RU2751861C1 - Method for obtaining carbon-graphite composite material - Google Patents

Abstract

FIELD: metallurgy, composite materials.SUBSTANCE: invention relates to the field of metallurgy, namely to a method for producing a carbon-graphite composite material impregnated with a melt of a matrix alloy of lead. Vacuum degassing of a porous carbon-graphite billet is carried out in an aqueous solution of a copper electrolyte for 5-7 minutes. A two-layer electroplating coating containing an inner copper layer and an outer layer is applied to the said workpiece. The chamber for impregnation is filled with a molten matrix alloy of lead. A carbon-graphite blank with a galvanic coating is placed in a filled impregnation chamber. The porous billet is impregnated with a melt of a matrix lead alloy under the influence of excessive pressure due to the thermal expansion of the melt when heated at least 100°C above the liquidus temperature of the lead alloy melt. The outer layer of the electroplating is made in the form of a tin-lead layer consisting of, weight percentage: 60 tin and 40 lead deposited by electrolysis from an electrolyte containing 35 g/l of borofluoride tin, 25 g/l of borofluoride lead, 40 g/l of borofluoride acid, 25 ml/l of boric acid, 3 g/l of leather glue and 0.5 g/l of hydroquinone. Filling of the mentioned chamber with the melt of the matrix alloy of lead is carried out by 2/3 and kept at a temperature below the liquidus temperature of the matrix alloy of lead by 15-20°C.EFFECT: quality of composite materials is improved.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 C04B 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.

There is a known method of obtaining 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 C22C 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 workpiece before immersing a porous workpiece in a matrix alloy melt, applying a two-layer galvanic coating on a porous workpiece, consisting of an inner copper and outer nickel layers, impregnating it 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 (RF patent No. 2688772, IPC S22S 47/08, B22F 3/26, publ. 05/22/2019).

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

The task is to develop a method for maximum filling of pores in a carbon-graphite workpiece when impregnated with a matrix alloy.

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 impregnated with a melt of a matrix alloy of lead, including vacuum degassing of a porous carbon-graphite workpiece in an aqueous solution of copper electrolyte for 5-7 minutes, applying a two-layer galvanic coating on it containing an inner copper layer and an outer layer, filling chamber for impregnation of molten matrix alloy of lead placement, carbon and graphite preform with the deposited plated in a filled chamber for impregnation and impregnation of a porous preform molten matrix alloy lead under the influence of excess pressure due to thermal expansion of the melt during heating at least 100 ° C above ^the temperature of the melt liquidus lead alloy, while the outer layer of the galvanic coating is made in the form of a tin-lead layer, consisting of 60 wt.% tin and 40 wt.% lead, deposited by electrolysis from an electrolyte containing 35 g / l of tin hydrofluoric acid o, 25 g / l of hydrofluoric lead, 40 g / l of hydrofluoric acid, 25 ml / l of boric acid, 3 g / l of flesh glue, 0.5 g / l of hydroquinone, and filling the said chamber with a melt of lead matrix alloy is carried out at 2 / 3 and kept at a temperature below the liquidus temperature of the lead matrix alloy by 15-20 ° C.

Dividing the technology into simpler stages: separating the operations of vacuum degassing of a carbon-graphite billet and impregnation, applying a two-layer galvanic coating to the billet prior to impregnation, consisting of an inner copper and an outer layer containing 60 wt.% Tin and 40 wt.% Lead, helps to reduce the impregnation temperature , better wetting of the carbon-graphite framework, increases the permeability of its pores and, accordingly, improves the quality of composite materials (CM).

Simultaneous electrolysis of tin and lead from an electrolyte solution leads to their joint galvanic deposition with the formation of a tin-lead layer on the copper layer of a galvanic coating of a porous workpiece, that is, with the formation of a coating with a given ratio of tin and lead (the ratio of tin and lead is determined by the qualitative and quantitative composition of the electrolyte and electrolysis conditions). Before applying the galvanic coating, the carbon-graphite frame is vacuum degassed in a copper electrolyte, as a result of which the pores are partially filled with electrolyte, after which a copper-plated layer (3-5 microns) is electroplated on the carbon-graphite frame, which is also formed in the pores filled with copper electrolyte. Then the tin-lead coating is applied. This method makes it possible to obtain the alloying effect of the deposited highly pure metals at the interface between the carbon-graphite framework / impregnating alloy and to reduce the value of the wetting angle and surface tension.

The content of 60 wt.% Tin and 40 wt.% Lead in the outer layer of the galvanized coating simplifies the impregnation technology, allowing composites to be obtained at lower temperatures, and also contributes to an increase in the antifriction properties of CM, since by reducing the softening temperature of the galvanic coating, the lead alloy pushes through and seals it deeper into the pores of the carbon-graphite framework.

Impregnation of a porous preform with an electroplated coating applied to it in the melt of the lead matrix alloy in the impregnation chamber leads to better filling of the pores with the matrix alloy.

The application of a copper galvanic sublayer is carried out in a plastic container, which is filled with sulfuric acid copper plating electrolyte, consisting of copper sulfate, distilled water, sulfuric acid, and alcohol.

The application of a tin-lead galvanic layer is carried out in a plastic container, which is filled with an electrolyte consisting of hydrofluoric tin, hydrofluoric lead, hydrofluoric acid (free), boric acid, flesh glue, hydroquinone.

After electroplating, the carbon-graphite frame is placed in an impregnator. In this case, the impregnation chamber, in which a carbon-graphite frame with a layer of galvanic coating deposited on it is placed, allows impregnation of a porous workpiece when heated under the influence of excess pressure of a lead matrix alloy obtained by thermal and thermal expansion of lead with an increase in the volume of the alloy in the closed volume of the device for impregnation.

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 copper electrolyte (aqueous solution), consisting of 200 g / l of copper sulfate, 70 g / l of sulfuric acid and 10-15 ml of alcohol, electrolyte temperature 20-25 ° C ... 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 copper anodes connected with a copper wire are immersed in the container, after which the anodes and the carbon-graphite workpiece are connected to a direct current source, a positive charge to the anodes, and a negative charge to the carbon-graphite workpiece, the current strength is set to 0.5 A / dm ² with a holding time of 30 minutes.

After applying a copper layer of coating to the carbon-graphite frame, the frame is washed in water and a tin-lead coating layer is applied (60 wt.% Tin and 40 wt.% Lead). A carbon-graphite workpiece fixed with a tinned copper wire is immersed in a galvanic chamber filled with an electrolyte (aqueous solution) consisting of tin hydrofluoric acid - 35 g / l, lead hydrofluoric acid - 25 g / l, hydrofluoric acid (free) - 40 g / l, acid boric - 25 ml / l, flesh glue - 3 g / l, hydroquinone - 0.5 g / l, then two anodes from a tin-lead layer (tin 60 wt.%, lead 40 wt.%) connected between a tinned copper wire, the connection to the current source is similar to the copper plating bath. The electrolyte temperature during electrolysis is 20 ° C, the current density is 0.8 - 1 A / dm ² with a holding time of 120 min. After electroplating the carbon-graphite frame, the electroplated carbon-graphite workpiece 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 obtained 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 97 ± 3 189 ± 3 Maximum filling of microscopic pores By prototype method 400 550 five twenty 92 ± 3 181 ± 3 Filling of microscopic pores is incomplete, there are small unopened areas

Thus, a method for producing a carbon-graphite composite material, including vacuum degassing of a porous carbon-graphite workpiece in a copper electrolyte solution, applying a two-layer galvanic coating on it, containing an inner copper layer and an outer tin-lead layer, consisting of 60 wt.% Tin and 40 wt.% lead applied by electrolysis from an electrolyte containing 35 g / l tin hydrofluoric, 25 g / l lead hydrofluoric acid, 40 g / l hydrofluoric acid, 25 ml / l boric acid, 3 g / l flesh glue, 0.5 g / l hydroquinone , placing a carbon-graphite billet with a galvanized coating in an impregnation chamber filled with 2/3 of a matrix alloy melt with a temperature below the liquidus temperature of a lead alloy by 15-20 ° C, and impregnating a porous billet with a lead matrix alloy melt under the influence of excessive pressure due to thermal and thermal expansion of the melt when heated above the liquidus temperature of the lead alloy, improves the quality of the resulting composite materials (CM).

Claims (1)

A method of producing a carbon-graphite composite material, including vacuum degassing of a porous carbon-graphite workpiece in a copper electrolyte solution, applying a two-layer galvanic coating on it containing an inner copper layer, 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 impregnating a porous melt of lead matrix alloy under the influence of excess pressure due to thermal expansion of the melt when heated above the liquidus temperature of the lead alloy, characterized in that the outer layer of the galvanic coating is made of a tin-lead layer, consisting of 60 wt.% tin and 40 wt.% lead, applied by electrolysis from an electrolyte containing 35 g / l of tin hydrofluoric acid, 25 g / l of lead hydrofluoric acid, 40 g / l of hydrofluoric acid, 25 ml / l of boric acid, 3 g / l of flesh glue, 0.5 g / l of hydroquinone, and I place the carbon-graphite billet t into the impregnation chamber, 2/3 filled with a matrix alloy melt with a temperature lower than the liquidus temperature of the lead alloy by 15-20 ° C.