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

Abstract

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.