A systematic investigation on the role of microstructure on phase transformation behavior in Ni-Ti-Fe shape memory alloys

A systematic study on the phase transformation behavior in a polycrystalline Ni-Ti-Fe shape memory alloy is reported. The investigation was carried out through series of differential scanning calorimetry (DSC) tests on three different samples with distinctly different microstructures of the alloy processed through different thermo-mechanical routes. The applied procedures involved cold rolling and marforming (rolling in liquid nitrogen) followed by short annealing treatments to recover the cold worked microstructure. These treatments altered the microstructure in terms of grain size, misorientation (defects) and texture. Three different microstructures were generated through adopted deformation processes (i) lower degree of texture, (ii) textured and (iii) refined grains with texture. The influence of the microstructural parameters on the phase transformations in terms of transformation temperature (TT) and associated energy of absorption/release was investigated. Temperature of transformation (TT) between different samples was affected predominantly by the grain size difference while enthalpy of transformation (austenite ↔ martensite) was mainly due to differences in texture, stored energy and in-grain misorientation. Though the differences in TT and enthalpy were not very significant, these results form a guideline for microstructure tailoring of bulk scale manufacturing of these alloys.