RU2410473C1 - Method of electrolytic deposition of iron-titanium-cobalt alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to electrolytic deposition of hard wear-resistant coats used for reclamation and hardening of steel part surfaces. Proposed method comprises alloy deposition at AC asymmetric current that features asymmetry factor of 1.2-6 and frequency of 50 Hz from electrolyte comprising the following components, in g/l: iron chloride - 350-400, titanium oxalate - 15-25, cobalt chloride - 10-15 and hydrochloric acid - 0.5-1.5. Note here that deposition is carried out in cathode current density range of 15-40 A/dm² at electrolyte temperature of 20-40°C.

EFFECT: coat micro hardness makes 9200 MPa, friction coefficient makes 0,02.

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Description

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

A known 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 С25В 3/56, 5/18. Method of electrolytic deposition of an alloy of iron-cobalt). The resulting coatings have a low coefficient of friction, resulting in increased wear resistance of the coating, and high adhesion to the base. The disadvantage is insufficient microhardness of the coating.

A known method of electrolytic deposition of an iron-titanium alloy from an electrolyte containing 350-400 g / l of iron chloride, 15-25 g / l of oxalic titanium and 0.5-1.5 g / l of hydrochloric acid (patent No. 2230139, IPC С23В 5 / 04. Method of electrolytic deposition of an alloy of iron-titanium). 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.

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-titanium-cobalt from an electrolyte containing, g / l:

Iron chloride 350-400 Oxalic titanium 15-25 Cobalt chloride 10-15 Hydrochloric acid 0.5-1.5

The deposition process is carried out on alternating asymmetric current with a frequency of 50 Hz, starting with an asymmetry coefficient of 1.2 and increasing to 6, the cathode current density of 15-40 A / dm ² , the electrolyte temperature of 20-40 ° C. The chemical composition of the coating includes: cobalt - up to 2%, titanium - up to 3%, the rest - iron. The acidity of the electrolyte is pH 0.8-1.2. This process is cost effective, 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. Titanium provides high microhardness and adhesion to the base metal. Cobalt acts as a dry lubricant and provides a low coefficient of friction.

The electrolyte is obtained by combining aqueous solutions of ferric chloride, titanium oxalic acid and cobalt chloride.

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 (Shvetsov AN Fundamentals of the restoration of parts by ostalivanie. Omsk, 1973, p.77-79).

The amount of titanium oxalic acid is in the range of 15-25 g / l. Below 15 g / l, the use of oxalic titanium is impractical because the resulting microhardness coatings are close to hard iron coatings. Above 25 g / l, the use of oxalic titanium leads to the formation of titanium oxides, which dramatically reduces the quality of the coating and its microhardness. The most optimal is the content of titanium oxalic acid 20 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.

The temperature range is in the range of 20-40 ° C. The lower limit is limited by the diffusion properties of the electrolyte. The movement of ions 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 ² 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 starts from 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.

Based on the tests, the optimal conditions for the electrodeposition method of the iron-titanium-cobalt alloy are the conditions described in the example.

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

Iron chloride 350 Oxalic titanium twenty Cobalt chloride fifteen Hydrochloric acid 1,0

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 is gradually increased to β = 6 over 3-5 minutes. The coating has Gcc = 300 MPa, microhardness Нµ = 9200 MPa, deposition rate of 0.25 mm / h and includes: cobalt - up to 2%, titanium - up to 3%, the rest - 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)

Method of electrolytic deposition of an iron-titanium-cobalt alloy on an alternating asymmetric current with an asymmetry coefficient of 1.2-6 and a current frequency of 50 Hz from an electrolyte containing ferric chloride, oxalic titanium, hydrochloric acid, characterized in that cobalt chloride is additionally introduced into the electrolyte at the following ratio of components, g / l:
ferric chloride 350-400 oxalic titanium 15-25 cobalt chloride 10-15 hydrochloric acid 0.5-1.5
and the deposition is carried out in the range of cathodic current densities of 15-40 A / dm ² at an electrolyte temperature of 20-40 ° C.