A novel atomic movement mechanism of intersection-induced bct-α → bcc-α′ martensitic phase transformation

Abstract

The atomic movements for completing the fcc-γ → hcp-ε → bct-α Plastic Deformation-Induced Martensitic Transformation (PDIMT) has been revealed to be confined purely on one specific {111}γ plane. However, so far nothing has been known for the possible intersection of two fcc-γ → hcp-ε → bct-α PDIMTs pre-developed from two individual {111}γ slip systems. For the first time, here we capture the nucleation of bcc-α′ in the intersection of two bct-α phases in 304 stainless steel, following a novel polymorphic fcc-γ → hcp-ε → bct-α → bcc-α′ PDIMT. High-resolution transmission electron microscopy observations were mainly performed to unveil the underlying atomic process in the final-step bct-α → bcc-α′ transition, which is executed by the cooperation of partial dislocation dipoles gliding on every second {110}α planes of two bct-α phases (equivalent to {110}α′ and {011}α′ planes), and atom shuffling along the [11¯0]α1/[1¯12]α′ and [11¯0]α2/[211¯]α′ directions.