THE 2-WAY SHAPE-MEMORY EFFECT IN CU-ZN-AL SINGLE-CRYSTALS - ROLE OF DISLOCATIONS AND STABILIZATION

The two way shape memory effect (TWME) has been studied in single crys tals of Cu-Zn-Al alloys in which dislocations have been introduced by plastic deformation of the martensite. The influence of the dislocatio ns manifests itself in the formation of thin martensite plates above t he bulk M(S) in order to reduce the stress fields, and in the selectio n of preferentially one group of self accommodating variants with only a small TWME. A perfect TWME can be obtained after stabilization of a single stress induced variant. This is due to the retention of small martensite nuclei which are stable to quite high temperatures, which c an grow on cooling without the need to be nucleated first, and which c an impede the growth of other inclined variants. The present results a re compared with fatigue cycling experiments in single crystals and th e TWME in trained polycrystals.