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Abstract

Shape memory alloys (SMAs) exhibit unique properties that are used in applications such as couplings, sensors or actuators in automobile industry, aviation and in other technological areas. To extend their range of applicability, it is of particular interest to develop SMAs that can be used at high temperatures (HTSMA), with a martensitic trans- formation temperature well above 373K. Promising results for a novel HTSMA have been found for the Ti-Ta system. Experimentally it has been observed that a large Ta concentration stabilizes the shape mem- ory effect due to suppressing the formation of the detrimental ω phase. But an increasing Ta content also leads to a reduction of the marten- sitic transformation temperature. In our study, we apply density functional theory (DFT) calculations to investigate the stability of the involved phases (α”, β, ω) as a function of the Ta concentration. To determine the mechanical and dynamical stability of the different phases, we calculate elastic constants and phonon spectra. Furthermore, the phonon density of states is used to include vibrational contributions to the free energy which allows us to compare the relative stability of the different phases as a function of temperature. Having characterized the stability of the different phases we investigate the energy profile along the transformation path.