Fabrication of Ceramic-Ceramic Composites by Chemical Vapor Deposition

摘要

Toughened ceramic composites were produced by the simultaneous chemical vapor deposition of two phases. Fracture toughness values were nearly double the value of SiC when CH sub 3 SiCl sub 3 and TiCl sub 4 vapors were used to produce SiC-TiSi sub 2 composites. Other systems consisting of SiC and the metal or metal carbides of Ni, Cr, W, and Mo were examined. Equilibrium thermodynamic analyses of these systems were performed as a function of the chemical vapor deposition variables: temperature, total pressure, and reactant concentration. These calculations confirmed that the volatile species used early in this work (organometallic compounds of Ni and Cr and the fluorides of W and Mo) were not suitable for the production of toughened composites. Additional work is under way to produce composites from the oxychlorides or carbonyls of Ni and Cr or the chlorides or oxychlorides of W and Mo. Thermodynamic calculations also indicated that SiC and TiC should be codeposited when CH sub 3 SiCl sub 3 , TiCl sub 4 , and a hydrocarbon are used as the coating gases. Much additional work remains to produce SiC-TiC composites and to control the morphology of the TiSi sub 2 dispersed phase so that optimum fracture toughness values can be obtained. (ERA citation 09:050173)