Training and two way memory effect in CuZnAl alloy

Abstract

The training and the resulting two way memory effect (TWME) of CuZnAl alloy have been systematically studied with a special torsion apparatus. Two kinds of training have been investigated: temperature cycling with a constant stress and stress cycling at a fixed temperature above A f. It has been shown that large (5–6% shear strain) and stable TWME can be obtained (several years at 50°C from annealing kinetics). The temperature cycling has been proved to be the most efficient; it involves low stresses and generates a low true plastic strain in the β phase, the high temperature shape is therefore very close to the initial one; the low temperature shape can be predetermined with a good accuracy by the application of a suitable stress. The temperature degradation of the TWME ocurs in two steps, the first one has been attributed to the training dislocations annealing (apparent activation energy 1.2 eV), the second one to the bainitic precipitation.