RU2401328C1 - Method of electrolytic depostion of iron-vanadium-cobalt alloy - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: deposition is carried out at AC asymmetric current with asymmetry coefficient of 1.2Ç6 and current frequency of 50 Hz from electrolyte containing the following components in wt %: iron chloride 300Ç400, sodium vanadate 5Ç8, citric acid 7Ç12, cobalt chloride 10Ç15, sulphuric acid 1.5Ç2.0 at electrolyte temperature of 20Ç40C and interval of cathode current densities of 15Ç40 A/dm2. ^ EFFECT: micro hardness of deposited coat makes 9200 MPa, friction coefficient makes 0,03. ^ 1 tbl

Description

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

A known method of electrolytic deposition of an alloy of iron-vanadium from an electrolyte containing: iron (II) chloride 350 ... 400 g / l, ammonium metavanadate 5 ... 30 g / l, hydrochloric acid 1.5 ... 2 g / l. The deposition process is conducted on an alternating asymmetric current with a frequency of 50 Hz, starting from an asymmetry coefficient of 1.2 and increasing to 6, a cathode current density of 30 ... 60 A / dm ² , an electrolyte temperature of 30 ... 50 ° C. The acidity of the electrolyte is pH 0.8 ... 1.2 (patent No. 2231578, IPC C25D / 18, 3/56 Electrolytic deposition method of an alloy of iron-vanadium. Auth. Serebrovsky V.I. and others). This deposition method provides high microhardness and adhesion to the base. The disadvantage of this method is the high coefficient of friction, which reduces wear resistance.

Also known is a method of electrolytic deposition of an alloy of iron-cobalt from an electrolyte containing: 350 ... 400 g / l of iron chloride, 5 ... 50 g / l of cobalt chloride and 0.5 ... 2.0 g / l of hydrochloric acid (patent No. 2230836, IPC C25D 3/56, 5/18 Method for electrolytic deposition of an iron-cobalt alloy). The resulting precipitation has a high adhesion to the base and a low coefficient of friction, which increases the wear resistance of the coating. However, the microhardness of the coating remains not high enough.

To obtain a coating with high adhesion to the base, high microhardness and low coefficient of friction, a method for electrolytic deposition of an alloy of iron-vanadium-cobalt from an electrolyte containing, g / l:

Iron chloride 300 ... 400

Sodium vanadate 5 ... 8

Citric acid 7 ... 12

Cobalt chloride 10 ... 15

Hydrochloric acid 1.5 ... 2

The deposition process is conducted on an alternating asymmetric current with a frequency of 50 Hz, starting with an asymmetry coefficient of 1.2 and increasing to 6, with a cathodic current density of 15 ... 40 A / dm ² , an electrolyte temperature of 20 ... 40 ° C. The chemical composition of the coating includes: cobalt - up to 2%, vanadium - up to 1.8%, the rest is iron. The acidity of the electrolyte is pH 0.8 ... 1.2. Its cost-effectiveness is obvious, because deposition occurs at high cathodic current densities and low electrolyte temperatures, which ensures a high deposition rate of coatings. Iron gives the greatest current efficiency and plays the role of a matrix. Vanadium provides an increase in the microhardness of the coating. Cobalt provides a reduction in the coefficient of friction.

The electrolyte is obtained by combining ferric chloride, sodium vanadate, citric acid, cobalt chloride and hydrochloric acid.

The concentration of ferric chloride is in the range of 350 ... 400 g / l. The lower limit indicates the zone of minimum viscosity. The upper limit shows the zone of maximum electrical conductivity (A. Shvetsov. Fundamentals of the restoration of parts by ostalivating. - Omsk, 1973, p.

Since electrolytes with sodium salts allow the use of higher current densities compared to ammonium salts, it is proposed to use sodium vanadate. The amount of sodium vanadate is in the range of 5 ... 8 g / l. Below 5 g / l, the use of sodium vanadate is impractical because the resulting microhardness coating is close to hard iron coating. Above 8 g / l, the use of sodium vanadate leads to the formation of vanadium oxides, which sharply worsens the quality of the coating and reduces the hardness of the coating. The most optimal is the content of sodium vanadate 6 ... 7 g / l.

The cobalt chloride content is in the range of 10 ... 15 g / l. Below 10 g / l, the use of cobalt chloride is impractical because the resulting coating is physically-mechanical close to the hard iron coating. Above a concentration of 15 g / l, the use of cobalt chloride leads to a deterioration in the physicomechanical properties of the coating; brittleness sharply increases, which negatively affects the wear resistance of the coating.

The content of hydrochloric acid is in the range of 0.5 ... 1.5 g / l. 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 g / l, a strong alkalization of the cathode layer occurs. Hydroxide formed in the near-cathode layer is included in the coatings and this worsens their structure.

Citric acid is necessary to create a vanadate-citrate complex. In the absence of citric acid, vanadium salts precipitate during the preparation of the electrolyte. The content of citric acid is in the range of 7 ... 12 g / l. At a concentration of citric acid below 7 g / l, the formation of a vanadate-citrate complex is difficult. Increasing the concentration of citric acid over 12 g / l does not have a noticeable effect on the quality of the coating.

The temperature range is within 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 unprofitable 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 15 ... 40 A / dm ² . Below 15 A / dm, the current density is impractical to use, because The electrolysis process has a low coating deposition rate. When the cathodic current density is above 40 A / dm ² , strong dendritic formation occurs and the current efficiency sharply decreases.

The beginning of coating deposition occurs, starting with the asymmetry coefficient β = 1, 2, which provides a high adhesion of the coating to the base Gst = 300 MPa. If the asymmetry coefficient is lower than 1, 2, the deposition process 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 direct current. Due to the different values of the asymmetry coefficient, it is possible to obtain coatings with various physical and mechanical properties.

Physico-mechanical properties of coatings depending on the asymmetry coefficient

Indicators Fe Fe-v Fe-Co Fe-v-co Microhardness, MPa 4500 ... 6300 7000 ... 8200 6800 ... 8200 8100 ... 9200 Coefficient of friction, µ 0.2 ... 0.1 0.1 ... 0.09 0.06 ... 0.04 0.03 ... 0.02

Based on the tests, the optimal conditions for the method of electrodeposition of an alloy of iron-vanadium-cobalt are the conditions given in the example:

The electrolyte consists of the following components in quantity, g / l:

Chloride Iron 350

Sodium Vanadate 6

Citric Acid 10

Cobalt chloride 12

Hydrochloric acid 1.5

The process of electrolytic deposition of the coating is carried out at a temperature of 30 ° C and a cathodic current density of 30 A / DM ² . Mild steel is the anode. Previously, the part is subjected to degreasing with Viennese lime and anode treatment in a solution of 30% sulfuric acid. The deposition process begins at β = 1, 2 and gradually over the course of 3 ... 5 minutes increase to β = 6. The coating has Gst = 300 MPa, microhardness Нµ = 9200 MPa, deposition rate of 0.25 mm / h and includes: cobalt - up to 2%, vanadium - up to 1.8%, the rest is iron.

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 and a low coefficient of friction, which allows them to be used in the national economy for the restoration and hardening of the surfaces of steel parts of machines.

Claims (1)

The method of electrolytic deposition of an alloy of iron-vanadium-cobalt from an electrolyte containing iron chloride, cobalt chloride, hydrochloric acid, characterized in that sodium vanadate and citric acid are additionally introduced into the electrolyte, the deposition is carried out from the electrolyte in the following ratio of components, g / l:
ferric chloride 300 ... 400 sodium vanadate 5 ... 8 cobalt chloride 10 ... 15 lemon acid 7 ... 12 hydrochloric acid 1,5 ... 2,0
and the deposition is carried out from the electrolyte at an alternating asymmetric current with a current asymmetry coefficient of 1.2 ... 6 and a current frequency of 50 Hz at an electrolyte temperature of 20 ... 40 ° C and a range of cathodic current densities of 15 ... 40 A / dm ² .