On the Origin of the Two Way Shape Memory Effect in Cu-Zn-Al Alloys

Abstract
Several training procedures have been found suitable to induce the two way shape memory effect (TWSME) in copper based alloys. Complex dislocation arrangements can be produced by transformation cycling, which are believed to be the cause of the TWSME. Small martensite plates can be stabilized, serving as origin of subsequent transformations, or deformation around second phase precipitates are used. In this work, the role of the dislocations arrangements is investigated. It is shown that the stress field around the dislocations leads to the formation, in the β phase, above the Ms, of small martensite plates. These martensites do not necessarily correspond to the trained variant. Complex defects consisting of dislocations and heavily deformed martensites are thus produced. The role of these complex defects on the TWSME is discussed and possible mechanisms are suggested.