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

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.