Ultrahigh hardness in nanostructured dual-phase high-entropy alloy AlCrFeCoNiNb developed by high-pressure torsion

Abstract

High-entropy alloys (HEAs) usually show higher hardness compared to conventional alloys due to the presence of five or more principal metals in the solid-solution form, but there are significant efforts for further enhancing the hardness of these alloys. In this study, three strategies are combined to achieve one of the highest hardness levels reported for metallic alloys: (i) solution hardening by the concept of multi-principal element alloys, (ii) grain refinement by severe plastic deformation via the high-pressure torsion method, and (iii) introduction of dual phases to hinder dynamic recrystallization and enhance interface hardening. An ultrahigh hardness of 1030 Hv is achieved by the introduction of nanograins in a dual-phase (cubic + hexagonal) HEA, AlCrFeCoNiNb. Such a high hardness is not only due to the formation of nanograins with an average size of 10 nm, but also due to the generation of dislocations, interfaces and spinodal-like elemental decomposition.