RU2537686C1 - Method of electrolytic precipitation of iron-molybdenum disulfide coating - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes precipitation from electrolyte, containing, kg/m³: ferrous sulfate 400-600, molybdenum disulfide 100-200, hydrochloric acid 0.5-1.5, on asymmetric alternating current with asymmetry coefficient β=1.2-6.0 and cathode density 20-80 A/dm² with mechanical mixing of electrolyte with temperature 20-40°C and acidity pH 0.8-1.0.

EFFECT: increase of process productivity due to application of asymmetric alternating current and increase of coating wear resistance due to increase of composite component of molybdenum disulfide in coating.

Description

The invention relates to the field of electrolytic deposition of hard, wear-resistant coatings, in particular composite molybdenum iron-disulfide coatings used to restore and harden the surfaces of parts.

A known method of electrolytic deposition of iron-based alloys from a chloride electrolyte containing 200-250 g / l of ferric chloride and 2-3 g / l of hydrochloric acid, alloying elements (Melkov MP Solid cooling of automotive parts. M., "Transport" , 1971, pp. 19-20). The electrolyte operates at a temperature of 60-80 ° C and provides coatings with a microhardness value of 4000-6500 MPa.

The disadvantages of this method are the high temperature and obtaining coatings with low microhardness and wear resistance of the surface.

The prototype is a well-known method of electrolytic deposition of a coating from an electrolyte containing: iron chloride 200 kg / m ³ , potassium iodide 20 kg / m ³ , sulfuric acid 0.6 kg / m ³ and molybdenum disulfide. The process is conducted with direct current at a cathodic current density of 10 A / dm ² , at an acid pH of 3.0 and an electrolyte temperature of 40 ° C (Borodin I.N. Hardening of parts with composite coatings. M., MECHANICAL ENGINEERING, 1982, p. 7-13).

The disadvantages of this method are the low productivity and low content of the composite component-molybdenum disulfide of 1.2-1.5%, which entails an increase in the friction coefficient and, as a consequence, a decrease in wear resistance.

An object of the invention is:

- an increase in the productivity of the method, which is achieved by using an alternating asymmetric current. This allows you to conduct the process at higher current densities, which, according to the Faraday law, increases the productivity of the process;

- increase the wear resistance of the coating by increasing the content of the composite component of the molybdenum disulfide to 5%. This is due to the fact that a layer of solid lubricant appears on the surface, which, in turn, reduces the coefficient of friction and increases wear resistance.

Effect: increasing the productivity of the process, through the use of alternating asymmetric current; increased wear resistance of the coating, by increasing the composite component of molybdenum disulfide in the coating up to 5%.

A method is proposed for electrolytic deposition of a coating of molybdenum iron disulfide, which incorporates up to 5% molybdenum disulfide. The resulting coatings have high adhesion to the base, high microhardness and wear resistance. Precipitation occurs from an electrolyte containing iron chloride (II), hydrochloric acid in the following ratio of components, kg / m ³ :

iron sulfate 400-600 hydrochloric acid 0.5-1.5 molybdenum disulfide 100-200

The use of iron sulfate is due to the greater stability of the electrolyte during the deposition process.

Electrodeposition is carried out at a temperature of 20-40 ° C with alternating asymmetric current with an interval of cathode current densities of 20-80 A / dm ² with an asymmetry coefficient β = 1.2-6 and mechanical mixing of the electrolyte. The acidity of the electrolyte is in the range of pH 0.8-1.0.

The electrolyte is obtained by combining an aqueous solution of iron chloride and a composite molybdenum disulfide powder.

Molybdenum disulfide is in the range of 100-200 kg / m ³ . The lower limit is due to the fact that when the content is less than 100 kg / m ³ molybdenum disulfide there is no noticeable change in the physico-mechanical properties of the coating. The upper limit is limited to a molybdenum disulfide content of 200 kg / m ³ . When the composite content is more than 200 kg / m ³ there is no significant increase in the coating itself, which makes its use economically disadvantageous.

The concentration of iron sulfate is in the range of 400-600 kg / m ³ . The lower limit indicates the zone of minimum viscosity. The upper limit indicates the zone of maximum electrical conductivity. The concentration of iron sulfate is in the range of 400-600 kg / m ³ . The lower limit indicates the zone of minimum viscosity. The upper limit shows the zone of maximum wettability of the electrodeposition surface and the maximum solubility of iron sulfate.

The content of hydrochloric acid is in the range of 0.5-1.5 kg / m ³ . The upper limit is set for economic reasons, the electrodeposition of iron at the cathode occurs with the simultaneous discharge of hydrogen. With an increase in the content of hydrochloric acid, the amount of discharging hydrogen sharply increases and the current efficiency decreases. The lower limit is selected according to the qualitative characteristics of the structures of electrolytic iron. When the content of hydrochloric acid is less than 0.5 kg / m ³ there is a strong alkalization of the cathode layer. Hydroxide formed in the cathode layer is included in the coating and this worsens its structure.

The temperature range is between 20-40 ° C. The lower limit is limited by the diffusion properties of the electrolyte. The ion motion is slow and the deposition rate of the coating is low. Above 40 ° C, the use of electrolyte is disadvantageous from an economic point of view.

A qualitative change in the coating does not occur, but the cost of heating the electrolyte increases.

The cathodic current density is in the range of 20-80 A / dm ² . Below 20 A / dm ² the current density is not advisable to use, because The electrolysis process has a low coating deposition rate. At a cathodic current density above 80 A / dm ² , strong dendritic formation occurs and the current efficiency decreases sharply.

The beginning of coating deposition takes place with an asymmetry coefficient β = 1.2, which provides high adhesion of the coating to the substrate, Gst = 350 MPa. If the asymmetry coefficient is lower than 1.2, precipitation does not occur. In the process of electrodeposition, the asymmetry coefficient is gradually increased to β = 6, which is characterized by a high and stable deposition rate of the coating. A further increase in the asymmetry coefficient is not recommended, because with a further decrease in the anode component, the process switches to a mode close to constant current, and the quality of the coatings deteriorates. Due to the different values of the asymmetry coefficient, it is possible to obtain coatings with various physical and mechanical properties.

In order for the composite to be constantly in suspension, continuous mixing of the electrolyte with a mixer with a lower location is used.

Based on the tests, the rational conditions of the method of electrodeposition of an alloy of iron-molybdenum disulfide are the conditions given in the example:

The electrolyte consists of the following components in quantities, kg / m ³ :

iron sulfate 500 molybdenum disulfide 150 hydrochloric acid 1,0

The process of electrolytic deposition of the coating is carried out at a temperature of 40 ° C and a cathodic current density of 50 A / DM ² . The deposition process begins with β = 1.2 and is gradually increased to β = 6 over 3-5 minutes. Mixing of the electrolyte occurs with a mixer with a lower arrangement. The coating has Gst = 350 MPa, the microhardness is Hµ = 7000 MPa, the deposition rate is 0.45 mm / h, the molybdenum disulfide content in the coating is 5%, the friction coefficient, compared with electrolytic iron, decreased from 0.2 to 0.14.

The proposed method has high performance due to the use of alternating asymmetric current. It is cost effective because Coating deposition occurs at a high cathodic current density and has a high coating deposition rate. The coatings obtained by the proposed method have high microhardness and wear resistance, which allows them to be used in the national economy for the restoration and hardening of surfaces of machine parts.

Claims (1)

The method of electrolytic deposition of a coating of molybdenum iron disulfide, comprising deposition from an electrolyte containing iron sulfate and hydrochloric acid, characterized in that an electrolyte containing additional molybdenum disulfide is used, in the following ratio of components, kg / m ³ :
iron sulfate 400-600 molybdenum disulfide 100-200 hydrochloric acid 0.5-1.5
on an asymmetric alternating current with an asymmetry coefficient β = 1.2-6.0 and a cathode density of 20-80 A / dm ² with mechanical stirring of an electrolyte with a temperature of 20-40 ° C and an acidity of pH 0.8-1.0.