FORMATION OF HCP AND FCC TWINS IN AN FE-MN-CR-SI-NI ALLOY

Microstructure at the intersection between h.c.p. plates has been examined in a shape memory alloy Fe-Mn-Cr-Si-Ni after deformation below the T0 temperature. By analysing the microstructure, it is found that the second shear system transmits through the other at the expense of formation of h.c.p. twins. The twinning plane is identified to be either {1011BAR} or {1012BAR}, satisfying the orientation relationship with respect to the fc.c. matrix given by [1010BAR]//[011BAR], (0001)//(100) for (1011BAR) twin and [1010BAR]//[111BAR], (0001)//(211BAR) for (1012BAR) twin. An f.c.c. twin has also been found at the growing front of the two h.c.p. plates. On the basis of these observations twinning mechanisms of h.c.p. and f.c.c. phases in the Fe based SME alloy are discussed.