RU2416679C2 - Method of forming wear resistant galvanic metal coatings - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: method includes the application of galvanic coating made of electrolyte solution on part surface containing ferrum salt, sulphuric and hydrochloric acids. Note that the coating is applied by subsequent forming of alternating iron layers of high and low hardness of 10-30 micron thick, hardness ratio of which amounts 4-8.

EFFECT: improvement of coating wear resistance.

1 dwg, 1 ex

Description

The invention relates to the restoration of worn parts of machines and mechanisms by applying to their surface galvanic iron coatings with high wear resistance.

A known method of applying to the surface of worn parts of galvanic iron coatings with the aim of restoring their geometric dimensions and hardening the surface to be abraded during operation [1]. In this case, the restored part and the soluble anode made of low-carbon steel are placed in an electrolyte solution containing salts of iron, sodium tartaric acid, sulfuric and hydrochloric acids, and connected to a current source. Electrolysis is carried out at a constant current density until the desired coating thickness is obtained. At a cathode current density of 60-100 A / dm ^{2, the} coatings have a hardness of 50-60 HRC and high wear resistance comparable to that of hardened carbon steel.

The disadvantage of this method is the high fragility of the coating, which leads to its destruction during operation.

Closest to the proposed method is a method of forming wear-resistant composite galvanic iron coatings obtained from suspension electrolytes in the process of heteroadagration of particles of the dispersed phase at the cathode, followed by their overgrowing with an electrodeposit metal matrix [2]. Particles of the dispersed phase, in particular, are carbides, oxides, borides, nitrides having high hardness in comparison with the metal matrix of the electroplated coating. The maximum wear resistance of composite coatings is achieved when the ratio of the hardness of the particles of the dispersed phase to the hardness of the material of the metal matrix, lying in the range from 4 to 8. The size of the dispersed particles should correspond to the optimal contact area required during running-in of rubbing surfaces. Depending on the purpose of the restored part, it is 10-30 microns [2].

The disadvantages of this method are:

- the difficulty of obtaining coatings with a given concentration of the dispersed phase;

- the absence of chemical bonds between the metal matrix and particles of the dispersed phase, which in some cases leads to chipping of dispersed inclusions.

The objective of the invention is the creation of structural heterogeneity of a chemically homogeneous galvanic coating material for the subsequent formation of an analogue of a matrix of low hardness with solid inclusions.

The technical result is an increase in the wear resistance of coatings.

The result is achieved by the fact that a galvanic coating is applied to the surface of the part from an electrolyte solution containing an iron salt, sulfuric and hydrochloric acids, and then iron layers 10-30 microns thick, the hardness ratio of which is 4-8, are subsequently formed.

The coating is applied from an iron electrolyte of the following composition:

FeCl ₂ · 4H ₂ O 500 g / l Na ₂ C ₄ H ₄ O ₆ · 2H ₂ O 3 g / l H ₂ SO ₄ 2 g / l Hcl (1-2) g / l to pH = (0.8-1.2)

The temperature of the electrolyte is 50 ° C.

First, at a cathode current density of 10 A / dm ² , a coating layer with a thickness of 0.1 mm with a hardness of 7-12 HRC [3] is applied over an hour, serving as a metal matrix for the further formation of alternating layers of relatively high and low hardness. Then, layers with a hardness of 50-55 and 7-12 HRC are successively applied with a thickness of 10-30 μm each at cathodic current densities of 60-100 and 10 A / dm ^2, respectively. The application time of harder of these layers is 1-4 minutes, less hard - 6-18 minutes. In total, in the process of part restoration, 5-10 pairs of layers are formed, the hardness ratio of which is 4-8.

A galvanic coating with alternating layers of low and high hardness (“layered” coating) is similar in its properties to electroplating with solid dispersed inclusions of another phase. Since the predominant growth of the electroplated coating occurs on the microroughnesses of the relief, the solid layer formed at a high cathode current density is similar to disperse solid particles. The time of build-up of the solid layer is selected so that the size of the solid grains formed on the microroughness corresponds to the optimal particle size (10-30 μm) from the point of view of wear resistance [2]. The layer of low hardness that builds up further eliminates the chipping of the wear-resistant layer of high hardness. Alternating layers of high and low hardness make it possible to form a wear-resistant layer of considerable thickness, up to 1.5 mm.

An example of a specific implementation of the method of applying wear-resistant "layered" electroplated coatings: the coating was applied to the surface of samples made of steel 45, since a large number of automotive and other parts are made of this steel. Before coating, the samples had a diameter of 40 mm and a thickness of 8 mm. The samples were degreased by boiling in a 5% sodium hydroxide solution for ten minutes, then washed successively in running hot (60 ° C) and cold (20 ° C) water for one minute. Samples were connected to a conductive busbar. The surfaces of the substrates were insulated with dielectric washers so that coating was carried out only on a cylindrical surface. Immediately prior to coating, the samples were subjected to finish anode treatment in 35% sulfuric acid at room temperature for 30 seconds at an anode current density of 60 A / dm ² . Then, the samples were washed with a jet of hot (60 ° C) water and placed in a bath with ironing electrolyte, the composition and temperature of which are given above.

At a cathode current density of 10 A / dm ² , a coating layer 0.1 mm thick with a hardness of 7-12 HRC was applied on the cylindrical surface of the sample for an hour. Then ten pairs of layers 20 μm thick each were sequentially deposited at a cathode current density of 100 and 10 A / dm ² and hardness of 50-55 and 7-12 HRC, respectively. The application time of the harder of these layers is 1.5 minutes, less than hard 15 minutes. After grinding to a depth of 0.1 mm, the wear resistance of the samples on the SMTS-2 machine was determined.

The results of comparative tests of the wear value of "layered" coatings obtained by the proposed method, and control, applied under the same conditions at a constant cathode current density of 20 A / DM ² are shown in the drawing. Test conditions: block - AMKO-8-1-3, travel speed 3.14 m / s, test time 1 hour, lubrication - mineral oil M10G2. It can be seen that the wear rate of “layered” coatings is approximately 30% less than the control value.

Thus, it has been experimentally established that the formation of “layered” coatings by the above means and methods allows to achieve a technical result: an increase in wear resistance by about 30%.

Information sources

1. Melkov M.P., Shevtsov A.N., Melkova I.M. Restoring automotive parts with hard iron. - M .: Transport, 1982. - 198 S.

2. Guryanov G.V. Electrodeposition of wear resistant compositions. Chisinau: STIINZA, 1985 .-- 238 S.

3. Ivashkin Yu.A., Kovalenko L.V., Potapenkov E.V. Hardness and wear resistance of galvanic iron-nickel coatings. - Repair, restoration, modernization, 2006, No. 3, p.41-42.

Claims (1)

A method of forming wear-resistant galvanic iron coatings, comprising applying to the surface of a part a galvanic coating from an electrolyte solution containing an iron salt, sulfuric and hydrochloric acid, characterized in that the coating is applied by sequential formation of alternating layers of high and low hardness with a thickness of 10-30 μm, hardness ratio which is 4-8.

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