RU2750300C1 - Method for producing carbon-graphite composite material - Google Patents

Abstract

FIELD: metallurgy, composite materials.

SUBSTANCE: invention relates to the field of metallurgy, namely the creation of composite materials by impregnating a porous frame. The method for producing a carbon-graphite composite material includes vacuum degassing of a porous carbon-graphite billet in an electrolyte solution, applying a four-layer electroplated coating to it, impregnating it with a melt of a matrix lead alloy under the influence of excessive pressure due to thermal expansion of the melt when heated above the liquidus temperature of the lead alloy, while vacuum degassing is carried out in a solution of a nickel electrolyte containing 140 g/l of nickel sulfate, 50 g/l of sodium sulfate, 30 g/l of magnesium sulfate, 20 g/l dry boric acid, and the electroplated coating is performed by successive application of the inner nickel, intermediate zinc and silver and outer copper layers.

EFFECT: higher quality of composite materials, in particular, increased compressive strength.

1 cl, 1 tbl

Description

The invention relates to the field of metallurgy, namely to the creation of composite materials by impregnation of a porous frame with high electrical conductivity, antifriction properties, resistance in aggressive environments.

A known method of producing a composite material by impregnation with simultaneous chemical action. The workpiece is installed on a special graphite platform, heated over the surface of a silicon melt or an alloy based on silicon and copper, having a temperature of 1700-1800 ° C, then gradually, at a speed of no more than 10 cm / min, the workpiece is lowered into a bath with a melt. Thereby, carrying out impregnation with a unidirectional melt flow, propagating by the front along the entire section of the workpiece (RF patent No. 2276631 IPC С04В 35/52, publ. 02.08.2004).

The disadvantage of this method is the absence of the stage of evacuation of both the alloy and the workpiece during the impregnation process, as a result of which various impurities in the pores of the carbon-graphite workpiece prevent them from filling with the matrix alloy, and the lack of evacuation negatively affects the melt of the matrix alloy, which oxidizes, interacting with air, reducing the quality of the composite material.

A known method of producing a composite material by impregnating a porous workpiece with metal, in which the reinforcing porous frame is preheated, then poured with a matrix alloy, vacuum degassing is carried out and impregnated under the influence of an excess pressure of 15 ± 3 MPa on the workpiece due to thermal expansion of the melt in a closed volume of the vessel during heating (RF patent No. 1759932, IPC S22S 1/09, B22F 3/26, publ. 07.09.92).

The disadvantage of this method when it is used to obtain CM by impregnation is the limitation of the nomenclature of metals for their use as a matrix alloy, only lead or its alloys.

The closest is a method for producing a carbon-graphite composite material, including vacuum degassing of a porous carbon-graphite workpiece in an electrolyte solution, applying a three-layer galvanic coating on it, consisting of inner copper, intermediate chromium and silver, and outer nickel layers, and impregnating the porous workpiece with a melt of lead matrix alloy under exposure to excess pressure due to thermal expansion of the melt when heated above the liquidus temperature of the lead alloy (RF patent No. 2688778, IPC B22F 3/26, C22C 1/08, B60L 5/00, publ. 05/22/2019).

The disadvantage of this method is the need for impregnation at high temperatures and pressures.

The technical result of the invention is to improve the quality of composite materials (CM).

The technical result is achieved in a method for producing a carbon-graphite composite material, including vacuum degassing of a porous carbon-graphite workpiece in an electrolyte solution, applying a four-layer electroplating coating on it, consisting of copper, silver and nickel layers, placing a carbon-graphite workpiece with an applied galvanic coating in a melting chamber, filling the chamber matrix alloy and impregnation of the workpiece with a melt of a matrix alloy of lead under the influence of excessive pressure due to thermal expansion of the melt when heated above the liquidus temperature of the lead alloy, while vacuum degassing is carried out in a solution of nickel electrolyte containing 140 g / l of nickel sulfate, 50 g / l of sodium sulfate , 30 g / l of magnesium sulfate, 20 g / l of dry boric acid, the galvanic coating contains a zinc layer and is made of successively applied inner nickel, intermediate zinc and silver, and outer copper layers, and carbon The aphyte workpiece is placed in a 2/3 impregnation chamber filled with a matrix alloy melt with a temperature below the liquidus temperature of the lead alloy by 15-20 ° C.

Dividing the technology into simpler stages: separating the operations of vacuum degassing of a carbon-graphite workpiece and impregnation, applying a four-layer galvanic coating to the workpiece before impregnation, consisting of an inner nickel, intermediate zinc and silver layers, and an outer copper layer, contributes to better wetting of the carbon-graphite frame, filling its pores and, accordingly, improves the quality of composite materials (CM).

Before electroplating a nickel layer, vacuum degassing of the carbon-graphite frame is carried out in a nickel electrolyte, as a result of which the pores are partially filled with electrolyte, after which a nickel layer is electroplated on the carbon-graphite frame, which is also formed in the pores filled with electrolyte, then zinc, silver and external copper coating, which prevents the pyroelectric effect when the molten metal and the carbon-graphite frame come into contact with galvanic coatings, as a result of which the matrix lead alloy assimilates alloying components to a greater extent and receives the alloying effect of the deposited high-purity metals at the frame / impregnation interface and a decrease in the contact angle wetting.

Impregnation of a porous workpiece, with a four-layer galvanic coating applied to it, in a melt of a lead matrix alloy located in an impregnation chamber made of VT1-0 titanium leads to better filling of the pores with a matrix alloy.

Electroplating is carried out in plastic containers, which respectively fill:

- for applying a nickel coating layer - nickel sulfate electrolyte consisting of nickel sulfate, sodium sulfate, magnesium sulfate, dry boric acid;

- for applying a zinc coating layer - sulfate electrolyte, consisting of zinc oxide and alkali;

- for applying a silver coating layer - sulfate electrolyte, consisting of silver chloride, iron cyanide potassium, soda ash;

- for applying a copper coating layer - pyrophosphate copper plating electrolyte, consisting of copper sulfate, sodium pyrophosphate, two substituted sodium pyrophosphate.

After electroplating, the carbon-graphite frame is placed in an impregnator. In this case, the impregnation chamber, into which a carbon-graphite frame with an electroplated coating applied to it, is placed, makes it possible to impregnate a porous workpiece when heated under the influence of excess pressure of the lead matrix alloy obtained by thermal expansion of lead with an increase in the volume of the alloy in the closed volume of the impregnation device.

Determination of the liquidus temperature with overheating allows one to take into account the amount of heating, ensures the creation of the required impregnation pressure, which makes it possible to obtain high-quality CM with a high degree of filling the volume of open pores of a porous workpiece with a matrix alloy.

The use of a lead alloy as a matrix melt, and a carbon-graphite billet as a porous body makes it possible to obtain composite materials that are widely used in mechanical engineering for the manufacture of guides, seals, and plain bearing shells.

According to the proposed method, KM carbon graphite was obtained - a lead alloy using carbon graphite grade AG-1500, having an open porosity of 15%. The carbon graphite sample was made in the form of a cube with a side of 30 mm. Thus, the volume of the carbon-graphite framework was 900 mm ³ , the pore volume in the framework was 135 mm ³ .

A carbon-graphite workpiece, fixed with a copper wire, is immersed in a galvanic chamber filled with nickel electrolyte (aqueous solution), consisting of 140 g / L of nickel sulfate, 50 g / L of sodium sulfate, 30 g / L of magnesium sulfate, 20 g / L of dry boric acid ... Then the container is covered with a sealed dome, after which vacuum degassing is carried out through the hole in the dome for 5-7 minutes using a vacuum pump. Next, two nickel anodes are immersed in the container, interconnected by a copper wire, after which the anodes and the carbon-graphite workpiece are connected to a direct current source, the current strength is set at 2 A / dm ² with a shutter speed of 40-60 minutes.

After applying a nickel coating layer, the carbon-graphite framework is washed in hot water and a zinc layer is applied. For this, the capacity of the galvanic chamber is filled with an alkaline zinc electrolyte (aqueous solution) consisting of 10 g / l of zinc oxide, 100 g / l of potassium alkali. A carbon-graphite workpiece fixed on a low-carbon wire is immersed in a galvanic bath. Then, anodes made of zinc connected to each other by a wire made of low-carbon steel are installed in the galvanic bath. The DC connection is similar to a nickel plating bath. The current strength is set at 2-3 A / dm ² with an exposure time of 40 minutes. The degassing process is not repeated.

Next, the carbon-graphite frame is washed with hot water, and a silver coating layer is applied. For this, the capacity of the galvanic chamber is filled with silvering electrolyte (aqueous solution), consisting of 20 g / l of silver chloride, 45 g / l of yellow blood salt (iron cyanide potassium), 50 g / l of soda ash. A carbon-graphite workpiece fixed on a copper wire is immersed in a galvanic bath. Then anodes made of graphite, interconnected by copper wire, are installed in the galvanic bath. The DC connection is similar to a nickel plating bath. The current strength is set at 0.2 A / dm ² with an exposure of 40 minutes at an electrolyte temperature of 20 ° C.

Next, the carbon-graphite frame is washed with hot water, and a copper coating is applied. For this, the capacity of the galvanic chamber is filled with pyrophosphate copper plating electrolyte (aqueous solution), consisting of 35 g / l of copper sulfate, 130 g / l of sodium pyrophosphate, 90 g / l of dibasic sodium pyrophosphate. Copper anodes are installed in the bath. The current strength is set at 0.5 A / dm ² with an exposure of 60 minutes at an electrolyte temperature of 30 ° C.

Next, a carbon-graphite billet with a four-layer electroplated coating is washed in water and dried.

The chamber for impregnating the carbon-graphite billet is made of VT1-0 titanium. The impregnation chamber is heated to a temperature of 150 ° C and filled 2/3 with a molten lead alloy. Withstand the lead melt until it reaches a temperature below the liquidus temperature of the lead alloy by 15-20 ° C. In the impregnation chamber on the crystallized (as a result of cooling) surface, place a carbon-graphite workpiece with an applied galvanic coating. Then, lead melt is added to the impregnation chamber, completely covering the porous workpiece with it. The chamber is closed with a lid, the melt of the matrix alloy is added to the conical filler hole in the lid, rubbed in with a stopper preheated to 500 ° C, and pinned.

After sealing, the chamber for impregnating the carbon-graphite workpiece is heated at least 100 ° C above the liquidus temperature of the lead matrix alloy melt with isothermal holding for 20 minutes when the specified temperature and design pressure are reached.

Due to the difference in the coefficients of thermal expansion of the container and the melt of the lead matrix alloy, as well as due to the difference in the coefficients of thermal (during the melting of lead) expansion of lead, at which the volume of the melt in the chamber increases, an optimal impregnation pressure is created.

The impregnation was carried out at a pressure of 3 MPa, which was ensured by the heating temperature of the impregnation chamber, equal to 450 ° C. At the end of the impregnation, the resulting CM is removed and cooled with crystallization of the melt of the lead matrix alloy in the pores.

The resulting CM was tested for compressive strength, the degree of filling of open pores (impregnation density) was estimated by the specific gravity of CM before and after impregnation, the CM structure was estimated from the results of metallographic studies. The test results are shown in the table.

Table

Composite material Impregnation start temperature, С Temperature at the end of impregnation, С Impregnation pressure, MPa Pressure holding time, min. The degree of filling of open pores,% Compressive strength of CM, MPa Results of metallographic studies According to the proposed method 150 450 3 twenty 95 ± 2 111 ± 2 Maximum filling of microscopic pores By prototype method 400 550 five twenty 82 ± 2 95 ± 2 Microscopic pore filling is incomplete

Thus, a method for producing a carbon-graphite composite material, including vacuum degassing of a porous carbon-graphite workpiece in a nickel electrolyte solution containing 140 g / L of nickel sulfate, 50 g / L of sodium sulfate, 30 g / L of magnesium sulfate, 20 g / L of dry boric acid, applying a galvanic coating on it, containing an inner nickel, intermediate zinc and silver, and an outer copper layers, placing a carbon-graphite blank with a galvanized coating in an impregnation chamber for 2/3 filled with a matrix alloy melt with a temperature below the liquidus temperature of a lead alloy by 15-20 ° C and impregnation of the workpiece with a melt of a lead matrix alloy under the influence of excessive pressure due to thermal expansion of the melt when heated above the liquidus temperature of the lead alloy provides an increase in the quality of composite materials (CM).

Claims (1)

A method of obtaining a carbon-graphite composite material, including vacuum degassing of a porous carbon-graphite workpiece in an electrolyte solution, applying a four-layer galvanic coating on it containing copper, silver and nickel layers, placing a carbon-graphite workpiece with an applied galvanic coating in a chamber for impregnation, filling the chamber with a melt of a matrix alloy and billets with a melt of a lead matrix alloy under the influence of excessive pressure due to thermal expansion of the melt when heated above the liquidus temperature of a lead alloy, characterized in that vacuum degassing is carried out in a nickel electrolyte solution containing 140 g / l of nickel sulfate, 50 g / l of sodium sulfate, 30 g / l of magnesium sulfate, 20 g / l of dry boric acid, the galvanic coating contains a zinc layer and is made by sequential deposition of the inner nickel, intermediate zinc and silver and outer copper layers, and the carbon-graphite blank is placed into the impregnation chamber, 2/3 filled with a matrix alloy melt with a temperature below the liquidus temperature of the lead alloy by 15-20 ° C.