Phase equilibria of low-Ni side in Nb–Ni–Ti system at 1100 °C

Abstract

The phase equilibria related to liquid phase in low-Ni side of Nb–Ni–Ti system at 1100 °C were investigated through scanning electron microscope (SEM), electron probe micro-analyzer (EPMA), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results show that there exists liquid phase in equilibrium with continuous solid solution (Nb, βTi) and compound TiNi in low-Ni side of Nb–Ni–Ti system at 1100 °C. The liquid phase region originates from low-Ni side of binary Ti–Ni system and extends to 9.4 at% Nb in isothermal section of Nb–Ni–Ti phase diagram. The solid solubility of Nb in binary compound TiNi is about 10.6 at%. At 1100 °C, there exist two three-phase regions consisting of liquid+(Nb, βTi)+TiNi and (Nb, βTi)+TiNi+XB in Nb–Ni–Ti system, where XB is the compound with hexagonal structure and composition of 32.8Nb–44.5Ni–22.7Ti. The wide two-phase region (Nb, βTi)+TiNi exists between these two three-phase regions. In this two-phase region, Ti content in continuous solid solution (Nb, βTi) varies from 6.6 at% to 25.7 at%, but Ni content is almost the same, which is about 4.0 at%. The eutectic transformation L↔(Nb, βTi)+TiNi takes place at about 1138 °C in Nb–Ni–Ti ternary system.