Effect of titanium alloying on the structure, the phase composition, and the thermoelastic martensitic transformations in ternary Ni–Mn–Ti alloys

The behavior and the properties of Ni$_{50}$Mn$_{50-y}$Ti$_y$ ($y$ = 5, 10, 15, 25, 30) alloys are studied by electrical resistivity measurements, transmission electron microscopy, scanning electron microscopy, and X-ray diffraction over a wide temperature range. It is found that the martensite transformation temperature of the complex alloys can be significantly lower than the transformation temperature range of binary Ni$_{50}$Mn$_{50}$ and Ni$_{49}$Mn$_{51}$ alloys. Apart from tetragonal $L1_0$ martensite, a complex multilayer (10M) crystal lattice is revealed in the alloys. Martensite is shown to have a predominant morphology in the form of hierarchic packets of thin coherent plates of nanoand submicrocrystalline crystallites, which have plane habit boundaries. In the case of tetragonal $L1_0$ and 10M martensite, these boundaries are close to $\{011\}_{B2}$ and are pairwise twinned along one of the 24 equivalent $\{011\}\langle10\bar{1}\rangle_{B2}$ twinning shear systems.