ENHANCEMENT OF SHAPE-MEMORY AND ITS ANISO TROPY BY TRAINING TREATMENTIN AN FE-32MN-6SI ALLOY

The improvement of shape memory effect due to the austenite (gamma) re versible arrow epsilon (epsilon) martensitic transformations and the d evelopment of its anisotropy by training treatment were studied by usi ng an Fe-32Mn-6Si alloy. The training treatment of five times repetiti ons of 2% tensile deformation at 300K and heating up to 723K was given to the solution-treated samples. By this treatment, lots of stacking faults are introduced in the samples. The test specimens were cut from the trained plates either parallel (0 degrees sample) or vertical (90 degrees one) with respect to the training direction. In the 0 degrees samples the pre-existing stacking faults are found to be very effecti ve not only to produce the stress-induced epsilon martensite but also to increase the gamma strength against usual slip. A seemingly one thi ck epsilon plate has been revealed to consist of nano-scale gamma/epsi lon lamellar structure which is preferable to hold the back stress. Th e shape recovery improved due to the reversible motion of Shockley is partial dislocations assisted by this back stress. The recovery stress for backward motion of Shockley partial dislocations during the epsil on-->gamma reversion is found to increase markedly by the training tre atment. On the other hand. in the 90 degrees samples, the pre-existing stacking faults are of no use to enhance the stress-induced epsilon m artensitic transformation and they rather hinder the transformation. I ntersections of epsilon/epsilon plates and/or epsilon plates/stacking faults were frequently observed. Since the gamma is almost equally str engthened in the 0 degrees and 90 degrees samples by the training, the slight increase in the shape recovery strains in the 90 degrees sampl es compared with the non-treated samples is presumably resulted from t he existence of higher back stress.