Minimization of atomic displacements as a guiding principle of the martensitic phase transformation

TL;DR

This paper introduces a geometric minimization approach for understanding martensitic transformations in steel, explaining key features like habit planes and orientation relationships without relying on energy-based models.

Contribution

It presents a novel, assumption-free geometric method that unifies various mechanisms of martensitic transformation and explains experimentally observed features.

Findings

Reproduces the Kurdjumov-Sach orientation relationship

Predicts the habit plane as {225}_γ

Explains the occurrence of Pitsch orientation in thin films

Abstract

We present a unifying description for the martensitic transformation of steel that accounts for important experimentally observable features of the transformation namely, the Neumann bands, the interfacial (habit) plane between the transformed and untransformed phases and their orientation relationship (OR). It is obtained through a simple geometric minimization of the total distance traveled by all the atoms from the austenite (FCC or $\gamma$) phase to the martensite (BCC or $\alpha$) phase, without the need for any explicit energy minimization. Our description unites previously proposed mechanisms but it does not rely on assumptions and experimental knowledge regarding the shear planes and directions, or external adjustable parameters. We show how the Kurdjumov-Sach orientation relationship between the two phases and the $\{225\}_\gamma$ habit plane, which have both been extensively reported in experiments, naturally emerge from the distance minimization. We also propose an explanation for the occurrence of a different orientation relationship (Pitsch) in thin films.