Diffusion kinetics of the carburization and silicidation of Ti3SiC2

The ternary carbide Ti3SiC2 possesses a unique set of properties that could render it a material of considerable technological impact. The motivation for this work was to enhance the hardness and oxidation resistance of Ti3SiC2 by altering its surface chemistry. Reaction of Ti3SiC2 with single crystal Si wafers in the 1200-1350 degrees C temperature range resulted in the formation of a dense surface layer composed of a two phase mixture of TiSi2 and SiC. This layer grows in two distinct morphologies; an outer layer with fine (1-5 mu m) SiC particles and an inner coarser (10-15 mu m) one. The overall growth rates of the layers were parabolic. Comparison with previously published results supports the conclusion that diffusion of Si through TiSi2 is rate limiting. In the 1400-1600 degrees C temperature range, reaction of Ti3SiC2 with graphite foils resulted in the formation of a 15 vol. % porous surface layer of TIG, (where x>0.8). It is shown that the carburization kinetics are rate limited by the diffusion of C through TiCx,. Both carburization and silicidation increased surface hardness, the latter also enhanced the oxidation resistance by about three orders of magnitude. (C) 1998 American Institute of Physics.