RU2705843C1 - Method for electrolytic deposition of iron-boron alloy - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to electrolytic deposition of hard wear-resistant coatings, particularly iron-poride coatings used for surface reconditioning and hardening. Method involves depositing coating from electrolyte containing 200–400 kg/m³ chloride of iron, 0.6–1.4 kg/m³ sodium decahydroborate, 4.0–5.0 kg/m³ citric acid, 1.0–1.5 kg/m³ hydrochloric acid. Deposition is carried out on alternating asymmetric current with current asymmetry factor 2–7 at electrolyte temperature of 20–30 °C in the interval of cathode current densities of 60–100 A/dm².

EFFECT: high microhardness and wear resistance of the iron-bearing coating.

1 cl

Description

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

A known method of electrolytic deposition of an alloy of iron-boron from an electrolyte containing iron chloride 300-450 kg / m ³ , boric acid 2.5-60 kg / m ³ , hydrochloric acid 0.5-1.5 kg / m ³ . The deposition process is conducted on an alternating asymmetric current, starting from an asymmetry coefficient of 1.2 and increasing to 6, a cathode current density of 15-60 A / dm ² , an electrolyte temperature of 20-40 ° C and an electrolyte pH of 0.8 (Patent No. 2250936, 2003)

The disadvantage of this method is the large consumption limits of the alloying element (boric acid) of 2.5-60 kg / m ³ and a low content of the alloying element in the coating of about 1.0%, which in turn does not make it possible to obtain maximum microhardness and wear resistance of the electrolytic iron-boride coating .

To eliminate the above disadvantages, a method for electrolytic deposition of an alloy of iron-boron from an electrolyte of the following composition, kg / m ³ :

Ferric chloride 200-400 Sodium Decahydroborate 0.6-1.4 Lemon acid 4-5 Hydrochloric acid 1.0-1.5

The deposition process is carried out on an alternating asymmetric current, starting with an asymmetry coefficient of 2 and increasing to 7, a cathode current density of 60-100 A / dm ² , and an electrolyte temperature of 20-30 ° C. The acidity of the electrolyte is in the range of pH 0.8-1.2.

An electrolyte of this composition is obtained by combining aqueous solutions of iron chloride, sodium decahydroborate and citric acid. Hydrochloric acid is added to maintain acidity.

The concentration of iron chloride is in the range of 200-400 kg / m ³ . The lower limit indicates the zone of minimum viscosity. The upper limit indicates the zone of maximum electrical conductivity.

The content of sodium decahydroborate is in the range of 0.6-1.4 kg / m ³ . Below 0.6 kg / m ^{3 the} use of sodium decahydroborate is impractical because the resulting hardness coating is close to hard iron coating. Above a concentration of 1.4 kg / m ^{3, the} use of sodium decahydroborate changes the physicomechanical properties of the coating; brittleness sharply increases due to the formation of boron oxides, which negatively affects the wear resistance of the coating.

The content of hydrochloric acid is in the range of 1.0-1.5 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 1.0 kg / m ³ there is a strong alkalization of the cathode layer. Hydroxide formed in the near-cathode layer is included in the coatings and this worsens their structure.

The content of citric acid is in the range of 4-5 kg / m ³ . Below 4 kg / m ^{3 the} use of citric acid is impractical because citric acid is the link between sodium decahydroborate and iron chloride. An insufficient amount of citric acid negatively affects the quality of the electrolyte, and subsequently the content of the alloying component in the electrodeposited coating. The upper limit is limited from an economic point of view, because at a concentration of more than 5 kg / m ^{3 of} citric acid, there is no change in the quality of the electrolyte and the concentration of the alloying element in the coating. Citric acid also acts as a stabilizer in the electrolyte and prevents the formation of ferric iron.

Alternating asymmetric current makes it possible to conduct the process at a low temperature of 20-30 ° C. The lower limit is limited by the diffusion properties of the electrolyte. The movement of ions is slow and the deposition rate is low. Above 30 ° C, the use of electrodeposition of coatings is unprofitable, because the resulting coatings have low microhardness.

The cathodic current density is in the range of 60-100 A / dm ² . Below 60 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 greater than 100 A / dm ² , intense dendritic formation occurs and the current efficiency sharply decreases.

The process of deposition of the coating occurs on alternating asymmetric current with an asymmetry coefficient of 2-7. The onset of deposition takes 2-3 minutes with an asymmetry coefficient β = 2. In this case, a coating of reduced hardness is formed, which has high adhesion to the base Gst = 350 MPa. Then, the anode component gradually decreases to the asymmetry coefficient β = 7, which is characterized by a stable deposition rate and a high microhardness of the coating. A further increase in β is not recommended because the process is no different from direct current deposition.

Based on the tests performed, the optimal conditions of the method are the conditions given as an example:

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

Ferric chloride 350 Sodium Decahydroborate 1,0 Lemon acid 5,0 Hydrochloric acid 1,5

The electrodeposition process is carried out at a temperature of 25 ° C and a cathodic current density of 80 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 an asymmetry coefficient of 2, which is increased to 7. Subsequently, deposition occurs at an asymmetry coefficient of 7. The coating has an adhesion of Gcc = 350 MPa and a microhardness of 9500 MPa. Coating composition: iron - 97%, boron - 3% (in the prototype about 1.0%). The electrodeposition rate is 0.5 mm / h (in the prototype 0.35 mm / h.).

The proposed method has high productivity due to the use of an asymmetric alternating current with a high cathode density and a high boron content in the electrolytic coating. It is cost effective because coating deposition occurs at a high cathodic current density and has a high coating deposition rate of up to 0.5 mm / h. The coatings obtained by the proposed method have high microhardness and wear resistance due to the high boron content in the electrolytic coating, which allows them to be used in the repair industry to restore and harden the surfaces of machine parts.

Claims (3)

The method of electrolytic deposition of an iron-boron alloy from an electrolyte containing iron chloride, a boron-containing compound and hydrochloric acid, characterized in that citric acid is additionally introduced into the electrolyte composition, sodium decahydroborate is used as a boron-containing compound in the following ratio, kg / m ³ : ferric chloride 200-400 sodium decahydroborate 0.6-1.4 hydrochloric acid 1.0-1.5 lemon acid 4.0-5.0, and the deposition is carried out on an alternating asymmetric current with a current asymmetry coefficient of 2-7 at an electrolyte temperature of 20-30 ° C in the range of cathodic current densities of 60-100 A / dm ² .