RU2713763C1 - Method of producing a porous composite coating - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to electroplating and can be used in machine building in order to improve functional characteristics of mechanisms operating in aggressive media, as well as in oil refining products. Method includes micro-arc oxidation (MAO) of metal surface and subsequent cathodic electrodeposition of nickel with formation of solid coating, wherein MAO is carried out in silicate-phosphate-alkaline electrolyte with density of anode direct current of 5–15 A/dm² in the voltage range of 300–700 V for 15–60 minutes with formation of ceramic oxide coating in thickness range of 20–60 mcm with open porosity of not more than 15 % with average pore diameter of 15–25 mcm, having mainly round shape and uniformly distributed on surface, and nickel cathode electrodeposition is carried out inside pores of oxide film in water-based electrolyte for 40–60 minutes.

EFFECT: high microhardness, corrosion resistance of coatings and their thickness.

3 cl, 1 ex

Description

The invention relates to the field of creating non-porous composite coatings based on oxide compositions of titanium, aluminum and metallic nickel, can be used in mechanical engineering with the aim of improving the functional characteristics of mechanisms operating in aggressive environments, as well as in products of the oil refining industry.

The method includes microarc oxidation (MAO) of products made of aluminum, titanium, and their alloys in silicate-phosphate-alkaline electrolytes and subsequent cathodic deposition of metallic nickel, to form a continuous coating with enhanced protective characteristics.

In most cases, the filling of the matrix porous ceramic coating formed by the method of microarc oxidation (MAO) is carried out with polymeric materials. Thus, a known method for producing composite coatings on valve metal alloys RU 2527110 C1 C25D 11/18. According to the method, supermolecular polyethylene is deposited in the pores of the coating by universal methods, such as microplasma spraying, fusion with a burner, slip. The disadvantages of the invention include the fact that:

- with microplasma spraying, thin films are formed that cover only the surface of the pore, not filling it completely;

- when using slip and fusion, an uneven, “island” distribution of the polymer over the coating surface is observed;

- the polymer does not increase the hardness and, accordingly, the strength characteristics of the composite coating.

A known method of deposition of metals in the pores of the anodic oxide on the surface of aluminum for the manufacture of a display, Japanese patent No. 2003-257344, 09/12/2003. Display, and manufacturing method therefor. In the known method, porous alumina is formed on a layer of aluminum sprayed onto a substrate by the method of anodic oxidation, then nickel is subsequently embedded in the pores of the oxide, then gold. The proposed method of forming a composite layer has several disadvantages:

- high complexity, since the formation of layered multicomponent structures requires the creation of a complex configuration of the porous oxide layer;

- in terms of strength characteristics, the ceramic oxide coating obtained by the MAO method significantly exceeds anodized aluminum;

- this method is not universal and does not allow coating non-aluminum products.

A known electrolytic method for applying protective and insulating coatings RU 2367727 C1 C25D 11/02 with low porosity, in which the result is achieved by conducting MAO under pressure, which leads to low porosity of the formed coating. However, this method does not exclude the presence of through pores to the metal and is time-consuming due to the use of an autoclave. In addition, the thickness of the formed coating does not exceed 25 microns. This method is not universal and does not allow coating non-titanium materials.

A known method of producing nanocomposite coatings RU 2471021 C25D 15/00 C25D 11/20, taken as a prototype. The method includes microarc oxidation of the surface of titanium alloy products in an alkaline electrolyte with solid-phase ingredients in the form of powders, using titanium oxide nanopowders with a size of less than 0.05 microns, and the final coating is formed by cathodic treatment in an acid electrolyte at a temperature of 450 ° C by planting a metal phase inside the pores of the oxide coating.

The disadvantage of this method is the impact on the sample of an aggressive acidic electrolyte at a temperature of 450 ° C, which can lead to cracks in the oxide layer and pitting corrosion. The effect of open coating porosity and pore geometry on the efficiency of uniform metal deposition into coating pores is not taken into account. Also, this method is not universal and does not allow coating non-titanium materials.

The technical result of the invention is the creation of a universal non-toxic method of obtaining a porous metal-oxide-nickel ceramic-metal coating on products from aluminum, titanium and their alloys, which will lead to an increase in the functional properties of the products: corrosion resistance, surface microhardness due to a significant reduction in porosity, as well as to increase the thickness of the coating.

The technical result is achieved due to the fact that microarc oxidation (MAO) in silicate-phosphate-alkaline electrolytes when setting the anode direct current with a density of 5-15 A / dm ² in the voltage range of 300-700 V on the surface of aluminum, titanium and their alloys, the duration of the process is 15-60 minutes, a ceramic oxide coating is formed in a thickness range of 20-60 microns with an open porosity of not more than 15% with an average pore diameter of 15-25 microns, having a predominantly rounded shape and uniformly distributed over the surface. Then, the metallic phase of nickel is planted inside the pores of the oxide film by cathodic treatment in a water-based electrolyte [1] for 40-60 minutes. The electrolyte has the following composition:

- Nickel sulfate 35.0-55.0 g / l;

- sodium acetate 25.0-30.0 g / l;

- acetic acid 4.5-5.0 ml / l;

- sodium lauryl sulfate 0.1-1.0 g / l.

When setting the anode direct current with a density of more than 15 A / dm ^{2, the} formed coatings are prone to cracking around the pores, since the power of the arc discharges becomes critical. The presence of a defective structure leads to the formation of internal pores of complex geometry, which combine with open pores. This fact leads to an uneven deposition of metallic nickel in the formed pores. When setting the anode direct current with a density of less than 5 A / dm ² , the surface of the ceramic layer is loosened, which leads to a significant deterioration in the strength and adhesive properties of the matrix oxide coating. The duration of the MAO process of 15-60 minutes leads to the formation of an oxide layer with a thickness of 20-60 microns. With a further increase in the duration of the MAO process, an increase in the coating thickness and a change in the geometry of open pores occur, which complicates the process of electrochemical nickel plating and leads to an uneven growth of the metal layer.

Maintaining the voltage in the electrolytic bath in the range of 300-700 V is necessary to ensure the flow conditions of the MAO process, passing from the anodizing.

When replacing a direct current with a pulse, the open porosity of the coating decreases to 5-10%. However, the majority of pores in this case are not through, which leads to the formation of a porous cermet coating during electrodeposition by nickel.

When setting the anode direct current with a density of 5-15 A / dm ² (depending on the metal being oxidized), the surface of the oxide coating has open pores with an average diameter of 15-25 microns of rounded shape and actually consists of vertices (the largest oxide thickness) and depressions (through pore to metal, lack of a protective coating), where pitting corrosion can begin. The open porosity of the formed coating does not exceed 15%. Open pores are evenly distributed over the entire area of the formed coating. These conditions are optimal for uniform filling of open through pores with nickel during electrochemical deposition in a water-based electrolyte for 60 minutes, while the functional characteristics of the synthesized coatings increase. First of all, a metal coating is formed at the bottom of the pores, filling them and leveling the overall relief. Thus, the coating becomes non-porous, the adhesion of the metal coating increases due to the larger contact area and structural features of the porous oxide layer. When nickel is deposited for more than 60 minutes, the pores are filled and the continuous metal layer grows to a thickness of more than 5 microns, which will require an additional operation of grinding the coating. When nickel is deposited for less than 40 minutes, single through pores to the metal base are observed on the surface of the coating, which affects the functional characteristics of the coating.

The electrolyte composition is optimal for electrodeposition of a non-porous layer of metallic nickel on titanium, aluminum, and their alloys, at room temperature [1].

The technical and economic advantage of the invention compared to the prototype is expressed in the fact that the proposed method can be implemented in production with significantly lower material costs, because eliminates the need for the use of an acid electrolyte heated to 450 ° C, which in turn will reduce the cost of treatment facilities, and is also universal.

Example

A non-porous cermet coating was applied to plates of size 50 × 10 × 2 mm from A5 aluminum and VT1-0 titanium using the following technology:

1. Sample surface preparation:

2. The formation of the oxide layer on the surface of metal plates in silicate-phosphate-alkaline electrolytes.

3. The application of a nickel coating of electrolytes on the oxide layer of the product

4. Rinsing in warm running water.

5. Drying.

6. Results

Literature

[1] Patent application RU 2543584 C2 C25D 3/22 “Water-based electrolyte for nickel plating of steel, aluminum, titanium, copper and their alloys”.

Claims (3)

1. The method of obtaining a non-porous composite coating on the metal surface of the product, including microarc oxidation of the metal surface and subsequent cathodic electrodeposition of nickel with the formation of a continuous coating, characterized in that the microarc oxidation is carried out in a silicate-phosphate-alkaline electrolyte at an anode direct current density of 5-15 A / dm ² in the voltage range of 300-700 V for 15-60 minutes with the formation of a ceramic oxide coating in the thickness range of 20-60 μm with open porous no more than 15% with an average pore diameter of 15–25 μm, having a predominantly rounded shape and uniformly distributed over the surface, and then cathodic electrodeposition of nickel in a water-based electrolyte is carried out within the pores of the oxide film for 40-60 minutes. 2. The method according to p. 1, characterized in that the cathodic electrodeposition of Nickel is carried out using a non-toxic electrolyte at room temperature. 3. The method according to claim 1, characterized in that the metal surface of the product to be processed is made of aluminum, titanium and their alloys.