Interphase boundary structure and accommodation mechanism of lenticular martensite in Fe–Ni alloys

Abstract

This study investigates the interphase boundary structures of lenticular martensites in Fe–33Ni and Fe–31Ni, and discusses the accommodation mechanism for transformation strain. Despite the large difference in the macroscopic morphology of the interphase boundary, the nature of interfacial dislocations in both alloys is almost the same; there are two sets of screw dislocations with a/2 [ 1 ¯ 1 ¯ 1] M and a/2 [1 1 ¯ 1] M Burgers vectors on the interphase boundary. On the basis of the array of interfacial dislocations, the shear planes of dislocations with a/2 [ 1 ¯ 1 ¯ 1] M and a/2 [1 1 ¯ 1] M Burgers vectors were determined to be (1 1 2) M (=(1 0 1) A) and ( 1 ¯ 1 2) M (=(0 1 1) A). Two sets of interfacial dislocations accommodate the atomistic misfit strain due to the change in the stacking sequence and the shape of parallel close packed planes. The macroscopic transformation strain and elastic strain energy of lenticular martensite are also reduced by the presence of the observed lattice invariant deformations.