Pressure-Induced Martensitic Phase Transformation and Microstructure Evolution in nanograined $\text{Fe}\text{-}7\%\text{Mn}$ Alloy

TL;DR

This study investigates how nanograined Fe-7%Mn alloy undergoes pressure-driven phase transformation from BCC to HCP structure, revealing microstructural evolution and the crystallographic pathway using in situ synchrotron X-ray diffraction.

Contribution

It provides detailed in situ analysis of phase transformation and microstructure evolution in nanograined Fe-Mn alloy under high pressure, highlighting the diffusionless martensitic transformation pathway.

Findings

BCC to HCP phase transition at 11.4 GPa

Coexistence of BCC and HCP phases up to 15.9 GPa

Microstrain anomaly at around 10 GPa

Abstract

The Fe-Mn-based alloys are receiving immense attention due to their applications in the third generation of advanced high-strength steels, owing to their high strength and ductility. A detailed in situ high-pressure structural phase transformation and microstructural evolution in nanograined $\text{Fe}\text{-}7\%\text{Mn}$ alloy has been performed using the axial synchrotron X-ray diffraction technique. The ambient BCC phase of $\text{Fe}\text{-}7\%\text{Mn}$ undergoes pressure-driven structural PT to the HCP phase at 11.4 GPa. Both BCC and HCP phases coexist up to 15.9 GPa; thereafter, they transform into a pure HCP phase, which remains stable up to the maximum pressure of 30.3 GPa. The XRD study reveals that the $(110)_{\mathrm{b}}$ dense crystallographic plane of the BCC lattice transforms into a densely packed $(002)_{\mathrm{h}}$ peak of the HCP lattice following the orientational relationship $(110)_{\mathrm{b}} \parallel (0001)_{\mathrm{h}}$ via diffusionless $ \mathrm{Burger's} $ martensitic crystallographic PT pathway. The evolution of crystallite size and microstrain with pressure shows a distinct change during the structural PT. The microstrain exhibits a sharp anomaly at around 10 GPa, suggesting that the microstructural changes precede the structural PT.