The role of hydride, martensite and atomic hydrogen in hydrogen-induced delayed fracture of TiNi alloy

The role of atomic hydrogen, hydrogen-induced martensite and hydride in hydrogen-induced delayed fracture of a TiNi shape memory alloy during charging under a sustained load has been investigated using a notched tensile specimen. The results show that hydrogen-induced delayed fracture of the TiNi alloy can occur, and the normalized threshold stress intensity factor, KIH/KIC, decrease linearly with the logarithm of the total hydrogen concentration CT, i.e., KIH/KIC=2.01−0.25 ln CT. The content of the hydrides increase gradually, and then the intrinsic fracture toughness of the hydrogenated specimen decrease sharply during dynamic charging. The formation of hydrides is the main reason of hydrogen-induced delayed fracture of the TiNi alloy. The role of atomic hydrogen and hydrogen-induced martensite in hydrogen-induced delayed fracture is very small.