A study on the formation mechanisms of butterfly-type martensite in Fe-30% Ni alloy using EBSD-based orientation microscopy

The spatial orientation distribution and crystal orientation relationships (ORs) between a butterfly-type martensite (α′) plate and its austenite matrix (γ) in Fe-30% Ni alloy were investigated in detail. One α′-γ interface of the α′ plate mainly exhibits a G-T (Greninger-Troiano) OR, while the other side shows both Kudjumov-Sachs and G-T ORs. It is proposed that the difference between the two sides arises due to a change of the accommodation process for transformation strain during the growth of α′. Moreover, orientations inside the α′ plate continuously change from the one α′-γ interface to the other. A similar orientation change is observed in the γ matrix but only on one side of the plate. These orientation gradients have a common rotation axis and are explained in terms of dislocation inheritance during the growth of the α′ plate. Based on the local changes of ORs at α′-γ interface and the orientation gradients inside α′ and γ, the α′ formation process is discussed.