FORMATION PROCESS OF LAMELLA STRUCTURES BY DEFORMATION IN AN FE-MN-SI-CR-NI SHAPE-MEMORY ALLOY

For Fe-Mn-Si-Cr-Ni shape memory alloys, it was previously found by HRE M study that the formation of the nanometric lamella structures consis ting of f.c.c.: and h.c.p. phase is very important to exhibit good sha pe memory effect. In the present work, the formation process of such l amella structures has been studied in detail. The results are as follo ws. The transformation is initiated by random formation of extremely t hin martensite plates with 1-2 nm width and then these plates are clus tered and some of them coalesce to form thicker martensite plates with increasing deformation. The clustered regions are 400-600 nm wide and will correspond to the above mentioned lamella structures. These clus tered regions are considered also to correspond to the thinnest marten site plate observable with optical microscope. In the optical microsco pic scale, the thin martenite plates with the smallest width are forme d rather uniformly in an austenite grain, and with further increasing deformation, they are clustered and coalesce into thicker plates with 3-8 mu m width.