Enhanced Fatigue Resistance of Nanocrystalline Ni50.8Ti49.2 Wires by Mechanical Training

In this paper, the fatigue resistance of superelastic NiTi shape memory alloy (SMA) wires was improved by combining mechanical training and nanocrystallization. Fatigue tests were performed after with a peak stress 600 MPa for 60 cycles nanocrystalline (NC) wires, associated microscopic mechanism investigated using transmission electron microscopy (TEM) Kikuchi diffraction (TKD). The results showed that stress-controlled effectively functional stability (the accumulated residual strain decreased 83.8% in first 5000 cycles) NC SMA as well increased average structural life 187.4% (from 4538 to 13,040 cycles). TEM observations TKD revealed training-induced dislocations resulted lattice rotation preferential grain orientation. finite element method (FEM) simulation indicated orientation tended decrease local concentration energy density. Combined fractography analysis, uniform deformation caused changed crack growth mode from multi-regional propagation single-regional propagation, improving life.