•The thermodynamics of low-temperature displacive transformations in Ti-based systems are described.•The anomalous β-stabilizing effects of Al, Sn, and Zr are correctly modeled for the first time in Ti–V/Nb-based systems.•The critical driving force of martensitic nucleation in Ti-based alloy is modeled by solution-hardening interfacial friction.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.

•A molar volume database for Ti-base solid solutions is established.•Bcc, hcp, and martensitic orthorhombic phasesare included in the database.•A density criterion is used to predict whether martensite is hcp or orthorhombic.The room-temperature molar volumes of bcc (β), hcp (equilibrium α or martensitic α′), and orthorhombic (martensitic α′′) phases are modeled for a number of Ti-base solid solutions in the CALPHAD framework. The martensitic molar volume is continuous at the α′/α′′ transition composition. Hcp and orthorhombic structures are modeled separately, and the predicted martensitic structure is taken as the denser one.

Best known as co-author of the historic 1953 Invariant-Plane Strain (IPS) theory of martensite, Professor David S. Lieberman pioneered the crystal kinematic foundation of the theory of martensitic transformations. An early proponent of the practical potential of thermoelastic alloys, his interdisciplinary studies of a broad range of martensitic systems established mechanistic principles of point defect interactions underlying important mechanical behaviors, while his creative interests spanned diverse areas including materials sustainability and technical education reform. His special mix of strong will and singular humor played a unique role in shaping the martensite tradition.