Morphology transition of deformation-induced lenticular martensite in FeNiC alloys

Abstract

The morphology and habit planes of deformation-induced lenticular martensite were investigated by optical and transmission electron microscopy in Fe30Ni and Fe30Ni0.11C alloys. Transitions in morphology were observed with progressive deformation levels going from lenticular to butterfly and to compact martensite for the Fe30Ni alloy and lenticular to butterfly and to small butterfly martensite for the Fe30Ni0.11C alloy. The habit planes changed from {225} f or {259} f for the thermal lenticular martensite to {111} f for the strain-induced martensite. The morphology and crystallography of the small butterfly martensites was also investigated. A change in the orientation relationships from K- S to N- W relations was also observed. These changes were attributed to the contribution of mobile dislocations which modified the shear mode from twinning to slip, and to a plastic accomodation of transformation strains.