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 duration of the anode pulses ranges from 31 to 49 mcs, the pulse repetition frequency from 1000 to 4000 Hz.EFFECT: obtaining oxide-ceramic coatings with specified properties under reduced energy conditions.1 cl, 3 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 microarc production of a composite coating on aluminum and its alloys in a pulsed anodic-cathode mode with a duration of anodic pulse packets of 50 ms, cathodic pulses of 40 ms, and pauses between them of 10 ms (patent RU 2466218, published 10.11.2012. Bulletin No. 31).

[0003] A disadvantage of the known solution is its limited applicability to aluminum and aluminum alloys. This is due to the rigidly defined value of such an important process parameter as the duration of the anode pulse trains. According to the applicant, different materials require correspondingly different values ​​of this parameter.

[0004] The closest prototype of the claimed invention in terms of the set of essential features 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 referred to as PEO), which includes immersing the product as an electrode together with a counter electrode in a bath filled with an aqueous alkaline electrolyte, and sequentially applying 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 the known solution, the duration of the anodic pulse is 3-30 μs, depending on the nature of the materials being processed.

[0005] The disadvantages of the known solution include, in particular, the unsatisfactory density of the ceramic coating under the specified operating parameters. According to the applicant's experience, the pulse duration is related to the oxide film thickness of the workpieces. It has been established that the pulse duration required to achieve high ceramic coating density under the specified operating conditions is achieved with longer anodic pulse durations.

[0006] The technical objective of the proposed invention is to simplify 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 specified properties under reduced energy conditions (at lower values ​​of cathode voltage).

[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 pulse power source with anode pulse duration from 31 μs to 49 μs and a pulse repetition frequency from 1000 Hz to 4000 Hz, wherein the process additionally includes regulation of the current pulse repetition frequency.

[0009] The claimed range of anode voltage pulse durations was achieved by the applicant during experimental work. This work investigated the formation of oxide-ceramic coatings on the surfaces of aluminum, titanium, magnesium, zirconium, and their alloys. Work was conducted to optimize a number of process parameters, including the ratio of anode pulse duration to 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] In the first series of experiments, rectangular voltage pulses with a pulse repetition rate of 5700 Hz were applied to the electrodes (method "P," 5 samples). The anode pulse duration was 15 μs.

[0014] In the second series of experiments, rectangular voltage pulses with a duration of 31 μs and a pulse repetition frequency of 1000 Hz (the lower limit of the range of the claimed method, 5 samples) and 4000 Hz (the upper limit of the range of the claimed method, 5 samples) were applied to the electrodes.

[0015] In the third series of experiments, rectangular voltage pulses with a duration of 49 μs and a pulse repetition frequency of 1000 Hz (the lower limit of the range of the claimed method, 5 samples) and 4000 Hz (the upper limit of the range of the claimed method, 5 samples) were applied to the electrodes.

[0016] After completing the coating formation process, thickness, hardness, elastic modulus, and adhesive and cohesive strength were tested on all samples. The spread of the obtained values ​​for the coatings produced by the claimed method did not exceed the measurement error. Furthermore, the number of defects detected in the coatings produced by the claimed method was minimal (below the permissible limit). The measured characteristic values ​​corresponded to the specified values.

[0017] 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 articles made of valve metals and alloys by means of plasma electrolytic oxidation, which includes immersing the article 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 duration of the anode pulses is from 31 to 49 μs, the pulse repetition frequency is from 1000 to 4000 Hz, and additionally includes regulation of the current pulse repetition frequency.