ON THE ORIGIN OF THE 2 WAY SHAPE-MEMORY EFFECT IN CU-ZN-AL ALLOYS

Several training procedures have been found suitable to induce the two way shape memory effect (TWSME) in copper based alloys. Complex dislo cation arrangements can be produced by transformation cycling which ar e believed to be the cause of the TWSME. Small martensite plates can b e stabilized, serving as origin of subsequent transformations, or defo rmation around second phase precipitates are used. In this work, the r ole of the dislocations arrangements is investigated. It is shown that the stress field around the dislocations reads to the formation in th e beta phase, above the Ms, of small martensite plates. These martensi tes do not necessarily correspond to the trained variant. Complex defe cts consisting of dislocations and heavily deformed martensites are th us produced. The role of these complex defects on the TWSME is discuss ed and possible mechanisms are suggested.