On the mechanical behavior of single crystal NiTi shape memory alloys and related polycrystalline phenomenon

Room temperature monotonic and cyclic stress–strain curves for single crystal and polycrystalline NiTi shape memory alloys containing Ti3Ni4 precipitates are presented. The tensile and compressive single crystal results illustrate the importance of crystallographic texture, the unidirectional nature of the martensitic transformation, and martensite detwinning on tension-compression stress–strain asymmetry in polycrystalline NiTi. Moreover, results on the fatigue of NiTi single crystals demonstrate the fundamental characteristics of cyclic deformation in NiTi alloys and the importance of texture on the fatigue of polycrystalline NiTi.