Study On Liquid Silicon Infiltration Process Of Molded C/SiC Material

Carbon fiber reinforced SiC ceramic matrix composites(Cf/SiC)have a series of advantages such as low density,high strength,high modulus,low coefficient of thermal expansion and excellent tribological properties,which is optimistic to use as structural and functional material.According to the length and weaving methods of carbon fiber,Carbon fiber reinforced composite material has a variety of reinforced structure.The short fiber.reinforced silicon carbide ceramic matrix composites have the characteristics of low cost and good uniformity,in additon,it has the potential of industrial production by using the process of liquid silicon infiltration(LSI).This study prepared Cf/SiC by LSI process and optimize the preparation technology to improve the property of the material such as material uniformity and density.The effect of content of a-SiC powder and resin on the property of material is also been systematically studied.Other than that,the study propose the SiC grain growth theory in liquid silicon infiltration through the observation and the analysis of corroded surface of Cf/SiC composites.Cf/SiC composites were prepared by LSI process.Due to Cf/SiC composites has the continuous and smooth C/C interface,it is convenient to observe the C/SiC interface after the interface been corroded by mixed solution of K3Fe(CN)6 and KOH.We conclude that SiC are produced by two different growth theory:silicon atoms diffuse into carbon through the vacancy mechanism which lead to the appearance of amorphous SiC.As heat-retaining time increasing,amorphous SiC gradually transform into the crystalline state.Carbon atoms diffuse in the SiC layer and dissolve in the liquid silicon by forming Si-C group.Coarse silicon carbide crystals are formed by the dissolution-precipitation mechanism,which accompany the emergence of stacking fault.The related properties of Cf/SiC composites were improved through the improvement of a series of preparation process.The addition of silicon carbide powder in phenolic resin can reduce the porosity of C/SiC body,the flexural strength of the material were improved effectively.When the vacuum degree is low,the C/SiC body is placed on the C/C support to solve the problem of low density of the material after liquid silicon infiltration process.When short carbon fiber was treated by ultrasonic dispersion,the uniformity of Cf/SiC composites were improved obviously and the flexural strength of the material increase evidently.The relationship between the content of raw materials and the mechanical properties of Cf/SiC composites was studied.The results of the analysis show that the flexural strength of the material increases first and then decreases with the raising of the content of short carbon fiber.While the volume content of short carbon fiber is 29%,the flexural strength of the composites is the highest.The flexural strength of the material improve first and then decline with the raising of the content of resin.While the volume content of resin is 37%,the composites has the highest flexural strength.