Ageing effects in a Cu-Al-Ni shape memory alloy

Abstract
Ageing of a Cu-l4.3Al-4.1Ni (wt.%) shape memory alloy was investigated by resistometry and scanning electron microscopy. Four stages were distinguished in isochronal annealing experiments. Underlying processes were discussed with respect to the changes observed in the particular stages. In the early stages of ageing, annealing of quenched-in vacancies is probably the dominant process ; the effect of ordering processes seems to be negligible. A decrease in the hysteresis width precedes a pronounced γ₂ phase precipitation, which takes place at temperatures above 300 °C. Above 370 °C, the alloy ability of martensitic transformation is being lost.