Fracture properties of polycrystalline NiTi shape memory alloy

Fracture properties of polycrystalline NiTi shape memory alloy have been investigated with the tension experiments on smooth and notch samples at different temperatures. The dog-bone tension tests demonstrate that above room temperature, NiTi with superelasticity effect presents enhancive ductility with the increase of temperature. Above the ceasing temperature of stress-induced martensite Md, EBSD investigation on crack indicates that the crack tends to propagate along the easy cleavage plane of {110} or {100}. If the apparent fracture toughness is larger than the critical stress intensity factor for expansion of martensite, the crack tip can be trapped by continual expansion of martensite, and the samples fracture in a ductile way. Otherwise, the crack tip could not be trapped by martensite expansion, the martensite transformation reduces the fracture toughness of NiTi, and the samples fracture in a quasi-brittle way.