RU2618679C1 - Method of obtaining composite electrochemical coating on steel - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves the preparation of a solution for depositing a nickel-phosphorus layer and an electrolyte for depositing a cobalt-polytetrafluoroethylene layer, depositing a nickel-phosphorus layer at a pH of 4.5-5.0, a temperature of 90°C, the deposition time is 30 minutes from a solution of the composition:⋅ NiSO₄⋅7H₂O⋅30 g/l⋅, NaH₂PO₂⋅H₂O 10 g/l, Na(CH₃COO) of 10 g/l and a layer of cobalt-polytetrafluoroethylene, which is deposited on the composite surface of nickel-phosphorus at pH 2-5, temperature 18-90°C, current density 6.25 A/dm², deposition time of 20-30 min in the electrolyte on the basis of the mother liquor of the process of synthesis of fluoroplastic MP F-4D: CoF₂⋅4H₂O⋅119 g/l, Na₂SO_{4 nowater}⋅36 g/l, H₃BO₃⋅45 g/l.

EFFECT: invention makes it possible to obtain a uniform coating on the steel, having increased hardness, strength and wear resistance at a low consumption of the composite material.

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Description

The invention relates to the field of electroplating, in particular to the electrolytic deposition of hard wear-resistant coatings and to methods for producing a composite electrochemical coating based on waste fluoropolymers.

To date, a special place among galvanic composites is occupied by metal-polymer, and in particular metal-fluoroplastics, which have a number of characteristics typical of both metals (strength, wear resistance) and fluoropolymers (sealing ability, anti-adhesiveness and non-stickness). These coatings have high corrosion resistance and low coefficient of friction.

The prior art method of deposition of a composite electrochemical coating (CEC) with the inclusion of a dispersed phase (DF) (for example, tungsten carbide, vanadium carbide and others) in a metal matrix at a constant or asymmetric current with an asymmetry coefficient of 1.2-6, at an electrolyte temperature 40-60 ° C, cathodic current density of 35-40 A / dm ² , the pH of the electrolyte is 0.5-0.8 using an electrolyte containing, g / l:

ferric chloride (II) 500-600 hydrochloric acid 0.5-1.5

Coatings obtained from an electrolyte have high microhardness (up to 11–13 GPa) and wear resistance (8–20 times higher than “pure” iron coatings and hardened alloy steels 20–60 times), adhesion to the base (300–400 MPa) is ensured high deposition rate of the coating (up to 1 mm / hour). However, the residual internal tensile stresses and cracks caused by electrolysis lead to a decrease in the resistance of parts with coatings to cyclic loads, which reduces their fatigue strength [RF patent No. 2478739 Method for the electrochemical production of composite nickel coatings with quasicrystalline particles. IPC C25D 15/00, publ. 04/10/2013, application No. 20111150538/02 dated 12/13/2011].

A known method of applying to the steel parts of the first layer, its heat treatment, applying the second layer, its heat treatment, after which the second layer is machined, the first and second layers are applied from the same aqueous suspension consisting of aluminum-chromophosphate solution and aluminum powder [RF patent No. 2510716. The method of applying a protective coating to steel parts. С23С 22/00, application No. 2012131893/02 of 07.25.2012].

An aqueous suspension is prepared from the following components, wt. %:

chromium (III) salt in terms of chromium 0.6-0.9 sodium or potassium hydroxide 1.8-2.6 aluminum hydroxide 17.3-24.0 orthophosphoric acid 17.3-24.0 chromic anhydride 6.9-9.3 aluminum powder 54.4-68.0 water to a specific gravity of aluminochromophosphate solution 1.20-1.30 g / cm ³

The disadvantage of this method is the high temperature regime of obtaining coatings from 60-200 ° C, as well as rather complicated preliminary operations for sample preparation for sequential deposition of layers.

The prototype of the invention is the method described in the patent of the Russian Federation No. 2352693 (Electroplated composite material based on nickel. C25D 15/00, publ. 04/20/2009, application No. 20088110628/02 of 03.19.2008). According to this method, the composite material nickel-fluoroplast was obtained by the electrochemical method from an electrolyte of the following composition, g / l:

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

Electrolysis modes: pH 1.0-5.5, temperature 18-40 ° C, cathodic current density 0.5-12.0 A / dm ² with stirring.

The chemical composition of the composite material,%:

Nickel 98.7 Cobalt 0.6 Ftoroplast 0.7

The presence of cobalt in nickel coatings can increase the wear resistance of coatings.

Nickel is a good structural material, and therefore it is of great importance to develop coatings based on it that have high wear resistance and a low coefficient of friction. In this regard, a nickel-based material was developed in the form of a nickel-boron alloy, which has high hardness and wear resistance (copyright certificate No. 1387528 was obtained). In order to increase the wear resistance of the nickel-boron alloy, it was proposed to additionally introduce fluoroplastic (the so-called "self-lubricating material") into the coating, which forms a thin fluoroplastic film on the surface of composite coatings nickel-boron-fluoroplast and nickel-fluoroplastic as a result of friction of two surfaces friend and crushing of the fluoroplastic in the coating (obtained RF patent No. 2213812, Electrolyte for deposition of the composite coating nickel-boron-fluoroplastic. C25D 15/00, publ. 10.10.2003, application No. 2002113832/02 of 05.27.2002; and p Awning RF №2213813 electroplating composite material based on nickel, publ. 10.10.2003. Application №2002113887 / 02 dated 27.05.2002). However, due to the fact that the coating usually does not have a perfectly smooth surface, a harder coating in the latter case with its projections should destroy the self-lubricating material, which is formed on the coating surface in the form of fluoroplastic with a higher speed, and thereby reduce the wear resistance of coatings and their coefficient friction. Therefore, it was proposed in order to increase the wear resistance of coatings and reduce the coefficient of friction to apply not nickel-boron-fluoroplast, nickel-fluoroplast, but composite coatings nickel-cobalt-fluoroplastic to rubbing articles, since coatings when cobalt is introduced into the coating are more finely crystalline and uniform.

The disadvantages of the prototype are: significantly lower hardness of the coating compared with the coating obtained by the claimed method; composite material consumption is higher than in the claimed method.

The technical result of the proposed method is

- obtaining uniform coatings with high wear resistance;

- increase hardness due to the multilayer coating;

- reducing the amount of waste production fluoropolymers.

This allows you to expand the scope of applicability of steel parts with this coating, to create a low-waste technology for the production of fluoropolymers.

Disclosure of invention

The essence of this invention is a method for producing a coating on steel from waste products of fluoropolymers, with increased hardness, strength, wear resistance at low consumption of composite material.

This problem is solved by the proposed method for producing a composite electrochemical coating from an electrolyte containing, as a dispersed phase, polytetrafluoroethylene nanoparticles present in the mother liquor of the synthesis process of fluoroplastic grade F-4D (MP F-4D), with the addition of boric acid (H ₃ BO ₃ ) .

MP F-4D is separated from the finished product and remains in the reactor. The mother liquor is a clear solution with a suspended particle content of 0.24 g / l. It contains polyfluorine derivatives of hydrocarbons, as well as a small amount of ammonium ions (0.019 g / l), fluorides (up to 31.3 g / l).

The essence of the method is as follows.

A nanofilm of an electrolyte containing a nickel or cobalt salt dissolved in the liquid waste of the polytetrafluoroethylene synthesis process is deposited on the metal surface, and a cobalt (II) salt is obtained by extraction (isolation) from the catalyst waste of the ultrafine polytetrafluoroethylene synthesis process.

The experiment was carried out on steel samples of grade 30HGSA. Before electrochemical coating, fat contaminants and metal oxides were sequentially removed from the samples. For this, the samples were degreased in a solution of sodium hydroxide (25 g / l) and sodium carbonate (25 g / l) at a temperature of 90 ° C for 20 minutes. Then the samples were washed with hot water. Then the oxides were removed by etching in a solution of H ₂ SO ₄ (200 g / l) with the addition of urotropine (30 g / l), after which they were washed with cold water. The next step was the deposition of heterogeneous layers of metals containing, along with metals, polytetrafluoroethylene nanoparticles, which are the dry residue of the mother liquor. Chemical and electrochemical methods were used to deposit heterogeneous metal - polytetrafluoroethylene films.

Example 1. The first layer contained nickel-phosphorus. Steel samples were first immersed in an aqueous solution, g / l:

NiSO ₄ ⋅7H ₂ O thirty NaH ₂ PO ₂ ^⋅ H ₂ O 10 Na (CH ₃ COO) 10 pH 4,5-5

Temperature - plus 90 ° C

The deposition time is 30 minutes.

The particle size of the metal ranged from 2.444 to 9.660 μm. The layer thickness was 0.0079 g / cm ² , the microhardness of the coating was 2000 kgf / mm ² .

The second layer contained nickel-phosphorus-cobalt polytetrafluoroethylene. Samples coated with nickel-phosphorus were immersed in an electrolyte, g / l:

NiCl ₂ ⋅ 6H ₂ O 31 CoF ₂ ⋅ 4H ₂ O eighteen NaH ₂ PO ₂ ⋅H ₂ O twenty CS (NH ₂ ) ₂ 0.005 NH ₄ Cl thirty pH 5-6

Process temperature - plus 90 ° C.

The deposition time is 30 minutes.

The cobalt difluoride salt was preliminarily isolated from the solid waste of the catalyst for the process of thermal decomposition of polytetrafluoroethylene. Solid waste is a mixture of polytetrafluoroethylene, cobalt trifluoride and cobalt difluoride.

The formation of a composite chemical coating. The particle size of the metal ranged from 0.786 to 7.837 microns. The microhardness of the coating was 2500 kgf / mm ² .

Example 2. The first layer is a composite coating of nickel-phosphorus, obtained analogously to example 1. After the application of the layer of nickel-phosphorus, the sample is immersed in electrolyte, g / l

CoF ₂ ⋅ 4H ₂ O 119 Na ₂ SO _{4 anhydrous.} 36 H ₃ BO ₃ 45 pH 2-3

The current density of 6.25 A / DM ²

The process temperature is plus 18-20 ° C.

The deposition time is 20 minutes.

The study of the obtained coatings showed that the microhardness was 1690 kgf / mm ² .

Example 3. The first layer contained nickel-phosphorus. Steel samples were first immersed in an electrolyte, g / l:

NiSO ₄ ⋅7H ₂ O thirty NaH ₂ PO ₂ ⋅H ₂ O 10 Na (CH ₃ COO) 10 pH 4,5-5

The current density is 2.5-4.5 A / dm ² .

Temperature - plus 90 ° C.

Precipitation time 30 minutes.

The particle size of the metal ranged from 2.474 to 9.660 microns. The layer thickness was 0.0079 g / cm ² , the microhardness of the coating was 2000 kgf / mm ² .

The second layer contained nickel-phosphorus-cobalt polytetrafluoroethylene. The coating was applied by electrochemical method. Samples were immersed in an electrolyte prepared on the basis of MP Ф - 4Д, the composition of which is indicated above, g / l:

CoF ₂ ⋅ 4H ₂ O 119 Na ₂ SO _{4 starvation} 36 H ₃ BO ₃ 45 pH 2-3

The current density is 6.25 A / dm ² .

The process temperature is plus 18-20 ° C.

The deposition time is 20 minutes.

Composite electrochemical coating with a microhardness of 2550 kgf / mm ² .

A composite nanocrystalline coating having an even fine crystalline surface was heat treated for 3 minutes at a temperature of 410-425 ° C, followed by cooling to room temperature.

Claims (4)

A method of obtaining a composite electrochemical coating on a steel surface by sequential deposition of coating layers, comprising preparing a solution for applying a nickel-phosphorus layer and an electrolyte for applying a cobalt-polytetrafluoroethylene layer, deposition of a nickel-phosphorus layer at pH 4.5-5.0, temperature 90 ° C , the deposition time of 30 min from a solution of the composition: NiSO ₄ ⋅7H ₂ O 30 g / l NaH ₂ PO ₂ ⋅H ₂ O 10 g / l Na (CH ₃ COO) 10 g / l and a cobalt-polytetrafluoroethylene layer, which is deposited on the nickel-phosphorus surface at pH 2-5, temperature 18-90 ° C, current density 6.25 A / dm ² , deposition time 20-30 minutes in the electrolyte based on the mother liquor of the synthesis process fluoroplastic MP F - 4D: CoF ₂ ⋅ 4H ₂ O 119 g / l Na ₂ SO _{4 anhydrous} 36 g / l H ₃ BO ₃ 45 g / l