RU2543659C1 - Method for production of composite metal-ceramic coating at valve metals and their alloys - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: method for production of composite metal-ceramic coating at substrate of valve metal or its alloy, mainly at substrate made of aluminium, magnesium, titan, zirconium or their alloys, includes three stages. At the first stage formation of thin ceramic sublayer with thickness of 7-12 mcm is made at substrate. At the second stage formation of porous ceramic layer is made with required thickness, at that this layer consists mainly of oxides of the base material and additionally of copper and/or nickel oxides. At the third stage operation of copper and/or nickel recovery is made up to metal from their compounds in order to form metallic phase in porous ceramic layer obtained at the second stage.

EFFECT: production of composite metal-ceramic coating having surface conduction.

11 cl, 3 dwg, 4 ex

Description

The invention relates to the field of electrolytic coating using chemical reactions on the surface, for example, the formation of transformed layers, namely, microplasma oxidation of valve metals and can be used to obtain functional coatings, including conductive coatings in electronics and microelectronics.

WO 0112883 A1 (“ISLE COAT LTD” [GB]; SHATROV ALEXANDR SERGEEVICH [RU]) “LIGHT ALLOY-BASED COMPOSITE PROTECTIVE MULTIFUNCTION COATING” discloses a composite protective multifunctional coating containing light metals and their alloys (Al, Mg, Ti, Nb, Al-Ti, Al-Be, Ti-Nb), consisting of a ceramic layer of solid and stable oxide, which is the shape of the matrix and filling the pores of the matrix (pore diameter from several tens of nanometers to several microns) with substances having functional purpose. Functional substances are selected from the group of metals (Ni, Cu, Co, Fe, Cr, Mo, Ti, Al, Sb, Ag, Zn, Cd, Pb, Sn, Bi, Zn, Ga) and / or metal compounds (carbides, oxides , nitrides, borides, silicides of metals of groups IV-VI of the Periodic Table of the Elements) or mixtures thereof. To obtain a matrix with an open porosity of 10-20% (an ideal matrix for creating a composite coating), electrolyte-plasma oxidation was used, and then substances were introduced into the pores that improve the strength, hardness and resistance to wear and corrosion, as well as ductility and resistance to dynamic contact loads and vibration. Then carried out a machining. In the description of the example, the matrix production modes are given: phosphate-silicate electrolyte (pH 11), anode-cathode mode at a current density of 20 A / dm ² , final voltage amplitudes: anode - 600 V, cathode - 190 V. Coating thickness - 120 μm, open porosity - 20%. Subsequently, the coated sample was subjected to chemical deposition of nickel and then polished. The nickel penetration depth after polishing was 10 μm. In Example 4, electrolyte-plasma anodizing of titanium in an aluminate-sulfate electrolyte was performed. The current density was 50 A / dm ² , the voltage at the anode was 550 V, at the cathode 120 V. The open porosity was 12%. Example 5 shows the possibility of forming a matrix on a magnesium alloy. Aluminate fluoride electrolyte was used. The current density was 8 A / dm ² , the voltage at the anode was 480 V, at the cathode 110 V, the open porosity was 25%.

The use of a constant reference voltage or a reference anode-cathode voltage leads to high energy consumption, heating of the electrolyte, a small processing surface and, most importantly, to a high roughness of the part. For further use of the part, subsequent machining is necessary. And only after that they begin to precipitate nickel and subsequent polishing. Machining is a time-consuming operation, and for a number of parts of complex shape, the implementation of such processing is not possible.

Russian patent RU 2250937 C1 (Penza State University (RU)) discloses a method for producing coatings, which includes microarc oxidation of products from magnesium, aluminum, titanium, zirconium, niobium, tantalum and their alloys in alkaline or acid electrolytes with the formation of coatings based on ceramic, polymer, metal, glassy, ceramic-metal, ceramic-polymer, ceramic-glassy powder particles uniformly moving in an electrolyte solution near the coated surface of the products and have their melting temperature not exceeding the temperature microarc bits, wherein the particle size should not exceed 5 microns and the proportion - 0.5-5% by weight of the electrolyte. As powder particles in the formation of coatings used:

- ceramic (porcelain, barium titanate-based ceramic, steatite-based magnesium silicate, forsterite-based magnesium orthosilicate, zircon, fluorinated carbon);

- polymer (polyvinyl butyral, low pressure polyethylene, polyamides);

- metal (nickel, aluminum, titanium, copper);

- glassy (glass sheet technical, quartz, stable hardware, Mazda, Pyrex);

- ceramic-metal (nickel and porcelain, aluminum and carbon);

- ceramic-polymer (carbon fluoride and polyvinyl butyral, polyamides and porcelain);

- ceramic-glassy (technical glass and carbon, porcelain and fluorinated carbon).

Composite coatings obtained using electrolytes containing powders are known earlier and in this work this technique leads to the formation of a composite coating. However, the introduction of powders into the electrolytes of microplasma oxidation leads to a complication of the process. Low-temperature powders can disappear in the process of arc discharges, which leads to contamination of the electrolyte. In addition, the introduction of significant quantities of material from the powders into the coating composition requires a lengthy process. The patents give the results of short-term use of the developed electrolytes, as a rule, the resource of such electrolytes is small.

In US patent US 6875334 B (publ. 05.04.2005) discloses a method and composition for introducing Nickel into the coating composition in its individual sections to obtain an electrically conductive coating, especially on magnesium. First, anodization is carried out, while it is carried out under conditions that either exclude sparking, or when sparking in an aqueous solution including hydroxylamine, phosphate anions, nonionic surfactants and alkali metal hydroxides, and then carry out the electrochemical process in the second composition of the electrolyte, which is an aqueous solution, including divalent nickel.

Chemical nickel plating, performed after obtaining a ceramic matrix, does not provide a sufficient depth of penetration of the metal and its reliable adhesion to the matrix.

The objective of the invention is to develop a technology that allows the formation of composite functional metal-ceramic inorganic layers with surface conductivity using the method of microplasma oxidation (microarc treatment in electrolyte solutions).

The problem is achieved in that the proposed method for producing a composite cermet coating on valve metals and their alloys, mainly on a substrate made of aluminum, magnesium, titanium, zirconium and their alloys, includes the following steps:

- at the first stage, the formation on the substrate of a thin ceramic sublayer with a thickness of 7 to 12 μm, mainly by microplasma oxidation in an aqueous electrolyte solution;

- at the second stage, the subsequent formation on the sublayer formed at the first stage of the porous ceramic coating of the required thickness containing copper and / or nickel compounds by microplasma oxidation in an aqueous electrolyte solution;

- and, additionally, in the third stage, the operation of reducing copper and / or nickel to metal from their compounds to form in the porous ceramic coating obtained in the second stage, the metal phase.

In addition, at the first stage, to obtain a thin ceramic sublayer, the substrate is placed in the first electrolyte solution as one of the electrodes — the anode and between the anode and cathode, also placed in the electrolyte solution, and voltage pulses are applied that have a substantially trapezoidal shape with amplitude 100-1000 V and a duration of 50-500 μs, preferably 200-600 μs and, most preferably, 300-450 μs.

Preferably, the first solution is an aqueous solution containing from 10 to 40 g / l of water-soluble phosphates and / or hydrophosphates and / or phosphoric acid and / or from 2 to 20 g / l of water-soluble fluorides and / or from 10 to 20 g / l of alkali metal tetraborates and / or boric acid and / or 10 to 60 g / l of water-soluble metasilicates and / or 1 to 20 g / l of soluble alkali metal hydroxides.

In addition, at the second stage, the substrate is placed, containing a thin ceramic layer formed in the first electrolyte solution, as one of the electrodes — the anode in the second electrolyte solution, and voltage pulses having a substantially trapezoidal shape with an amplitude of up to 500 are applied In and with a duration of 50-300 μs between the treated substrate and the cathode placed in the same solution.

Preferably, the second solution for forming a porous ceramic coating, consisting mainly of oxides of the base material and optionally oxides of copper and / or nickel, is similar to the first solution and further comprises water-soluble compounds of copper and / or nickel.

In addition, the concentration of water-soluble compounds of copper and / or nickel in the second electrolyte solution is from 2 to 50 g / l.

Preferably, copper or nickel in said compound is present as a complex anion.

In addition, copper and / or nickel compounds are used in which the metal to be introduced is present as a complex anion.

Moreover, said copper compound is selected from the group of compounds consisting of potassium tetracyano cuprate (K ₃ [Cu (CH) ₄ ]), sodium tetracyano cuprate (Na ₃ [Cu (CN) ₄ ]), copper pyrophosphate (Cu ₂ P ₂ O ₇ ) .

Moreover, to obtain a copper compound, including a complex copper-containing anion, copper pyrophosphate is previously dissolved in a solution of potassium pyrophosphate.

In addition, a complex copper or nickel-containing anion can be obtained by mixing an aqueous solution of a copper or nickel salt and a complexing agent.

Potassium hexacyanonicelate (K ₄ [Ni ₂ (CN) ₆ ]) is used as the nickel compound mentioned.

To form a metal phase in the third stage in the pores of the ceramic coating of copper and / or nickel compounds, they are reduced.

The recovery is carried out either by placing the substrate in a chamber containing a pair of reducing agent, or by purging with a gaseous reducing agent.

At the first stage, the surface of the processed substrate is cleaned and a ceramic layer is formed, consisting mainly of oxides of the substrate material.

The duration of the first stage is determined by the type of base material and the composition of the electrolyte used.

The process at the second stage is carried out until the required coating thickness is achieved under conditions of the existence of microplasma discharges in the place of contact of the treated substrate with the electrolyte solution.

During the second stage, a layer is formed consisting of oxides of the base material and other oxygen-containing compounds of the base elements and the components of the solution for microplasma oxidation and oxides of introduced metals (copper and / or nickel). The sublayer obtained in the first stage grows, and copper and / or nickel oxides precipitate with it.

In a third step, the reducing agent is selected from the group consisting of carbon monoxide, hydrogen, methanol, ethanol, natural gas, ammonia, or a mixture thereof.

The affinity of copper / nickel to oxygen is quite small, therefore, these elements are easily reduced from oxides to a metallic state:

CuO + CO → Cu + CO ₂ .

NiO + H ₂ → Ni + H ₂ O.

In this case, the oxides of the base material are not reduced. As a result, a composite cermet material is formed in which the metal phase is dispersed in the ceramic matrix over the entire pore depth and has tight adhesion with it.

To increase the continuity of the metal phase and increase the electrical conductivity of the coating, an operation of applying a copper coating by any of the known methods can be additionally carried out.

Moreover, the already introduced metal will play the role of crystallization and autocatalysis centers, which will significantly increase the speed of the process. In this case, the additionally introduced metal will fill the cermet matrix throughout the entire pore depth.

The use of copper as a modifier of a ceramic surface is most preferable based on its high electrical conductivity.

The invention is further illustrated by graphic materials and examples of its specific implementation.

Figure 1 presents a micrograph of the surface of a sample of a substrate made of an aluminum alloy D16 coated with a cermet coating after additional electrochemical nickel plating.

Figure 2 presents a photomicrograph of the surface of a sample of a substrate made of VT1-0 titanium alloy with a deposited ceramic sublayer (after the first processing step).

Figure 3 presents a micrograph of the surface of a sample of a substrate made of a VT1-0 titanium alloy coated with a ceramic coating (after the third processing step).

Example 1

A sample (in the form of a tablet with a diameter of 30 mm and a thickness of 4 mm) made of an aluminum alloy D16 was placed in a 5% solution of sodium carbonate at a temperature of 60 ° C for 2 minutes. Then the sample was clarified in concentrated nitric acid by dipping. After washing in distilled water, the sample was transferred to a bath with an electrolyte solution for microplasma oxidation: an aqueous solution containing 40 g / l sodium hydrogen phosphate and 20 g / l potassium fluoride, the rest was distilled water.

The sample was connected to the positive pole of the power source; the cathode connected to the negative pole of the power source was a bath made of stainless steel.

The sample was processed by passing the pulse current of the following parameters: pulse voltage amplitude - 400 V, pulse duration - 300 μs, pause between the anode and cathode component of the pulse - 600 μs, processing time - 10 minutes.

As a result, a ceramic layer about 10 μm thick was formed on the surface of the sample, consisting predominantly of γ-Al ₂ O ₃ .

At the second stage, copper pyrophosphate was added to the solution for microplasma oxidation at the rate of 15 grams per liter of solution at a solution pH of 8–9. Before adding copper pyrophosphate to the sample, a concentrated potassium pyrophosphate solution was poured into the solution until the precipitate was completely dissolved.

The connection scheme to the power source was the same as in the first stage. The sample was processed by passing the pulse current of the following parameters: pulse voltage amplitude - 300 V, pulse duration 100 μs, pause between the anode and cathode component of the pulse - 600 μs, processing time - 25 minutes. Then the sample was removed from the solution, washed with distilled water and dried.

As a result, a ceramic layer with a thickness of about 25 μm was formed on the surface of the sample, consisting mainly of γ-Al ₂ O ₃ with inclusions of copper (II) oxide.

In the third stage, the part was placed in a chamber and under a pressure of 300 kPa at a temperature of 120 ° C was purged with carbon monoxide for 15 minutes.

As a result, a composite metal oxide layer was formed on the surface of the sample, in which the metallic phase of copper is dispersed in a ceramic matrix, which consists mainly of amorphous alumina, and has tight adhesion with it.

To increase the continuity of the coating and the microhardness of the conductive layer, electrochemical nickel plating was carried out at the next stage. For this, an electrolyte of the composition was used: 200 g / l of nickel heptahydrate, 10 g / l of sodium chloride, 30 g / l of boric acid. The current density was 2 A / dm ² . The sample served as a cathode. The microhardness of the surface nickel layer was 2 GPa with a transition (contact) electrical resistance of 5.6 mOhm. A micrograph of the surface is shown in FIG.

Example 2

A sample with the dimensions as in Example 1, made of VT1-0 titanium alloy, was placed in a 5% solution of ammonium bifluoride at a temperature of 25 ° C for 2 minutes. After washing in distilled water, the sample was transferred to a bath with an electrolyte solution for microplasma oxidation and connected to a power source, as described in example 1. A solution for microplasma oxidation — sodium hydrogen phosphate Na ₂ HPO ₄ —30 g / l; sodium fluoride NaF - 2 g / l, boric acid H ₃ BO ₃ - 10 g / l, the rest is distilled water. The sample was processed by passing a pulse current with parameters, as in example 1. The processing time at the first stage was 0.5 minutes.

As a result, a porous ceramic layer with a thickness of about 12 μm, consisting mainly of anatase, was formed on the surface of the sample (Fig. 2).

At the second stage, copper acetate Cu (CH ₃ COO) ₂ at the rate of 50 g / L and ethylenediaminetetraacetic acid disodium salt at the rate of 40 g / L were added to the solution for microplasma oxidation.

The connection scheme to the power source was the same as in the first stage. The sample was processed by passing a pulse current with the same parameters as in the first stage. Then the sample was removed from the solution, washed with distilled water and dried.

As a result, a ceramic layer about 50 μm thick was formed on the surface of the sample, consisting of anatase with copper (II) oxide inclusions.

The process of reducing copper in a ceramic material to a metallic state was carried out as described in example 1.

As a result, a composite metal oxide layer was formed on the surface of the titanium sample, in which the metallic phase of copper was dispersed in a ceramic matrix (on the surface and in the pores), consisting mainly of anatase (Fig. 3). Transient electrical resistance of the sample was 12 mOhm.

Example 3

A sample with dimensions as in Example 1, made of an alloy of zirconium E110, was prepared as described in Example 2. An aqueous solution containing 60 g / L Na ₂ SiO ₃ · 9H ₂ O, 1 g / L hydroxide was used as a solution for microplasma oxidation. potassium. The sample was connected to the positive pole of the power source; the cathode connected to the negative pole of the power source was a bath made of stainless steel. The sample was processed by passing the pulse current of the following parameters: pulse voltage amplitude - 600 V, pulse duration - 400 μs, pause between the anode and cathode component of the pulse - 600 μs, processing time at the first stage - 0.5 minutes.

As a result, a ceramic layer about 12 μm thick was formed on the surface of the sample, consisting mainly of zirconium and zircon oxides.

At the second stage, potassium hexacyanone nickelate was added to the solution for microplasma oxidation at the rate of 10 g / L.

At the second stage, the sample was processed by passing the pulse current of the following parameters: pulse voltage amplitude - 400 V, pulse duration - 200 μs, pause between the anode and cathode component of the pulse - 600 μs, processing time - 15 minutes.

As a result, a ceramic layer was formed on the surface of the sample, consisting mainly of zirconium and zircon oxides with inclusions of nickel oxide.

At the third stage, the process of reducing nickel in a ceramic material to a metallic state was carried out by treatment with hydrogen at a temperature of 400 ° C.

To increase the continuity of the metal layer, chemical nickel plating was additionally carried out in a solution based on nickel chloride and sodium hypophosphite.

As a result, a composite metal oxide layer was formed on the surface of the zirconium sample, in which the metallic phase of nickel was dispersed in a ceramic matrix consisting mainly of zirconium and zircon oxides. The transient electrical resistance of the sample was 8.6 mOhm.

Example 4

A sample made of MA2-1 magnesium alloy was placed in a solution of sodium phosphate and sodium fluoride at a temperature of 50 ° C for 10 minutes. After washing in distilled water, the sample was transferred to a bath with a solution for microplasma oxidation and connected to a power source, as described in example 1. The solution for microplasma oxidation was an aqueous solution containing 4 g / l potassium hydroxide, 20 g / l sodium tetraborate Na ₂ B ₄ O ₇ and 12 g / l potassium fluoride, the rest is distilled water.

The sample was processed by passing the pulse current of the following parameters: the voltage amplitude of the pulses was 300 V, the pulse duration was 500 μs, the pause between the anode and cathode component of the pulse was as in example 1, the processing time was 2 minutes.

As a result, a ceramic layer about 8 μm thick was formed on the surface of the sample, consisting mainly of magnesium oxides and fluorides.

At the second stage, sodium tetracyano cuprate (Na ₃ [Cu (CH) ₄ ]) was added to the solution for microplasma oxidation with a solution pH of 11–12 at a rate of 20 grams per liter of solution.

The connection scheme to the power source was the same as in the first stage. The sample was processed by passing the pulse current of the following parameters: pulse voltage amplitude — 300 V, pulse duration — 100 μs, pause between the anode and cathode component of the pulse — as in Example 1, processing time — 10 minutes. Then the sample was removed from the solution, washed with distilled water and dried.

As a result, a ceramic layer about 20 μm thick was formed on the surface of the sample, consisting mainly of magnesium oxides and fluorides with inclusions of copper oxide.

In the third stage, the part was placed in a chamber and purged with ethanol vapor at a temperature of 80-100 ° C for 15 minutes.

As a result, a composite metal oxide layer was formed on the surface of the magnesium sample. To increase the continuity of the conductive layer, at the next stage, additional electrochemical copper plating was carried out in a cyanide electrolyte at a current density of 1 A / dm ² . The transient electrical resistance of the surface layer of the obtained composite material was 1.2 mOhm.

Claims (11)

1. A method of obtaining a composite cermet coating on a substrate of valve metal or its alloy, mainly on a substrate made of aluminum, magnesium, titanium, zirconium or their alloys, comprising the steps of forming a thin ceramic sublayer on a substrate of thickness 7 or more up to 12 microns, at the second stage, the porous ceramic layer of the required thickness is formed on the obtained sublayer, consisting mainly of oxides of the base material and additionally of and and / or nickel, and optionally in a third step performing a recovery operation copper and / or nickel to metal from their compounds to form a porous ceramic layer obtained in the second step, the metal phase. 2. The method according to claim 1, characterized in that the formation of the coating in the first and second stages is carried out mainly in the conditions of microplasma oxidation in an aqueous electrolyte solution. 3. The method according to claim 2, characterized in that in the first step, to obtain a thin ceramic sublayer, the substrate is placed as one of the electrodes — the anode in the first electrolyte solution, and voltage pulses are applied between the anode and cathode placed in the electrolyte solution, having trapezoidal shape with an amplitude of from 100 to 1000 V and a duration of from 50 to 500 μs, preferably a duration of 200-600 μs and most preferably 300-450 μs. 4. The method according to claim 3, characterized in that the first solution is an aqueous solution containing from 10 to 40 g / l of water-soluble phosphates and / or hydrophosphates and / or phosphoric acid, and / or from 2 to 20 g / l water-soluble fluorides, and / or from 10 to 20 g / l of alkali metal tetraborates, and / or boric acid, and / or from 10 to 60 g / l of water-soluble metasilicates, and / or from 1 to 20 g / l of soluble alkali metal hydroxides . 5. The method according to claim 1, characterized in that in the second stage, the substrate is placed, containing a thin ceramic sublayer formed in the first electrolyte solution, as one of the electrodes — the anode in the second electrolyte solution, and voltage pulses having a trapezoidal shape are applied , with an amplitude of up to 500 V and a duration of 50 to 300 μs between the treated substrate and the cathode placed in the same solution. 6. The method according to claim 5, characterized in that the second electrolyte solution for forming a porous ceramic coating, consisting mainly of oxides of the base material and additionally of copper and / or nickel oxides, is obtained by adding water-soluble compounds of copper and / or nickel to the first solution. 7. The method according to claim 6, characterized in that the concentration of water-soluble compounds of copper and / or nickel in the second electrolyte solution is from 2 to 50 g / l. 8. The method according to claim 6, characterized in that the introduced copper and / or nickel in said compound are contained in the form of a complex anion. 9. The method according to claim 8, characterized in that the copper and / or nickel compounds in which the metal to be introduced is contained as a complex anion are selected from the group of compounds consisting of potassium tetracyano cuprate, sodium tetracyano cuprate, copper pyrophosphate and potassium hexacyanonickelate. 10. The method according to claim 1, characterized in that the reduction of copper and / or nickel to metal from their compounds is carried out by placing a substrate in a chamber containing pairs of reducing agent, or by blowing a porous ceramic layer with pairs of reducing agent. 11. The method of claim 10, wherein the reducing agent is selected from the group consisting of carbon monoxide, hydrogen, methanol, ethanol, natural gas, ammonia, or a mixture thereof.

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