RU2544334C1 - Method of multilayer composite coating manufacturing on steel by chemical deposition - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: under this method on steel surface a multilayer coating is applied, in it nickel-phosphorous layers are applied as odd layers, and cobalt-phosphorous layers are applied as even layers. Ni-P layers are precipitated from the solution with pH 4.1-4.3 and containing: nickel sulphate 10-30 g/l, sodium hypophosphite 15-25 g/l, sodium acetate 10-20 g/l, thiourea 0.005 g/l, acetic acid 13 ml/l. At that Co-P layers are precipitated from solution with pH 8.0-8.5 and containing in g/l: difluoride cobalt 15-35, sodium hypophosphite 10-22, sodium citrate 80-100, ammonium chloride 30-60. The mentioned layers precipitate at temperature 70-92°C.

EFFECT: method ensures making on the steel surface of multilayer composite coatings out of different quantity of alternating layers with increased corrosion resistance and microhardness.

2 cl, 2 tbl, 1 dwg, 4 ex

Description

The invention relates to methods for producing coatings on metal surfaces, in particular to the production of multilayer coatings on steel surfaces by chemical deposition.

A known method of chemical deposition of coatings consisting of cobalt or its alloys (US patent US 2006280860, application US 20050148724, B05D 5/12, C23C 18/34, C23C 18/36). The coating deposition solution comprises a source of cobalt ions, a reducing agent for deposition of cobalt ions, and a stabilizer, which is an oxide. The method is intended to cover parts of microelectronic devices.

A known method of chemical deposition of composite coatings on metal products from a solution containing nanofiber (patent RU 2451113, C23C 18/36, B82B 3/00). Nanofiber is a powder of oxide-hydroxide phases of aluminum with a particle size of 100-700 nm. The composition of the solution, g / l:

nickel sulfate 10-30 sodium hypophosphite 10-20 sodium acetate 10-15 polyvinyl alcohol 0.5-1 nanofiber 0,1-10 distilled water 1 liter

Polyvinyl alcohol is used to stabilize the solution, as well as to maintain the nanofibers in suspension in suspension throughout the deposition process. It is noted that the invention allows to obtain a composite coating having a low coefficient of friction, high wear resistance and high corrosion resistance.

However, all of the above methods require quite complicated preliminary operations for the preparation of powders and fibers, which complicates and increases the cost of the coating process. It also requires preparation of the surface of the parts for applying a chemical coating on it.

A known method for producing a galvanic composite material based on nickel, including electrochemical deposition of a composite material containing nickel, cobalt, fluoroplastic and optionally silicon oxide in the following ratio of solution components (patent RU 2489530, C25D 15/00; patent RU 2489531, C25D 15/00 ):

nickel chloride 200-350 cobalt chloride 2-10 boric acid 25-40 chloramine B 1.5-3.0 silicon oxide 1-30 fluoroplastic emulsion F-4D 7-35

This method allows to obtain fine crystalline, uniform, self-lubricating coatings with high wear resistance and microhardness. However, the presence of silicon oxide in the composition leads to an increase in internal stresses. It is necessary to strictly control the content of silicon oxide in the composition, since an increase in its content above the claimed limit leads to an even greater increase in internal stresses, deterioration in quality, and a decrease in the content below the claimed limit leads to a decrease in the wear resistance of the composite material. In addition, there is several times more hydrogen in galvanic coatings than in coatings obtained by a chemical method, and the presence of hydrogen in coatings reduces their strength characteristics.

The closest analogue of the proposed method is a method of chemical deposition of a composite coating of nickel-phosphorus-cobalt on the surface of alloy steel (patent CN 102433556 China, application CN 20111451578, C23C 18/36, C23C 18/50). The composition of the solution in mass percent:

nickel chloride 5-10 sodium hypophosphite 5-10 cobalt chloride 5-10 ammonium chloride 5-10 lactic acid 1-6 sodium citrate 10-15 complexing agent 0.3-0.5 rare earth element 1-3

In the proposed method, the coating is carried out as follows: the calculated amount of water is added to the reactor, the temperature is increased to 38-42 ° C, stirring is started (stirrer rotation speed is 120 rpm) and the calculated amount of reagents is slowly added in a certain sequence; mixing is carried out until the solution becomes transparent and turns green. This method allows to obtain corrosion-resistant coatings.

All of the above methods offer coating in a single layer, which makes them more susceptible to wear and corrosion than multilayer coatings.

The objective of the present invention is to obtain coatings on steel having high corrosion resistance or microhardness. Moreover, thanks to this method, it should be possible to create a coating, the top layer of which has one of the above characteristics.

To achieve this goal, a method for producing multilayer composite coatings (MCP) by chemical deposition is proposed. MCPs consist of several layers: nickel-phosphorus and cobalt-phosphorus. The first layer of MCP is deposited on a steel surface, and subsequent layers on a composite metal-phosphorus surface. The coating interacts with the surface to be coated by restoring metal ions on it to metal and the interaction of metal ions with phosphorus on it.

The cobalt-phosphorus layer is deposited from chemical cobalt solutions in which cobalt difluoride is the source of cobalt ions. This type of solution has not previously been used to obtain coatings. For the preparation of a chemical cobalt solution, cobalt difluoride can be used, which is a waste of the fluoroplast processing process (application RU 2011149496, B29B 17/00).

Cobalt difluoride is an inorganic substance, a salt of cobalt and hydrofluoric acid. Under normal conditions, cobalt difluoride is a pink-red crystalline substance that is soluble in water. It is usually used as an intermediate in the preparation of cobalt trifluoride, complex cobalt (III) fluorides, and cobalt (IV). It is used in the production of cathodes for chemical current sources, as a component of laser materials and as a catalyst in the production of fluorocarbons.

In the process of processing fluoroplastics by thermal degradation with exhaustive fluorination (application RU 2011149496), cobalt trifluoride can be used as a fluorinating agent. When heated, cobalt trifluoride decomposes into fluorine, which is involved in exhaustive fluorination, and cobalt difluoride, which is a waste product.

Chemical deposition of cobalt and phosphorus on the surface of metallic materials gives them ferromagnetic properties, as well as high microhardness. Of particular importance is the deposition of this coating on thin magnetic films used to create microelectronic devices.

Chemically precipitated nickel has high corrosion-protective properties and low porosity. Thus, the nickel-phosphorus coating can be used on metal products of complex profile, on large-sized fittings, to increase the wear resistance of the rubbing surfaces of machine parts; to increase corrosion resistance in a medium of boiling alkali and superheated steam; to replace the chrome coating, to use cheaper steel instead of corrosion-resistant steel, coated with a layer consisting of nickel and phosphorus.

The technical result obtained due to the use of the proposed method is that coatings are obtained having high microhardness and corrosion resistance. Corrosion resistance is increased as a result of the presence of several dense layers of corrosion-resistant nickel. The microswitching of coatings increases as a result of the presence of even cobalt-phosphorus layers, the physical properties of which, in particular hardness, exceed those similar to those for the nickel-phosphorus layer. The application of alternating layers allows you to vary the characteristics of the resulting coating. In the event that the nickel-phosphorus layer is last applied, the coating has enhanced corrosion resistance; if the last layer is cobalt-phosphorus, the coating has a high microhardness.

Method Description

The odd layers - nickel-phosphorus coatings - are deposited on the steel surface (for the first MCP layer) and on the cobalt-phosphorus composite surface (for subsequent layers) from solutions that have the following composition:

nickel sulfate 10-30 g / l sodium hypophosphite 15-25 g / l sodium acetate 10-20 g / l thiourea 0.005 g / l acetic acid 13 ml / l

Coating mode: pH 4.1-4.3, temperature 70-92 ° C; time 60 min., the speed of mixing the solution during coating can be from 60 rpm

The nickel-phosphorus coating deposition rate is 12-15 μm / h.

The deposition of odd layers - cobalt-phosphorus coatings - is carried out on the composite surface of nickel-phosphorus from solutions that have the following composition, g / l:

cobalt difluoride 15-35 sodium hypophosphite 10-22 sodium citrate 80-100 ammonium chloride 30-60

Coating mode: pH 8.0-8.5, temperature 70-92 ° C; time 60 min., the speed of mixing the solution during coating can be from 60 rpm

The cobalt-phosphorus coating deposition rate is 5-7 μm / h.

The following are examples of the implementation of the claimed method.

Example 1. 10 g of nickel sulfate and 20 g of sodium acetic acid are poured into a measuring bowl and 13 ml of 99.7% glacial acetic acid are added. The substances are dissolved in distilled water, the solution is brought to a volume of 1 liter and stirred (60 rpm). The pH of the solution should correspond to 4.1-4.3. The resulting solution was poured into a bath for chemical precipitation and heated. After the solution reaches a temperature of 85 ° C, pre-activated samples of St3 steel are lowered into it, then 0.005 g of thiourea are poured, after which 25 g of hypophosphite sodium are added. The solution was stirred (60 rpm). Stirring is continued throughout the coating process. The temperature of the solution throughout the process should be in the range of 90 ± 2 ° C. The exposure time of the samples is 1 hour.

The study of the coatings obtained after applying the first layer by scanning electron microscopy (SEM) with a magnification of 10,000 times showed that the particle size in the nickel-phosphorus layer is 40-1000 nm.

After completion of the process, samples of St3 steel coated with a nickel-phosphorus layer are placed in solution without intermediate operations to obtain a cobalt-phosphorus composite coating.

For this solution, 35 g of cobalt difluoride, 45 g of ammonium chloride and 80 g of sodium citrate are poured into measuring dishes. The substances are dissolved in distilled water, the solution is brought to a volume of 1 liter and stirred (60 rpm). After complete dissolution, the pH of the solution is adjusted to 8-8.5 with ammonium hydroxide. The resulting solution was poured into a bath for chemical precipitation and heated. After the solution reaches a temperature of 85 ° C, samples are lowered into it, and 20 g of hypophosphite sodium are poured. The solution was stirred (60 rpm). Stirring is continued throughout the coating process. The temperature throughout the process should be in the range of 90 ± 2 ° C. The exposure time of the samples is 1 hour, after which the parts are washed in cold water and dried to constant weight.

The study of the obtained coatings after applying the second layer by SEM with an increase of 5500 times showed that the particle size in the cobalt-phosphorus layer is 500-1200 nm.

Example 2. The first layer — a nickel-phosphorus composite coating — is obtained analogously to example 1. After the application of 1 layer, samples of St3 steel coated with a nickel-phosphorus layer are placed in a solution without intermediate operations to obtain a cobalt-phosphorus composite coating.

For this solution, 28.6 g of cobalt difluoride, 45 g of ammonium chloride and 93.6 g of sodium citrate are poured into measuring dishes. The substances are dissolved in distilled water, the solution is brought to a volume of 1 liter and stirred (60 rpm). After complete dissolution, the pH of the solution is adjusted to 8-8.5 with ammonium hydroxide. The resulting solution was poured into a bath for chemical precipitation and heated. After the solution reaches a temperature of 85 ° C, samples are lowered into it, and 21 g of sodium hypophosphite is poured. The solution was stirred (60 rpm). Stirring is continued throughout the coating process. The temperature throughout the process should be in the range of 90 ± 2 ° C. The exposure time of the samples is 1 hour, after which the parts are washed in cold water and dried to constant weight.

The study of the obtained coatings after applying the second layer by SEM with an increase of 6,000 times showed that the particle size in the cobalt-phosphorus layer is 800-5100 nm.

Example 3. The first layer, a nickel-phosphorus composite coating, is prepared analogously to example 1. After the application of 1 layer, samples of St3 steel coated with a nickel-phosphorus layer are placed in a solution without intermediate operations to obtain a cobalt-phosphorus composite coating.

For this solution, 35 g of cobalt difluoride, 45 g of ammonium chloride and 80 g of sodium citrate are poured into measuring dishes. The substances are dissolved in distilled water, the solution is brought to a volume of 1 liter and stirred (60 rpm). After complete dissolution, the pH of the solution is adjusted to 8-8.5 with ammonium hydroxide. The resulting solution was poured into a bath for chemical precipitation and heated. After the solution reaches a temperature of 85 ° C, samples are lowered into it, and 10 g of hypophosphite sodium are poured. The solution was stirred (60 rpm). Stirring is continued throughout the coating process. The temperature throughout the process should be in the range of 90 ± 2 ° C. The exposure time of the samples is 1 hour, after which the parts are washed in cold water and dried to constant weight.

The study of the obtained coatings after applying the second layer by SEM with an increase of 7500 times showed that the particle size in the cobalt-phosphorus layer is 300-2030 nm.

Example 4. The first layer, a nickel-phosphorus composite coating, is prepared analogously to example 1. After the application of 1 layer, samples of St3 steel coated with a nickel-phosphorus layer are placed in a solution without intermediate operations to obtain a cobalt-phosphorus composite coating.

For this solution, 35 g of cobalt difluoride, 45 g of ammonium chloride and 100 g of sodium citrate are poured into measuring dishes. The substances are dissolved in distilled water, the solution is brought to a volume of 1 liter and stirred (60 rpm). After complete dissolution, the pH of the solution is adjusted to 8-8.5 with ammonium hydroxide. The resulting solution was poured into a bath for chemical precipitation and heated. After the solution reaches a temperature of 85 ° C, samples are lowered into it, and 10 g of hypophosphite sodium are poured. The solution was stirred (60 rpm). Stirring is continued throughout the coating process. The temperature throughout the process should be in the range of 90 ± 2 ° C. The exposure time of the samples is 1 hour, after which the parts are washed in cold water and dried to constant weight.

The study of the obtained coatings after applying the second layer by SEM with an increase of 13,000 times showed that the particle size in the cobalt-phosphorus layer is 400-1400 nm.

The drawing shows the dependence of the change in the specific gravity of the MCP obtained by testing the coatings for corrosion resistance. The tested MCP consist of two layers, the first layer is obtained from a solution, the composition of which is shown in table 1, the second layer is from a solution, the composition of which is shown in table 2.

Corrosion resistance tests were carried out by keeping suspended samples in a 3% solution of sodium chloride at a temperature of 18-20 ° C (according to GOST 9.308-85 Unified corrosion and aging protection system. Metallic and nonmetallic inorganic coatings. Accelerated corrosion test methods). After a certain time, the samples were removed from the solution, dried, weighed, and the change in mass was determined.

Table 1 Solution component amount nickel sulfate 10 g / l sodium hypophosphite 25 g / l sodium acetate 20 g / l thiourea 0.005 g / l acetic acid 13 ml / l

table 2 No. of solution The composition of the solution, g / l cobalt difluoride sodium hypophosphite sodium citrate ammonium chloride one 35 twenty one hundred 45 2 35 twenty 80 45 3 35 10 80 45 four fifteen 10 80 45 5 fifteen 10 one hundred 45 6 fifteen twenty one hundred 45 7 35 10 one hundred 45 8 fifteen twenty 80 45

Claims (2)

1. A method of obtaining a multilayer composite coating on a steel surface by chemical deposition, including the preparation of solutions for applying odd layers of nickel-phosphorus and solutions for applying even layers of cobalt-phosphorus, applying layers of nickel-phosphorus, applying layers of cobalt-phosphorus, the first layer of nickel -phosphorus is deposited on a steel surface, and the subsequent odd layers are applied to a composite surface of cobalt-phosphorus at a pH of 4.1-4.3, a temperature of 70-92 ° C from a solution of the composition:
nickel sulfate 10-30 g / l sodium hypophosphite 15-25 g / l sodium acetate 10-20 g / l thiourea 0.005 g / l acetic acid 13 ml / l
and cobalt-phosphorus layers are deposited on a nickel-phosphorus composite surface at pH 8.0-8.5, temperature 70-92 ° C from a solution of the composition, g / l:
cobalt difluoride 15-35 sodium hypophosphite 10-22 sodium citrate 80-100 ammonium chloride 30-60 2. The method according to p. 1, characterized in that the said solutions from the moment of loading the coated surfaces in them are mixed with a speed of at least 60 rpm.