Anisotropic Behaviour in Cu-Zn-Al SMA Due to the Oriented Growth of γ Precipitates

Abstract
The two way shape memory effect (TWSME) is usually induced by the presence of either stabilized thin plates of martensite or particular defects breaking the symmetry of the parent phase and making only one or a few variants favourable upon transformation. Generally, the defects are created in the material by performing a certain number of transformation cycles. An alternative method to induce the TWSME, avoiding the heavy training processes, has been obtained for Cu-Zn-Al single crystal . It consists on the introduction of small γ precipitates by apropriated thermal treatments. Then the precipitates are made to grow asymmetrically by the action of an applied stress. Anisotropic residual stresses then favour the appearance of some selected martensite variants at the transformation cycles.