Physical nature of martensite transformations in B2-type Ti compounds and TiNi-based alloys

Thermoelastic martensite transformations in alloys based on titanium nickelide are a complex hierarchical process occurring at different structural scale levels. The feasibility and temperature of these transformations are determined in many respects by peculiarities of the electronic structure of TiNi-based alloys. In the review, we analyze the nature of structural instability of the high-temperature B2-phase in TiNi-based alloys and B2-type Ti intermetallic compounds with resort to data of our experimental electronic structure research and energy-band structure calculations. It is shown that the concept of martensite transformations in TiMe intermetallic compounds as having their origin in tendency of titanium to polymorphic transformation in the lattice of the compounds makes it possible to formulate criteria to control the temperature of martensite transformations. Electronic peculiarities responsible for precursor effects in the alloys are analyzed.