Thermodynamic re-assessment and liquidus projection of the Cu–Ni–Ti system

Abstract

A critical thermodynamic re-assessment for the ternary Cu–Ni–Ti system was performed by means of the CALPHAD (CALculation of PHAse Diagram) approach, and a new set of self-consistent thermodynamic parameters for the Cu–Ni–Ti system was obtained. According to the reported crystal structures and homogeneity ranges, appropriate sublattice models were proposed for the τ4 and τ6 phases, which could achieve a better description than the previous stoichiometric compound model for phase compositions and primary phase regions. Three solid-state invariant reactions, CuTi + τ1 ↔ Cu4Ti3 + NiTi at 1074.86 K, Ni3Ti + NiTi + τ1 ↔ τ2 at 1074.39 K and NiTi + τ4 ↔ Ni3Ti + τ1 at 1175.11 K were predicted in the present work. Presently calculated liquidus projection eliminated the liquid miscibility gap of the Cu–Ni–Ti system on Cu–Ni side. Scheil reaction scheme of the entire composition range was also presented accordingly. Comparisons between the calculated results and the measured phase equilibria indicated that all the reliable experimental data were satisfactorily accounted for by the present modeling.