Method for forming protective oxide-ceramic coating on surface of valve metals and alloys

Abstract

FIELD: protective coatings.SUBSTANCE: method for forming a protective oxide-ceramic coating on the surface of products made of valve metals and alloys by the plasma electrolytic oxidation method involves immersing the product as an electrode together with a counter electrode in a bath filled with an aqueous alkaline electrolyte, and sequentially supplying rectangular pulses of anode and cathode voltage to the electrodes using a pulsed power source while regulating the repetition rate of the current pulses. The current densities in the anode circuit are 20.5-27 A / dm2 and in the cathode circuit 25.5-33 A / dm2, the pulse repetition frequency is from 1000 to 4000 Hz.EFFECT: improving the properties of the resulting oxide-ceramic coatings.1 cl, 8 ex

Description

[0001] The invention relates to the field of applying protective coatings, in particular to plasma-electrolytic oxidation of products made of valve metals and alloys and can be used to form oxide-ceramic coatings on the surface of products with increased wear and corrosion resistance, heat resistance, and dielectric strength.

[0002] A method is known for applying a coating to products made of a valve metal or its alloy, which includes immersing the product in a bath with an aqueous electrolyte solution and forming a coating in a pulsed anodic-cathode mode, wherein the anode voltage is varied in the range from 300 V to 600 V, the cathode voltage is kept constant from 0 V to 300 V, the pulse repetition frequency is varied in the range from 30 Hz to 1000 Hz (patent RU 2736943, published 23.11.2020. Bulletin No. 33).

[0003] The disadvantages of the known solution include a narrow voltage range of 300 V to 600 V and an insufficient frequency: up to 1000 Hz. According to the applicant, a voltage range of 85 V to 1000 V is required, with 1000 V being preferable. The frequency should be above 1000 Hz and up to 4000 Hz.

[0004] The closest in terms of the set of essential features - the prototype of the claimed invention - is a method for forming a protective oxide-ceramic coating on the surface of products made of valve metals and alloys by plasma electrolytic oxidation (hereinafter - PEO), including immersing the product as an electrode together with a counter electrode in a bath filled with an aqueous alkaline electrolyte, and sequentially supplying rectangular pulses of anodic and cathodic voltage to the electrodes using a pulsed power source (patent RU 2681028, published 01.03.2019. Bulletin No. 7). According to a known solution, the processing is carried out at effective current densities in the anode circuit of 5-20 A / dm2 and in the cathode circuit 6-25 A / dm 2 depending on the nature of the material being processed. The pulse repetition rate was 3.3–33 kHz.

[0005] Disadvantages of the known solution include, in particular, low current densities in the anodic and cathodic circuits, leading to deterioration of the properties of the resulting coating. Based on the applicant's experience, the current density in both circuits needs to be increased.

[0006] The technical objective of the proposed invention is to improve the technological process of forming an oxide-ceramic coating.

[0007] The technical result of implementing the proposed invention is the production of oxide-ceramic coatings with improved properties.

[0008] The solution to the technical problem is achieved due to the fact that in the proposed method for forming a protective oxide-ceramic coating on the surface of valve metals and alloys (hereinafter referred to as the method), which includes immersing the product as an electrode together with a counter-electrode in a bath filled with an aqueous alkaline electrolyte, and sequentially supplying rectangular pulses of anode and cathode voltage to the electrodes using a pulsed power source at current densities in the anode circuit of 20.5-27 A / dm 2 and in the cathode circuit 25.5-33 A / dm 2 depending on the nature of the material being processed and the pulse repetition frequency from 1000 Hz to 4000 Hz, and the method additionally includes regulating the current pulse repetition frequency.

[0009] The claimed combination of process parameter ranges—current densities in the anode and cathode circuits and pulse repetition rates—was achieved by the applicant during experimental work. This study investigated the formation of oxide-ceramic coatings on the surfaces of aluminum, titanium, magnesium, zirconium, tantalum, niobium, beryllium, and their alloys. Work was conducted to optimize a number of process parameters, including the ratio of the anode pulse duration to the dead time.

[0010] To compare the proposed method and the method described in the technical solution adopted as the closest analogue (hereinafter referred to as method “P”), the applicant conducted a series of experiments repeating the experiments described in the said solution.

[0011] Examples of the invention.

[0012] Disks of heat-resistant aluminum alloy AK4-1 T1 (2618 T6), 62 mm in diameter and 6.5 mm thick, were used as samples (5 each for method "P" and 20 each for the claimed method). During oxidation, the disk, along with two stainless steel counter electrodes, was placed in a bath of alkaline silicate electrolyte.

[0013] When conducting experiments using the claimed combinations of operating parameters, the applicant tested the following options:

[0014] 1) Current density in the anode circuit: 15 A / dm 2 ; current density in the cathode circuit: 21 A / dm 2 ; pulse repetition frequency 1000 Hz.

[0015] 2) Current density in the anode circuit: 15 A / dm 2 ; current density in the cathode circuit: 33 A / dm 2 ; pulse repetition frequency 1000 Hz.

[0016] 3) Current density in the anode circuit: 27 A / dm 2 ; current density in the cathode circuit: 21 A / dm 2 ; pulse repetition frequency 1000 Hz.

[0017] 4) Current density in the anode circuit: 27 A / dm 2 ; current density in the cathode circuit: 33 A / dm 2 ; pulse repetition frequency 1000 Hz.

[0018] 5) Current density in the anode circuit: 15 A / dm 2 ; current density in the cathode circuit: 21 A / dm 2 ; pulse repetition frequency 4000 Hz.

[0019] 6) Current density in the anode circuit: 15 A / dm 2 ; current density in the cathode circuit: 33 A / dm 2 ; pulse repetition frequency 4000 Hz.

[0020] 7) Current density in the anode circuit: 27 A / dm 2 ; current density in the cathode circuit: 21 A / dm 2 ; pulse repetition frequency 4000 Hz.

[0021] 8) Current density in the anode circuit: 27 A / dm 2 ; current density in the cathode circuit: 33 A / dm 2 ; pulse repetition frequency 4000 Hz.

[0022] When simulating the process with operating parameters using the “P” method, rectangular voltage pulses with a pulse repetition frequency of 5700 Hz were applied to the electrodes (method “P”, 5 samples).

[0023] After completing the coating formation process, thickness, hardness, elastic modulus, and adhesive and cohesive strength were measured on all samples. The spread of the obtained values ​​for the coatings obtained by the claimed method did not exceed the measurement error. Furthermore, no cracks, peeling, or other defects were detected in the coatings obtained by the claimed method. The measured characteristics of the coatings formed using the proposed combinations of process parameters exceed those of the coating formed by the "P" method by 2-5%.

[0024] The above allows us to state that the declared technical result has been achieved.

Claims

A method for forming a protective oxide-ceramic coating on the surface of products made of valve metals and alloys by plasma electrolytic oxidation, which includes immersing the product as an electrode together with a counter electrode in a bath filled with an aqueous alkaline electrolyte, and sequentially supplying rectangular pulses of anode and cathode voltage to the electrodes using a pulsed power source, characterized in that the current density in the anode circuit is 20.5-27.0 A / dm 2 and in the cathode circuit 25.5-33.0 A / dm 2 Depending on the nature of the material being processed, the pulse repetition frequency ranges from 1000 to 4000 Hz, and additionally includes regulation of the current pulse repetition frequency.