Circumventing strength-ductility paradox in high entropy alloys through deformation processing

Abstract

Engineering materials are known to show trade-off between high tensile strength and ductility. The simultaneous enhancement of strength and ductility can make them more appealing for various structural applications. In this study, we demonstrate a facile technique to address the conflicting strength-ductility trade-off in crystalline materials. AlCoCrFeNi high entropy alloy (HEA), one of the most popular multi-principal alloy system, was considered for the investigation. The as-cast AlCoCrFeNi alloy showed a coarse grain microstructure with BCC/B2 phase. The as-cast alloy was subjected to severe plastic deformation using a facile technique known as stationary friction processing (SFP). The SFP for only 15 min resulted in an order of magnitude reduction in the grain size along with BCC to FCC phase transformation. The processed sample demonstrated more than 2 times higher ultimate tensile strength (∼650 MPa) compared to as-cast HEA (∼310 MPa). Further, the ductility of the processed HEA was enhanced from 11 % to 18 %. The combination of fine grain structure along with BCC to FCC transition through SFP enabled exceptional mechanical properties in the HEA. This approach can easily be extended to other alloy systems for designing high tensile strength and superior ductility.