Segregation engineering for nanoscale martensite to austenite phase transformation at grain boundaries

This project is about the fundamentals of the martensite to austenite reversion transformation.

In an Fe–9 at.% Mn maraging alloy annealed at 450 C reversed allotriomorphic austenite nanolayers appear on former Mn decorated lath martensite boundaries. The austenite films are 5–15 nm thick and form soft layers among the hard martensite crystals. We document the nanoscale segregation and associated martensite to austenite transformation mechanism using transmission electron microscopy and atom probe tomography. The phenomena are discussed in terms of the adsorption isotherm (interface segregation) in conjunction with classical heterogeneous nucleation theory (phase transformation) and a phase field model that predicts the kinetics of phase transformation at segregation decorated grain boundaries.