Transformation of DO 24 η-Ni 3Ti phase to face-centered cubic austenite during isothermal aging of an Fe–Ni–Ti alloy

Abstract

The transformation of the grain boundary hexagonal close-packed η-Ni 3Ti (DO 24) precipitates to face-centered cubic austenite (γ) was investigated in an Fe–Ni–Ti alloy using transmission electron microscopy. The heterogeneous nucleation of austenite on the (0001) basal plane of the η-Ni 3Ti precipitate was identified. During the growth of the interface austenite, ordered face-centered cubic (fcc) (L1 2) γ′-Ni 3Ti phase was formed in the η-Ni 3Ti by the climbing of the b → = 1 4 [ 0001 ] edge dislocations. The diffusion of iron from austenite to the γ′-Ni 3Ti phase was detected by electron energy loss spectroscopy analysis, resulting in the disordering of the γ′-Ni 3Ti phase. The transformation sequence is schematically suggested and the transformation mechanism was discussed based on the misfit strain in the η/γ interface.