The Ta-Si System: Reevaluation of the Liquid Compositions in the Invariant Reactions and Determination of the Invariant Reaction Involving Both βTa5Si3 and αTa5Si3 Phases

Transition metal silicides are of great interest as high-temperature structural materials. Recent investigations aimed at the development of high-temperature Niobium-base structural alloys where silicide phases play a major role. Tantalum, in spite of its high atomic mass, is a potential micro-alloying element in these alloys to provide higher strength at high temperatures. In this work the invariant reactions of the Ta-Si system were reviewed via microstructural characterization of as-cast alloys. Samples were prepared by arc melting and their microstructures were characterized by scanning electron microscopy and x-ray diffractometry. The results confirmed the solid phases and the nature of the invariant reactions in this system. Few corrections in the currently accepted phase diagram are suggested: (1) the composition of the liquid phase that participates in peritectic formation of Ta2Si should be near 32 at.% Si instead of 28 at.% Si; (2) the inclusion of the βTa5Si3 ↔ αTa5Si3 + L metatectic reaction involving the βTa5Si3, αTa5Si3 and L phases.