A new guide for improving mechanical properties of non-equiatomic FeCoCrMnNi medium- and high-entropy alloys with ultrasonic nanocrystal surface modification

Ultrasonic nanocrystal surface modification (UNSM) treatment on non-equiatomic medium- and high-entropy alloy (HEA) of Fe-x(CoCrMnNi)(100-x) is firstly introduced and its impact on microstructure and mechanical properties are revealed. By UNSM, severe plastic deformation-induced dislocation and deformation twins (DTs) arise at the topmost surface. Especially, Fe-60(CoCrMnNi)(40) (Fe60), which is classified as a medium-entropy alloy (MEA), exhibits epsilon-martensitic transformation. In the room temperature tensile test, a high strength of similar to 600 MPa and ductility of similar to 65 % elongation (strain to failure) is accomplished in Fe60. Initially formed DTs and epsilon-martensitic transformation by UNSM treatment plays a key role in retardation of necking point via both twinning-induced plasticity and transformation-induced plasticity. However, Fe-20(CoCrMnNi)(80) (Fe20) comparatively shows low strength of similar to 550 MPa and similar to 40 % elongation, owing to the low accommodation of DTs than Fe60. Our research will provide new guidelines for enhancing the mechanical properties of MEA and HEA. (C) 2020 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.