Mechanical Properties and Strengthening Mechanisms of FCC-Based and Refractory High-Entropy Alloys: A Review

Abstract

The excellent mechanical properties of high-entropy alloys, especially under harsh service environments, have attracted increasing attention in the last decade. FCC-based and refractory high-entropy alloys (HEAs) are the most extensively used series. However, the strength of FCC-base HEAs is insufficient, although they possess a great ductility and fracture toughness at both room and low temperatures. With regard to the BCC-based refractory HEAs, the unsatisfactory ductility at room temperature shadows their ultrahigh strength at room and high temperatures, as well as their excellent thermal stability. In order to strike a balance between strength and toughness, strengthening mechanisms should be first clarified. Therefore, typical mechanical performance and corresponding strengthening factors are systemically summarized, including the solid solution strengthening, second phase, interface, and synergistic effects for FCC-base HEAs, along with the optimization of principal elements, construction of multi-phase, the doping of non-metallic interstitial elements, and the introduction of kink bands for refractory HEAs. Among which the design of meta-stable structures, such as chemical short-range order, and kink bands has been shown to be a promising strategy to further improve the mechanical properties of HEAs.