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 °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 °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 °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.