Mn content optimum on microstructures and mechanical behavior of Fe-based medium entropy alloys

Fe-XMn-5Si-10Cr-0.9C (X = 10, 15, 20, and 25 wt%) medium entropy alloys (MEAs) with different Mn con-tents were prepared by magnetic suspension melting in a water-cooled copper crucible, and casted in a negative pressure suction copper mould. The modified Warren-Averbach equation and the thermody-namic model were used to calculate the alloy dislocation density and stacking faults, respectively. The effects of the Mn content on the phase structure, stacking fault energy (SFE), dislocation density, and mechanical properties of the alloy were investigated. The results indicate that the MEAs possess a low stacking fault energy (-8.50-14.44 mJ/m2) and a unique high as-cast dislocation density (up to 4.8 x 1015 m-2). The microstructure of the as-cast alloys consisted of austenite phase. As loading, the c ? e martensite transformation occurs and is accompanied by obvious work-hardening behaviour. A low SFE and high DSmix improved the storage capacity of the dislocation density, promoted the formation of e-martensite, and improve the strength and plasticity. Both the SFE and DSmix increased with an increase in the Mn content, and the dislocation density initially increased and then decreased. Optimising the Mn content and coordinating the balance between the SFE and DSmix can regulate the optimal dislocation density.(c) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

The study investigated the effects of different Mn contents on the phase structure, stacking fault energy, dislocation density, and mechanical properties of Fe-XMn-5Si-10Cr-0.9C medium entropy alloys. The results showed that a low stacking fault energy and high DSmix contributed to improved strength and plasticity of the alloy.