ANISOTROPIC BEHAVIOR IN CU-ZN-AL SMA DUE TO THE ORIENTED GROWTH OF GAMMA-PRECIPITATES

The two way shape memory effect (TWSME) is usually induced by the pres ence of either stabilized thin plates of martensite or particular defe cts breaking the symmetry of the parent phase and making only one or a few variants favourable upon transformation. Generally, the defects a re created in the material by performing a certain number of transform ation cycles. An alternative method to induce the TWSME, avoiding the heavy training processes, has been obtained for Cu-Zn-Al single crysta l. It consists on the introduction of small gamma precipitates by apro priated thermal treatments. Then the precipitates are made to grow asy mmetrically by the action of an applied stress. Anisotropic residual s tresses then favour the appearance of some selected martensite variant s at the transformation cycles.