RU2744923C1 - Method for producing carbon-carbon composite material on pitch matrices - Google Patents

Abstract

FIELD: mechanical engineering.

SUBSTANCE: invention relates to the field of mechanical engineering and the production of carbon-carbon composite materials (CCCM), which can be used to complete heavily loaded friction units under conditions of high energy loading and an oxidizing environment. The method for producing a carbon-carbon composite material includes annealing of the initial molded blanks based on carbon fibers and pitch binders, subsequent intermediate high-temperature treatment, liquid-phase compaction of the obtained porous blanks with pitch, carbonization under pressure, and final heat treatment. Firing of the original workpieces is carried out in a heating mode in the temperature range of 400-900°C not more than 20°C/h. Intermediate high-temperature processing is carried out at 1750-2200°C and the heating mode of the workpieces in the range of 800-2200°C not more than 100°C/h and the content of the coke matrix in the workpieces based on the medium-temperature pitch at least 40%. Products are compacted with pitch containing no more than 40% α₁-fraction until porosity of no more than 10% is reached. The final heat treatment is carried out at a temperature not less than 50°C less than the temperature of intermediate high-temperature processing when heating the workpieces in the range of 800-1700°C no more than 100°C/h, and in the range 1700-2150°C - no more than 50 °C/h.

EFFECT: invention improves physical and mechanical characteristics of CCCM, prevents structural changes in the reinforcing component at the finishing stages of manufacturing, leading to decreased strength properties of the material.

1 cl, 1 tbl

Description

Technology area

The invention relates to the field of mechanical engineering, in particular to the production of carbon-carbon composite materials (CCCM), which can be used, for example, for assembling heavily loaded friction units under conditions of high energy loading and an oxidizing environment.

Various methods are known for producing carbon-carbon composite materials. So, for example, there is a known method of producing a friction composite carbon-carbon material reinforced with carbon fiber by impregnating a fibrous frame with pitch with further carbonization of the workpiece under pressure (patent RU 2510387 C1, Russia, publ. 2014). The disadvantage of this method is the presence of an additional stage of carbon fiber graphitization, which is expensive and laborious and associated with environmental hazards for personnel and the environment.

The closest prototype to the claimed one is a method for manufacturing CCCM, which includes the manufacture of a blank based on carbonized fibers and pitch binders, its carbonization in an inert atmosphere and compaction of the original composition with carbon from the vapor phase to the required material density (patent US 20170190629 A1, USA, publ. 2017 g.). However, this method multiplies the production cycle, which determines the high cost of products.

The strength characteristics of the friction fibrous composite material largely depend on the microdefects of its structure.

In the case of using carbonized fiber, as a result of the finishing high-temperature treatment of CCCM, the fiber shrinks due to a change in its structure. At the same time, at temperatures above 1750 ° C, after shrinkage, expansion of the matrix coke is observed, due to a certain thermal effect ["Carbon, interlayer compounds and composites based on it", Fialkov A.S.]. This contributes to the formation of significant microdefects in the structure of the composite material in its entire volume, which, in turn, lead to a decrease in the strength characteristics of the finished product and adversely affect the frictional and wear characteristics of CCCM.

The technical result of the proposed invention is a method for producing a composite material based on carbonized fiber and pitch matrix with increased physical and mechanical characteristics by creating special conditions in the technological modes of the manufacturing process, preventing structural changes in the reinforcing component at the finishing stages of manufacturing, which can lead to deterioration of operational properties.

The technical result in the proposed invention is achieved due to the fact that:

1. Firing of initial blanks formed on the basis of carbonized carbon fibers with a processing temperature of at least 1400 ° C and medium-temperature pitch with a softening temperature of 65-95 ° C is carried out at heating modes in the temperature range of 400-900 ° C no more than 20 ° C / hour , which contributes to uniform shrinkage of the primary matrix based on medium-temperature pitch with an α ₁ -fraction content of no more than 12%. An increase in the rate of temperature rise in this range can lead to significant local stresses in the bulk of the material and, as a consequence, a high degree of defectiveness of the microstructure of the product (table).

2. When the content in the blanks of the coke matrix based on the medium-temperature pitch is not less than 40%, the intermediate high-temperature treatment is carried out at a temperature of 1750-2200 ° C when the blanks are heated in the temperature range 800-2200 ° C no more than 100 ° C / hour, during which directional shrinkage of the reinforcing components is carried out. This stage ensures the thermal stability of the composite and guarantees the absence of permanent deformation of the fiber as a result of reheating at a given temperature. When the process is carried out at a rate of temperature rise in the specified range of more than 100 ° C / hour, the expansion of the coke matrix due to thermal action ["Carbon, interlayer compounds and composites based on it", Fialkov A.S.] will occur abruptly and intensively, which will lead to a high degree of defectiveness of the material due to the created stresses in the volume of the product (table).

3. Further liquid-phase compaction of billets with a porosity of at least 25% pitch with an α ₁ -fraction content of no more than 40% is carried out in carbonization processes under pressure at a maximum pressure of at least 20 MPa until the required porosity is reached no more than 10%, which contributes to the elimination of the resulting shrinkage of reinforcing components and structural changes in the coke matrix of material defects. Achievement of material porosity of more than 10% negatively affects the strength characteristics of the product (table).

4. The final heat treatment of the material is carried out at a temperature not less than 50 ° C less than the temperature of intermediate high-temperature processing when heating the workpieces in the temperature range 800-1700 ° C no more than 100 ° C / hour, and in the range 1700-2150 ° C - not more than 50 ° С / hour to ensure uniform shrinkage and expansion of the coke matrix in these temperature ranges. An increase in the heating rate in the indicated temperature ranges will lead to significant microdefects in the structure of the finished product and a decrease in the strength characteristics of CCCM. When this operation is carried out at temperatures above 2150 ° C, structural changes in the reinforcing components will be observed, which also lead to a decrease in the strength characteristics of the material (table).

Table. Comparative characteristics of different options for friction carbon-carbon products

Variants Average value of bending strength, MPa Average compressive strength, MPA Average value of interlayer shear, MPa 1. CCCM at intermediate high-temperature treatment at a temperature of 1750-2200 ° C (according to the proposed method) 185.36 223.31 30-33 2. CCCM with coke matrix content based on medium-temperature pitch less than 40% 161.19 203.07 20-26 3. CCCM during firing at a rate of temperature rise in the range of 400-900 ° C more than 20 ° C / hour 173.06 144.58 21-24 4. CCCM at intermediate high-temperature treatment with a temperature rise rate in the range of 800-2200 ° С more than 100 ° С / hour 142.47 132.82 14-17 5. CCCM with a porosity content of more than 10% 142.43 155.17 16-18 6. CCCM at finishing heat treatment with temperature rise rates in the ranges 800-1700 ° C and 1700-2150 ° C over 100 ° C / hour and 50 ° C / hour, respectively 108.71 112.93 7-10 7. CCCM with intermediate high-temperature treatment at a temperature <1750 ° С 130.25 151.10 10-15 8. UKM with intermediate high-temperature treatment at temperatures> 2200 ° С 182.52 174.24 18-22 9. CCCM without intermediate high-temperature treatment 115.68 132.72 10-15 10. CCCM at finishing high-temperature
processing> 2150 ° C 135.98 147.50 15-18

Claims (2)

1. A method of obtaining a carbon-carbon composite material by firing the initial molded workpieces based on carbon fibers and pitch binders, subsequent intermediate high-temperature treatment, liquid-phase compaction of the obtained porous workpieces with pitch, subsequent carbonization under pressure and final heat treatment, characterized in that the initial workpieces are fired in the heating mode in the temperature range of 400-900 ° C no more than 20 ° C / h, intermediate high-temperature processing is carried out at a temperature of 1750-2200 ° C when heating the workpieces in the temperature range 800-2200 ° C no more than 100 ° C / h and when the content in the blanks of the coke matrix based on the medium-temperature pitch is not less than 40%, after which the products are compacted with pitch with the content of α ₁ -fraction no more than 40% until the porosity is no more than 10%, while the final heat treatment of the blanks is carried out at a temperature of no less than 50 ° C less than the intermediate high-temperature temperature processing in the heating mode of workpieces in the temperature range 800-1700 ° C no more than 100 ° C / h, and in the range 1700-2150 ° C - no more than 50 ° C / h. 2. The method according to claim 1, characterized in that at the stage of forming the initial blanks, pitch binders are used with an α ₁ -fraction content of not more than 12% with a softening temperature of 65 ° C to 95 ° C.