Sintering And Mechanical Properties Of Carbon/carbon Composites

The carbon/carbon composite material is a high-performance composite material with carbon as matrix and reinforced by carbon fibers.Therefore,it combines the excellent mechanical properties of the carbon fiber composite material with the inherent high-temperature resistance of the carbon material.Since the beginning of the 21st century,with the rapid development of carbon/carbon composite materials in the aerospace,military,marine ship and civil fields,the requirements and expectations for the safety,reliability,and economics of composite materials have also increased.The development of a short process and low-cost preparation process has important engineering significance for the promotion and application of carbon/carbon composite materials.In this paper,sintering preforms were prepared by the composite method of fiber impregnation using natural flake graphite as matrix,domestic T300 carbon fiber as reinforcement and mesophase pitch powder as impregnant.Then,the preforms were sintered by two stages of hot press sintering and pressureless sintering,respectively,so as to obtain a pitch-based carbon/carbon composite material with excellent mechanical properties,relatively high density,and good dimensional stability.Compared with the traditional technology,this process has the advantages of short flow,low requirement for production equipment,high production efficiency,and easy mass production.Therefore,it has the purpose of shortening the preparation cycle and reducing the cost,and has important industrial application value.At the same time,the effects of the raw material mass ratio?P/G?,impregnation temperature,impregnation pressure,and sintering temperature on the mechanical properties and microstructure of the composites in the two sintering processes were studied,through a series of experimental research and analysis,the main research results are obtained as following:For hot press sintering process,when the P/G is 1,the impregnation temperature is300°C,and the sintering temperature is 1400°C,the mesophase pitch can be fully impregnated between the matrix and the carbon fiber and carbon fiber bundles,and the flow densification effect is optimal.The actual density of the carbon/carbon composites reached 1.755g·cm^-3,the apparent porosity was only 1.69%,the densification was 95%,and the fracture toughness and fracture work were 6.02MPa·m^1/2 and 0.92kJ·m^-2respectively.At the same time,the flexural strength of the carbon/carbon composites obtained was 363±20MPa,and the maximum flexural strength was as high as 383MPa,and the flexural strength has reached the advanced level reported at home and abroad.For the pressureless sintering process,when the P/G is 1,the impregnation temperature is 500°C,the impregnation pressure is 10MPa,and the final sintering temperature is 1400°C,the prepared carbon/carbon composites have the best mechanical properties and densification.The flexural strength of the composite can reach283±15MPa,the actual density is 1.663g·cm-3,the apparent porosity is 3.55%,the density can reach 90%,and the fracture performance is also relatively high.Compared with the hot press sintering,the mechanical properties of carbon/carbon composite products prepared by the pressureless sintering process are reduced,and the densification effect is also relatively weakened,but it also basically meets the use requirements under general conditions.And because the high-temperature pressureless sintering process has simpler production conditions,lower production equipment requirements,higher production efficiency,and can achieve mass production,the process has great industrial significance.