RU2250936C1 - Method for electrolytic deposition of iron-boron alloy-based coat - Google Patents

Abstract

FIELD: electrolytic deposition of hard, wear resistant coats, in particular iron-boron coats useful in surface reducing and hardening.

SUBSTANCE: claimed method includes coat deposition from electrolyte containing (kg/m³): boric acid 2.5-60; iron (II) chloride 300-450; hydrochloric acid 0.5-1.5 and water, by using alternate asymmetric current with asymmetric coefficient of 1.2-6; cathode current density of 15-60 A/dm³, at electrolyte temperature of 20-40°C and pH 0.8. Method of present invention makes it possible to increase capability and deposition rate; to decrease electrolyte temperature; and to improve cohesive resistance between coat and support.

EFFECT: coats of increased microhardness and wear resistance.

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Description

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

A known method of electrolytic deposition from ferrous chloride electrolyte containing 200-250 kg / m ^{3 of} ferric chloride and 2-3 kg / m ^{3 of} hydrochloric acid (Melkov M.P. Solid cooling of automotive parts. M .: Transport, 1971. p.19 -20). However, this electrolyte operates at a high temperature (60-80 ° C) and provides coatings with a microhardness value of 4500-6500 MPa.

The prototype is a method for the deposition of an electrolytic coating from an electrolyte containing: ferric chloride (or sulfate, ferric) 80-120 kg / m ³ , triethanolamine 150-170 kg / m ³ , Trilon B 120-140 kg / m ³ , caustic soda 80-100 kg / m ³ , sodium borohydride 0.5-1.0 kg / m ³ . The deposition of the coating takes place at a constant current (Levinzon A.M. Electrolytic deposition of metals of the iron subgroup. - L.: Mechanical Engineering, Leningrad Department, 1983. - 96 p., Ill. - (B-galvanic engineering / Ed. P .M. Vyacheslavova; Issue 3)).

The disadvantage of this method is the limited microhardness of the coating, low adhesion of the coating to the base, low deposition rate of the coating and the use of high electrolyte temperatures.

To eliminate the above disadvantages, a method of electrolytic deposition of an iron - boron alloy is proposed, which has high productivity due to the use of an alternating asymmetric current. It is cost effective because deposition occurs at high cathodic current densities and low electrolyte temperatures, which ensures a high deposition rate of coatings. The resulting coatings have high adhesion to the base, high microhardness and wear resistance. Precipitation occurs from an electrolyte containing: boric acid, iron chloride (II), hydrochloric acid in the following ratio of components, kg / m ³ :

boric acid 2.5-60

iron chloride (II) 300-450

hydrochloric acid 0.5-1.5

Electrolysis is carried out at a temperature of 20-40 ° C with alternating asymmetric current with an interval of cathodic current densities of 15-60 A / dm ² and an asymmetry coefficient β = 1.2-6. The acidity of the electrolyte is in the range of pH 0.8.

The electrolyte is obtained by combining an aqueous solution of ferric chloride and boric acid.

Boric acid is in the range of 2.5-60 kg / m ³ . The lower limit is due to the fact that when the content is less than 2.5 kg / m ³ boric acid, there is no noticeable change in the physico-mechanical properties of the coating. The upper limit is limited to a boric acid content of 60 kg / m ³ . When the content is more than 60 kg / m ³ , intensive formation of boron oxides occurs, which sharply reduces the physicomechanical properties of the electrolytic coating: the adhesion of the coating decreases, the microhardness decreases, and the porosity and roughness of the coating increase.

The concentration of ferric chloride is in the range of 300-450 kg / m ³ . 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 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 simultaneous rarefaction of hydrogen. With an increase in the content of hydrochloric acid, the amount of rarefied 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 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 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 15-60 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. At a cathodic current density above 60 A / dm ² , strong dendritic formation occurs and the current efficiency decreases sharply.

The beginning of coating deposition occurs starting from the asymmetry coefficient β = 1.2, which provides high adhesion of the coating to the substrate, Gst = 300 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 direct current. Due to the different values of the asymmetry coefficient, it is possible to obtain coatings with various physical and mechanical properties.

Based on the tests, the optimal conditions for the method of electrodeposition of the iron - boron alloy are the conditions given in the example.

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

boric acid 50

iron chloride (II) 350

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 40 A / DM ² . The deposition process begins at β = 1.2 and is gradually increased to β = 5 over 3-5 minutes. The coating has Gst = 300 MPa, microhardness Hμ = 9000 MPa, deposition rate of 0.35 mm / h.

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 an iron-boron alloy from an electrolyte containing boric acid, ferric chloride (II), hydrochloric acid, characterized in that the deposition is from an electrolyte containing, kg / m ³ : Boric acid 2.5-60 Iron chloride (II) 300-450 Hydrochloric acid 0.5-1.5 on an alternating asymmetric current with an asymmetry coefficient of 1.2–6, at a cathodic current density of 15–60 A / dm ² , an electrolyte temperature of 20–40 ° C, and an acid pH of 0.8.