Phase Equilibria in the Ti-Rich Portion of the Ti-Ga-Sn System

Phase equilibria of the Ti-Ga-Sn system have been determined at primary crystallization and at 1000 °C in the composition interval ~ 50-100 at.% Ti based on differential thermal analysis, x-ray powder diffraction, scanning electron microscopy and electron microprobe analysis. Partial liquidus and solidus projections, the melting diagram, a number of vertical sections, isothermal section at 1000 °C, as well as the reaction scheme (Scheil diagram) for the Ti-Ga-Sn system were constructed. A ternary compound Ti₅GaSn₂ (τ) (Nb₅SiSn₂-type structure, tI32-I4/mcm), found by us previously, forms by peritectic reaction L + Ti₂(Sn, Ga) + Ti₅(Sn, Ga)_3-4 ⇄ τ at 1500 °C and has a wide homogeneity range from 9 to 23.5 at.% Ga at solidus temperature and from 4 to 34 at.% Ga at 1000 °C, and located along constant composition of ~ 62.5 at.% Ti. D8₈-type compounds Ti₅Sn₃ and Ti₅Ga₄ form a continuous solid solution, denoted Ti₅(Sn, Ga)_3-4, at all investigated temperatures. Ga-poor part of it (below ~ 12.5 at.% Ga) forms by an interstitial mechanism, while in the interval above ~ 12.5 at.% Ga it is a substitutional phase. Isostructural compounds Ti₂Sn and Ti₂Ga also form a continuous solid solution Ti₂(Sn, Ga) at solidus temperatures, which decomposes with decreasing temperature. Meanwhile, at 1000 °C, one more continuous solid solution Ti₃(Sn, Ga) forms between isostructural compounds Ti₃Sn and Ti₃Ga.