R-phase transformation phenomena in thermomechanically loaded NiTi polycrystals

In situ neutron diffraction and ultrasonic experimental techniques have been used to investigate the B2 ↔ R transformation and R-phase reorientation processes occurring during thermal, mechanical and thermomechanical loading of NiTi shape memory alloy polycrystals. The effects of elastic and structural instabilities of the R-phase on the macroscopic thermomechanical σ–ε–T behaviors of NiTi polycrystals are discussed.