Enhanced Functional Fatigue Resistance of Cu-Al-Mn Superelastic Wire Bamboo-Like Grain Structure

Abstract

The enhanced fatigue resistance of superelastic Cu-Al-Mn shape memory wires was investigated via a bamboo-like grain structure obtained by cyclic heat treatment (CHT). Our findings reveal that increasing the number of CHT cycles facilitates grain growth, and the grain boundary will change from a brittle triple junction to a stronger straight grain boundary. This structural feature of grain boundaries alleviates stress concentration effects on dislocation motion. In particular, the 5CHT and 7CHT samples displayed negligible residual strain after unloading, following exposure to cumulative strains ranging from 2% to 10%, thereby showcasing superior superelasticity. From the functional fatigue test, the fatigue life of the shape memory wire subjected to 5CHT cycles exceeds 4650 cycles at 5% strain, which is more than five times that of the traditional polycrystalline quenched sample.