Hydrogen-induced Surface Damage of NiTi Shape Memory Alloy

The phase transformation and damage at the surface of near-equiatomic NiTi shape memory alloy were investigated.The results show that similar to ustenitic stainless steel the generation of crack on the surface of NiTi alloy during the aging at room temperature after hydrogen electro-charging is related to the surface stress produced from the hydrogen release and the reducing of hydrogen induced martensite.The growth of crack lasted for more than 5 days.The morphology of stress-induced martensite and hydrogen-induced martensite is similar and could not be distinguished.The interface between hydride and base alloy and the interface between hydrogen-induced martensite and the austenite alloy could be the crack source.