Investigation of phase equilibria in the Ti-Al-Si-Nb system at low Nb contents Original Research Article

Phase equilibria in the α/α2 phase region of the Ti-Al-Si-Nb system at Nb content 2.5, 3.5 and 5 at.% were studied in alloys as-cast and heat-treated at 800 °C. Samples were prepared by arc-melting technique, homogenized at 1350 °C and then heat-treated at 800 °C, followed by ice water cooling. The structure of the alloys was characterized by means of X-Ray diffraction, differential thermal analysis, electron probe microanalysis, scanning electron microscopy and transmission electron microscopy. The continuous solid solutions with variable compositions (Ti1−x,Nbx)3(Si1−y,Aly) (η) (0.05≤x≤0.07, 10−3≤y≤0.02) was detected at 800 °C for the first time in the multi-component alloys based upon the Ti-Si system. It was stabilized by Nb additions in the alloys with low Al content. A peritectoid reaction β+α→η was observed. Additions of Al neutralized the stabilizing effect of Nb resulting in an α + Ti5Si3 (z) equilibrium.