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Abstract

Ti-Ta-based alloys exhibit a high-temperature shape memory effect (SME) due to a martensitic transformation between an orthorhombic phase ( α ) and a body-centered cubic phase ( β ). The stability of the SME in binary Ti-Ta is compromised by the formation of detrimental phase ( ω ). It has been observed experimentally that alloying a third component to pure Ti-Ta hinders the formation of the ω phase. Both the stability of the SME and the transformation temperature depend strongly on the chemical composition; the underlying mechanism is, however, not fully understood. In this contribution, the stability and the transformation temperature are analyzed systematically as a func-tion of composition of Ti-Ta-X by means of calculations; in particular, it is examined how different elements and different concentrations affect the formation energy of the α , β and ω phases. The trends in formation energies are found to be related to the electronic properties and the size of the alloying elements. Simpler models that describe the compositional dependence of the transformation temperature are derived from first principles data and allow us to gain chemical insight into the effect of alloying on the relative phase stability. Our model is exploited to guide the experimental design of new stable and high-temperature shape memory alloys.