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Martensite

Acta Physica Polonica A

Ab initio calculations are used to predict tetragonal transformation of Co2Ti1-xFexAs Heusler alloys.We show that distortion of the cubic (austenite) Heusler structure induces a tetragonal (martensite) structure with space group I4/mmm.At tetragonality, with the c/a ratio of 1.30, 1.26, 1.22, 1.17, and 1.16 corresponding to x = 0, 0.25, 0.5, 0.75, and 1, respectively, the martensite phases become energetically more stable than the austenite ones.The negative values of tetragonal shear modulus parameter mean that the austenite phases of these alloys are elastically unstable, and consequently are expected to undergo martensitic transformations.The stability of the martensitic phases is confirmed by calculating the total spin polarized density of states at the Fermi level.The addition of Fe to the Co2TiAs alloy decreases the energy difference between the austenite and martensite phases, leading to a decrease of the martensitic transformation temperature TM .With TM higher than the room temperature for x = 0 and 0.25, these compounds are expected to behave like high-temperature shape memory alloys.

Martensitic Phase Transformations in Quaternary Heusler Alloys Co2Ti1-xFexAs