high corrosion resistance. The speed of the coating according to the patent can be up to 1.5 μm / min. This invention is the closest to the claimed and we have chosen as a prototype. The disadvantages of the coating is a relatively low microhardness (10-13 GPa) and low adhesion of the coating (25-30 MPa). In addition, toxic and explosive tin alkyl compounds are used in the process.

The objective of the present invention is to remedy these disadvantages, and, above all, to increase the adhesion and microhardness of the coating while maintaining a low level of internal stresses.

The technical result of the invention is to improve the quality of coatings by increasing their wear resistance.

The technical result is achieved by the fact that in the known method of applying a wear-resistant chromium-based metal coating, comprising supplying a vapor-gas mixture containing a bis-arene chromium compound and a volatile tin compound to the surface of a heated product in vacuum, the gas-vapor mixture contains tin tetrachloride as a volatile compound with its content in the mixture of 0.1-1.0%, and the process is carried out at a temperature of the heated product from 350 ° to 400 ° C.

The coating formed under these conditions has a multilayer structure consisting of successive chromium-based layers with tin modifying additive, with a carbon content of 0.5-5% in carbon-depleted layers and 6.0-12.0% in carbon-enriched layers . The thickness of successive layers is from 0.05 to 1.5 microns.

As a bis-arene chromium compound, chromium compounds of the general formula are used: {[C ₆ H _6-x (CnH ₂ n ₊₁ ) _x ] [C ₆ H _6-y (C _m H ₂ m ₊₁ ) _y ]} Cr , where x, y = 0, 1, 2, and n, m = 1, 2, 3 or their mixtures, which can be synthesized by known methods [Brauer G. (ed.) Guide to inorganic synthesis. Volume 5. M .: Mir, 1985. 360 pp.] Or a similar technical product “Barchos” [TU 6-01-1149-78, TU 2436-020-52470175-2003].

A gas-vapor mixture is prepared by dissolving at room temperature anhydrous tin chloride with a chemical purity of at least 95% in a bis-arene chromium compound in the required ratio and then evaporating the resulting mixture by feeding it to an evaporator heated to a temperature of 150-250 ° C.

The process can be carried out in the installation, the diagram of which is presented in figure 1. On this scheme of the pilot plant it is indicated: 1 - reaction chamber, 2 - products (rings on the mandrel), 3 - deposition zone, 4 - dispenser, 5 - feeder, 6 - evaporator, 7 - mechanical vacuum pump, 8 - steam-oil booster a pump, 9 - a nitrogen trap, 10 - a water-cooled trap, 11, 12 - containers for discharging organic waste, 13 - an electric drive. The main working unit of the installation is a horizontal reaction chamber 1. The deposition process of the coating is as follows. Covered products are fixed in the holder 2. The chamber is closed and vacuum. Turn on the heating and warm the product to operating temperature. The drive 13 is turned on and the products are passed through the deposition zone in rotational and translational motion. At the same time, the supply of the working mixture of the bis-arene compound of chromium and tin tetrachloride from dispenser 4 to the evaporator 6 located above the products begins. The vapor-gas mixture from the evaporator 6 enters the surface of the products and decomposes with the formation of a solid phase of the coating and gaseous reaction products. Gaseous products are removed from the chamber using vacuum pumps 7 and 8. The vacuum in the chamber is monitored using a VT-3 vacuum gauge, the heating temperature is controlled by a thermocouple sensor and maintained in a predetermined mode by the control system.

The result is a wear-resistant chromium-based metal coating containing a tin modifying additive. The resulting coating has a multilayer structure containing successive layers enriched and depleted in carbon. The carbon content in successive layers is from 0.5 to 5% in carbon depleted layers and from 6 to 12% in carbon-rich layers, and the thickness of successive layers is from 0.05 to 1.5 μm. The invention is illustrated by the following examples. Example 1. As an initial bis-arene compound of chromium, the Barchos organochromic liquid was used (TU 6-01-1149-78). For the preparation of the working mixture used tin tetrachloride brand h.ch. The working mixture was prepared by dissolving 2 ml (~ 5 g) of tin tetrachloride in 450 ml (~ 530 g) of Barchos organochromic liquid. As simulators for coating, we used flat simulators made of cast iron of the СЧХН brand, 08ХН10Т stainless steel, and 15X tool steel with dimensions of 30 × 20 × 1 mm and with surface cleanliness in the range Ra = 0.15-l, 25 μm. Preparation of the products for coating included degreasing in an ammonia solution in an ultrasonic bath, washing and drying. Dried items are fixed in the holder (2, Figure 1). The holder with products through a lock device is loaded into the metallization chamber. The chamber is evacuated to a residual pressure of ~ 5 Pa. Products in the heating zone are heated to a temperature of 380 ± 5 ° C. The working mixture of chromium-organic liquid “BARCHOS” and tin tetrachloride (the content in the mixture is 0.94%) from a special container enters the reaction chamber with a dosing device at a rate of 80 ± 5 ml / hour. It evaporates. The gas-vapor mixture enters the surface of the heated products, where thermal decomposition occurs with the release of chromium-carbon coating. Working pressure is 25 ± 10 Pa. Volatile organic decomposition products are removed by a vacuum system where they condense in refrigerated traps. Precipitation time is 15 minutes. To stop the process, turn off the heating and after cooling the chamber produce unloading. The gravimetric method found that the coating thickness was 20 ± 2 μm. The coating rate was about 1.3 μm / min.

The resulting coatings have a mirror metallic appearance, are “X-ray amorphous” and show horizontally layered structure on metallographic thin sections (without etching). The layers are parallel to the substrate. Typical surface morphology and microstructure of the coating are presented in figure 2. The relief of the coating surface is domed, smooth, with individual spheroidal globules. On transverse sections, two types of layers are optically distinguished: white and dark. Light layers have maximum thickness, while dark layers are thinner layers. Layer-by-layer analysis (KAMEBAX electron probe microanalyzer) of the chromium content in the layers showed that in the white layers the carbon content is from 0.5 to 5%, in the dark layers from 6 to 12%.

The microhardness of PCCP on a cast iron substrate was 16.5 ± 2 GPa (PMT-3 microhardness tester, load 50 g). Studies to determine the adhesion of coatings were carried out by the normal separation method. The data obtained are presented in table 1.

Table 1. The results of determination of adhesion by the method of normal separation. Backing material PCHP thickness, microns Adhesion PKHP, MPa Nature of destruction Cast iron 12 ± 2 More than 100 Adhesive Tear Steel 15X 12 ± 2 More than 100 Adhesive Tear Stainless steel 08XH10T 20 ± 2 80-100 Tear Off Quartz plate (disk) 50 mm 15 ± 2 80-100 Tear Off

Example 2. The working mixture was prepared by dissolving 5 ml (~ 12 g) of tin tetrachloride in 2 l (~ 2.3 kg) of the Barchos organochromic liquid. Compression and oil scraper rings for 10D100 diesel engines with a diameter of 215 mm (D100.04-018; D100.04-016-2; D100.04-017-2) were used as product samples. Simultaneously with the piston rings, cylindrical imitators made of ring material (cast iron SCHHN) were chrome plated with dimensions: diameter 12 mm, length 45 mm. Preparation of the products for coating included degreasing in an ammonia solution in an ultrasonic bath, washing and drying. Coating Deposition Conditions:

- preliminary rarefaction (pressure in the reaction chamber), Pa - 1-5;

- temperature of products in the heating zone, ° C-375 ± 5;

- temperature of products in the deposition zone, final, ° C-350 ± 5;

- operating pressure. Pa - 50 ± 10;

- feed rate of the MOS "Barhos", ml / hour - 50 ± 5;

- deposition time, min - 10.

Under these conditions, coatings with a thickness of 5 ± 0.5 μm were obtained on the products. The surface relief is smooth. The coatings had a matte-mirror appearance with separate light golden areas on the end surface of the rings. The average coating growth rate was ~ 0.50-0.6 μm / min.

The microhardness of the coatings on cast iron simulators was 14–16 GPa.

The appearance of the coated products is shown in figure 3.

Tribological studies of the frictional properties of the coatings were carried out on an SMT-1 friction machine with a load of 2 MPa at a sliding speed of 1-6 m / s. Coefficient of sliding friction of coatings paired with cast iron SCHHNMD (preparation-grinding) was 0.04-0.06.

Specific process conditions and some achieved results are presented in table 2.

From the above data it follows that a decrease in the content of tin tetrachloride in the working mixture below the declared limit (0.1%) is accompanied by a sharp drop in the process speed (see lines 4 and 6 of table 2). An increase in its concentration above 1% leads to a decrease in the microhardness of the coatings (see row 7 of table 2). Carrying out the process at a product temperature above 400 ° C leads to a sharp decrease in adhesion: the coating cracks and peels off with a slight tearing force (see line 8 of table 2). Obtained according to the invention, the coatings have high mechanical strength and significant microhardness (14-18 GPa instead of 10-13 GPa according to the prototype). The adhesion of the coatings is more than 100 MPA instead of 25-30 for the prototype. The resulting coatings have high corrosion resistance: their dissolution rate in 12 N hydrochloric acid does not exceed 0.003 mg / cm ² · h, and in 12 N sulfuric acid less than 0.001 mg / cm ² · h. According to these characteristics of the coating are not inferior to the characteristics of the coating of the prototype.

The coatings obtained according to this invention do not exhibit peeling and cracking, including under conditions of thermal shock, friction and abrasive wear.

Thus, the obtained multilayer chromium-carbon coatings according to this invention have advantages in comparison with coatings of the prototype and other known technical solutions for a range of operational characteristics: microhardness, mechanical strength, adhesion and friction coefficient. Therefore, they can be successfully used in various fields of engineering, primarily to increase wear resistance and reduce the cost of friction in engines. The simplicity and efficiency of the process indicates the technical and economic advantages of the proposed gas mixture in comparison with the known solutions of the same problem.

Execution examples

№№ Process conditions Coating Properties Product Material Product temperature, ° C System pressure during deposition, Pa Chrome bis arene compound The content of tin tetrachloride,% The feed rate of the mixture, ml / h The duration of deposition, min Thickness, microns Microhardness, GPa Adhesion, MPa The content of tin,% Carbon content in enrichment / both days. layer,% one Example 1 above 380 25 Barhos 0.94 80 fifteen twenty 16.5 80-100 0.7 2/10 2 Example 2 above 375 fifty Barhos 0.52 fifty 10 5 14-16 0 0.3 4/10 3 Steel 15X 320 fifty (C ₂ H ₅ -C ₆ H ₅ ) ₂ Cr 1,0 60 twenty ~ 0.05 - - - - four Cast iron 350 fifty - "- 0.06 55 fifteen ~ 0.5 - - - - 5 Stainless Steel 08X10T 350 25 Barhos 5 75 5 10 10 thirty ~ 3 0,5 / 5 6 Cast iron 380 25 - "- 0.06 60 twenty ~ 0.5 - - - - 7 Stainless Steel 08XH10T 380 fifty - "- 1,5 fifty 10 fifteen 13 fifty one 1/8 8 Steel 15X 450 fifty - "- 0.5 55 5 10 twenty <5 0.2 2/12 9 Cast iron 400 fifty - "- 0.5 90 5 17 eighteen > 0.3 5/12 10 Cast iron 320 fifty - "- 0.9 55 10 ~ 1 - - - - eleven Cast iron 390 fifty - "- 0.7 60 10 12 eighteen > 100 0.5 2/10

Claims (3)

1. The method of applying a wear-resistant chromium-based metal coating, comprising supplying a vapor-gas mixture containing a bis-arene chromium compound and a volatile tin compound to the surface of a heated product in a vacuum, characterized in that tin tetrachloride with its content in the mixture is used as a volatile tin compound 0.1-1.0%, and the process is carried out at a temperature of the heated product from 350 to 400 ° C. 2. A wear-resistant chromium-based metal coating containing a tin modifying additive, characterized in that it is deposited by the method according to claim 1 and has a multilayer structure of successive layers based on chromium with a tin modifying additive, enriched and depleted in carbon, and in depleted layers contains 0.5-5.0% carbon, and in the enriched layers - 6.0-12.0%. 3. The wear-resistant metal coating according to claim 2, characterized in that the thickness of the successive layers is from 0.05 to 1.5 microns.

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