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Abstract

Titanium-Tantalum based alloys have recently become of interest as novel high temperature shape memory alloys (HTSMA) since these materials exhibit a martensitic transformation with a transformation temperature well above 350 K.

In our study we use density-functional theory (DFT) to study the stability and transformation between competing phases in Ti-Ta: the high temperature austenite beta phase, the low temperature martensite alpha'' phase and the detrimental omega phase.

The chemical disorder in Ti-Ta solid solutions is modelled by special quasirandom structures. To obtain the minimum energy path along the transformation between the phases as a function of composition we use the solid-state nudged elastic band method. Our results reveal a strong correlation between the change in relative stability of the martensite and austenite phase at T=0K and the transformation temperature. Furthermore, the predicted stability ranges of the involved phases are in good agreement with experimental findings. For an analysis at finite temperature we take into account vibrational and electronic contributions to the free energy.