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

Abstract

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.