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

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 (1 1 1) parallel to drawn direction texture. The reduction of fatigue striation spacing revealed training-induced plastic deformation and enhanced (1 1 1) texture contributed to hindering crack propagation.

Automated summary

The structural fatigue life of nanocrystalline NiTi wires was improved by stress-controlled mechanical training, with the improvement increasing with grain size. The untrained samples showed a decrease in structural fatigue life with increased grain size. However, after training, the structural fatigue life increased with grain size due to the generation and movement of dislocations during training, which improved the orientation intensity of (1 1 1) texture parallel to the drawn direction. The reduction of fatigue striation spacing indicated training-induced plastic deformation and the enhanced (1 1 1) texture hindered crack propagation.