SOLID-STATE INTERFACIAL REACTIONS OF TI3AL WITH SI3N4 AND SIC

Solid state interfacial reactions of Ti3Al with Si3N4 and SiC have been studied via both bulk and thin film diffusion couples at temperatures of 1000 and 1200-degrees-C. The nature of reactions of Ti3Al with Si3N4 and SiC was found to be similar. Only limited reactions were detected in samples reacted at 1000-degrees-C. In the Ti3Al/Si3N4, layered reaction products consisting of mainly titanium silicide(s), titanium-silicon-aluminide, and titanium-silicon-nitride were formed; in the Ti3Al/SiC, the reaction product was primarily titanium-silicon-carbide. In both cases, silicon was enriched near the surface region, and aluminum was depleted from the reacted region. Reactions at 1200-degrees-C resulted in a drastic change of the Si distribution profiles; the enrichment of Si in near surface regions was no longer observed, and the depletion of Al became more extensive. Titanium nitride and titanium-silicon-carbide were the major reaction products in the Ti3Al/Si3N4 and Ti3Al/SiC reactions, respectively. Mechanisms of driving the variation of Si, N, and C diffusion behavior (as a function of temperature) and the depletion of Al from the diffusion zone are suggested. It is proposed that reactions of Ti3Al with Si3N4 and SiC lead to in situ formation of a diffusion barrier, which limits the diffusion kinetics and further reaction. The thermodynamic driving force for the Ti3Al/Si3N4 reactions is discussed on the basis of Gibbs free energy.