Role of interface morphology on the martensitic transformation in pure Fe

TL;DR

This study uses molecular dynamics to explore how different interface shapes affect phase transformation in iron, revealing that interface morphology significantly influences transformation mechanisms and temperature-dependent mobility.

Contribution

It provides a comparative analysis of flat and ledged interfaces in martensitic transformation, highlighting the atomic mechanisms and mobility differences.

Findings

Ledges nucleate stacking faults that hinder interface motion.

Flat interfaces show different temperature dependence of mobility compared to ledged ones.

Interface morphology critically impacts phase transformation dynamics.

Abstract

Using classical molecular dynamics simulations, we study austenite to ferrite phase transformation in iron, focusing on the role of interface morphology. We compare two different morphologies; a \textit{flat} interface in which the two phases are joined according to Nishiyama-Wasserman orientation relationship vs. a \textit{ledged} one, having steps similar to the vicinal surface. We identify the atomic displacements along a misfit dislocation network at the interface leading to the phase transformation. In case of \textit{ledged} interface, stacking faults are nucleated at the steps, which hinder the interface motion, leading to a lower mobility of the inter-phase boundary, than that of flat interface. Interestingly, we also find the temperature dependence of the interface mobility to show opposite trends in case of \textit{flat} vs. \textit{ledged} boundary. We believe that our study is going to present a unified and comprehensive view of martensitic transformation in iron with different interface morphology, which is lacking at present, as \textit{flat} and \textit{ledged} interfaces are treated separately in the existing literature.