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 crystals of Cu-Zn-Al alloys in which dislocations have been introduced by plastic deformation of the martensite. The influence of the dislocations manifests itself in the formation of thin martensite plates above the bulk M(S) in order to reduce the stress fields, and in the selection 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 can grow on cooling without the need to be nucleated first, and which can impede the growth of other inclined variants. The present results are compared with fatigue cycling experiments in single crystals and the TWME in trained polycrystals.