Theoretical analysis of transformation temperatures of TiTa-based high temperature shape memory alloys

Ti–Ta-based high-temperature shape memory alloys (HTSMAs) are of interest due to their high transformation temperatures, good mechanical strength, corrosion resistance, and biocompatibility. This work predicted the transformation behaviour of Ti–Ta alloys using fundamental parameters including the number of valence electrons per atom (e v /a), valence electron concentration (VER), and atomic size factor. For binary Ti–Ta alloys with 20–35 at% Ta, e v /a varies from 4.2 to 4.35 and VER from 0.1304 to 0.1091. The transformation temperatures decrease linearly with increasing e v /a and with increasing atomic size factor, but decrease linearly with decreasing VER. A binary Ti₇₀Ta₃₀ alloy was synthesised via vacuum arc remelting and homogenised at 1000 °C for 6 h. Differential Scanning Calorimetry (DSC) analysis revealed that the alloy’s transformation temperatures are within 5% of the theoretically predicted values. In ternary Ti–Ta–X systems, a saturation behaviour of transformation temperatures is observed when e v /a exceeds ~ 4.35 and VER approaches ~ 0.1125, which is attributed to electronic structure stabilisation and solute-induced lattice strain. These findings show a predictive framework for estimating transformation behaviour in Ti–Ta-based HTSMAs based on fundamental alloy parameters.