Combined effects of grain size and training on fatigue resistance of nanocrystalline NiTi shape memory alloy wires

Abstract

The structural fatigue life of nanocrystalline NiTi wires with grain size ranging from 53 nm to 125 nm was improved by stress-controlled mechanical training and the percentage of the improvement increased with grain size. The structural fatigue life decreased with the increased grain size for the untrained samples. After training, the structural fatigue life increased with grain size. The generation and movement of dislocations during training contributed to lattice rotation, improving orientation intensity of 〈111〉 parallel to drawn direction texture. The reduction of fatigue striation spacing revealed training-induced plastic deformation and enhanced 〈111〉 texture contributed to hindering crack propagation.