NEW STRUCTURES AFTER MARTENSITIC-TRANSFORMATION IN AN FE-MN-SI-CR SHAPE-MEMORY ALLOY

The stress-induced martensitic transformation and the microstructures of Fe-28Mn-6Si-5Cr (%) alloy subject to several training cycles at dif ferent temperatures were investigated with transmission electron micro scopy (TEM) and X-ray diffraction (XRD) in detail. Some new structures of 4H-(2, 2) and 6H-(3, 3) with orthogonal lattice were found, and th e corresponding transformation shear models were also proposed. The oc currence of the orthogonal structures was the result of shear accomoda tion to the impeded stress-induced gamma-->epsilon transformation and the reverse transformation, and was supposed to be unfavourable to the improvement of shape memory effect (SME).