# Excellent Strength–Impact Toughness Combination of Heterostructured Metastable Fe-Rich Medium-Entropy Alloy

## TL;DR

A heterostructured Fe-rich medium-entropy alloy shows excellent strength and impact toughness at both room and cryogenic temperatures.

## Contribution

A novel heterostructured alloy design achieves superior mechanical performance through cold rotary swaging and post-deformation annealing.

## Key findings

- CRS and PDA created a heterogeneous microstructure with twinned γ-matrix and ultrafine grains.
- The alloy showed excellent σm-KCV combination between −90 °C and +20 °C.
- Cryogenic testing revealed inflections in impact curves, increasing crack propagation energy.

## Abstract

The effect of a heterogeneous structure obtained via cold rotary swaging (CRS) and post-deformation annealing (PDA) on the dynamic mechanical properties of a non-equiatomic 49.5Fe-30Mn-10Co-10Cr-0.5C (at.%) medium-entropy alloy at room and cryogenic temperatures was studied. CRS to a reduction of 92% and subsequent PDA at 500–600 °C developed a heterogeneous structure consisting of a twinned γ-matrix and dislocation-free γ-grains in the rod core and an ultrafine-grained microstructure of γ-phase at the rod edge. Therefore, the maximum stress (σm) value increased. Charpy V-notch impact toughness (KCV) decreased after CRS to a reduction of 18% and stabilized after further straining. However, the contribution of the crack initiation energy consumption (KCVi) increased, while the crack propagation energy consumption (KCVP) decreased. PDA resulted in increases in KCVi and KCVP. A ductile-to-brittle transition occurred from −90 °C to −190 °C. Cryogenic Charpy impact testing of the heterostructured material revealed inflections on impact load–deflection curves. The phenomenon contributed to an increase in KCVP, providing a longer crack propagation path. The heterostructured material possessed an excellent σm-KCV combination in the temperature range between −90 °C and +20 °C.