Phase equilibria in the Ti-rich corner of the Ti-Si-Ga system

Phase relations in the ternary Ti-Si-Ga system have been established experi mentally by means of a study of alloy samples in the as-cast condition and annealed at 1350 degrees C. The alloys were prepared by are melting. The in vestigation was carried out using physico chemical methods of analyses (met allography, X-ray powder diffraction, differential thermal analysis, and el ectron probe microanalysis over a limited composition range with samples co ntaining less than 38 at.% Ga and more than 62 at.% Ti. Liquidus and solidu s surface projections, the isothermal section at 1350 degrees C, and the is opleth at 68 at. % Ti are presented. Three surfaces of primary crystallizat ion of phases have been established: extended ones for Ti-5(Si,Ga)(3) and b eta (Ti-base solid solution) and a narrow one of Ti2Ga. The monovariant cur ves separating these are due to the eutectic reactions L <----> beta + Ti-5 (Si,Ga)(3) and L <----> beta + Ti2Ga and to the L + Ti-5(Si,Ga)(3) <----> T i2Ga peritectic reaction. The three-phase region (beta + Ti-5(Si,Ga)(3) + T i2Ga) results from the four-phase eutectic reaction L <----> beta + Ti-5(Si ,Ga)(3) + Ti2Ga. The composition of the ternary eutectic point E and the co mpositions of the coexisting solid phases have been determined. The solubil ities of Si in the gallides, and of Ga in Ti5Si3 and of both the elements i n Ti are given.