Computational thermodynamics and kinetics of displacive transformations in titanium-based alloys

The thermodynamics of Ti-based systems are described for β-α′/α″ martensitic transformation and athermal ω formation at low temperatures. The new descriptions can better represent the relationship between the partitionless equilibrium temperature and the measured martensite-formation/reversion temperatures. The anomalous β-stabilizing effects of Al, Sn, and Zr in ternary Ti-V/Nb-based alloys are well modeled for the first time. The Gibbs energy function of ω-Ti at ambient pressure is assessed. The formation temperature of athermal ω phase is assessed in some binary systems and estimated in some ternary systems based on electrical resistivity and first-principles calculations. The critical driving force for heterogeneous martensitic nucleation is modeled by solution-hardening interfacial friction using the present thermodynamic descriptions. The competition between martensite and athermal ω phase can be understood based on their transformation thermodynamic and kinetic factors.