Effect of Nb Addition on the Thermodynamic of Solidification in a Ti-Ni-Cu Alloy

The solidification process of Ti_52-xNi₃₈Cu₁₀Nb_x alloys was evaluated using the CALPHAD method and microstructural analyses of as-cast alloys with Nb additions of x = 4, 6, 8 and 10 at%. Both in Scheil calculator and structural analyses, the observed phases were TiNi, β-Nb/Ti, and Ti₂Ni. TiNi is the matrix phase, and it presented similar amounts of Ti and Ni with varying Nb contents. Enrichments of Ti content and depletion of Ni are expected in the liquid with the solidification of this phase. Formation of Ti₂Ni and β-Ti is related to the excess of Ti. Increasing Nb content hinders the formation of Ti₂Ni, favoring β-Ti. In turn, Ni depletion and Nb accumulation led to the TiNi/β-Nb eutectic. In the intermetallic phases, coherent ratios were obtained when Cu was considered a substitute for Ni, and Nb, for Ti.

Keywords:
TiNiCu-based alloys; shape memory alloy; solidification; Scheil calculator