Green Body Defect Control and High Temperature Mechanical Properties of Gel-Casting/Reactive Melt Infiltration SiC Based Parts

To solve the problem of macro-crack and residual silicon content of SiC ceramic parts caused by the carbon black agglomeration and insufficient content, an effective method to control the micro-structure defect and residual silicon content and to improve the mechanical properties of SiC ceramic parts at high temperature was proposed. Short carbon fibers (CF) serve as the carbon source, the dispersibilities of carbon black and short carbon fiber in ceramic slurry were comparatively investigated and the influences of the two carbon sources on the quality of the green body were analyzed. The micro-structure and phase composition of the reaction infiltrated Cf/SiC ceramic were observed by SEM and XRD. The effects of carbon fiber content on high temperature bending strength and fracture toughness of the SiC ceramic were discussed. The results show that short carbon fibers better disperse in ceramic slurry, and large-size pores and cracks in the ceramic green body can be well controlled. When in the reactive melt infiltration process, the porous structure formed by carbon fiber and ceramic particles facilitate the infiltration of liquid silicon, and the carbon fiber dissolves in the silicon liquid and reacted form β-SiC surrounding the carbon fiber surface. As the volume fraction of short carbon fiber increases (0 to 40%), the residual silicon content in the ceramic matrix decreases, and the high temperature (1 350 ℃) performance of the ceramic part increases firstly then decreases. When the short carbon fiber volume fraction gets 20%, the high-temperature flexural strength and fracture toughness reach the highest, 343±19 MPa and 5.04±0.27 MPa•m1/2 respectively. © 2019, Editorial Office of Journal of Xi'an Jiaotong University. All right reserved.