Cyclic stress–strain response of superelastic Cu–Al–Mn alloy single crystals

Stress–strain response of cyclic superelastic deformation was examined in Cu–20at.%Al–10at.%Mn shape memory alloy single crystals. As the superelastic deformation was repeated, the critical stress for the onset of stress-induced transformation decreased at an almost constant rate to zero by a finite number of cycles Nc. By further cycles residual martensite was accumulated until all the stress-induced martensite was left after unloading. The decrease of the stress per cycle and the number Nc depended on the direction of applied stress, i.e. tension, compression and tension–compression, and also the crystal orientation. These Nc’s can be related by a linear S–N curve; log Nc decreased linearly with increasing log Δσ, where Δσ is the hysteresis-width in superelastic stress–strain curve. The observed fatigue behaviour can be understood in terms of internal stress of dislocation substructure formed during the cycles.