Phase relations in the Al-rich corner of the Ti–Ni–Al system

Abstract Phase relations in the Al-rich corner of the Ti–Ni–Al system were determined for three partial isothermal sections at 900, 800 and 600°C by diffusion couples and 14 bulk alloy samples employing X-ray powder diffraction, optical microscopy and electron probe microanalysis (EPMA). The equilibrium diagrams are dominated by the ternary compound τ 1 with AuCu 3 -type. In some samples, annealed at 600 and 800°C, a (non-equilibrium) Ti 5 Al 11 phase with the ZrAl 3 -type was found, which formed during solidification followed by incomplete decomposition. A new metastable phase τ 5 was observed with a composition around Ti 13.8 Ni 20.1 Al 66.1 (at.%). On oxidation a quaternary phase Ti 3 NiAl 2 O 1− x with a filled Ti 2 Ni-type is formed. A Rietveld refinement of τ 1 with AuCu 3 -type is presented.