Micromechanism of Propagation of Fatigue Cracks in Pseudoelastic NiTi Shape-Memory Alloy

We analyze the kinetic features and micromechanism of propagation of fatigue cracks in pseudoelastic nitinol alloy with shape-memory effect under the conditions of constant-amplitude cyclic loading with stress ratios R = 0.2 and 0.5. It is established that, independently of the parameter R, fatigue cracks grow by the quasicleavage mechanism, which is explained by the austenite-martensite deformation transformation at the crack tip. This also explains the fact that the maximal value of the stress intensity factor in a loading cycle (but not its range) is responsible for the kinetics of fracture observed as the stress ratio R changes.