Strengthening mechanism and wear behavior of AlCrFeNiNb_x high-entropy alloys from the perspective of phase modulation

AlCoCrFeNi high-entropy alloys have consistently attracted research attention due to their outstanding strength-to-ductility ratio. However, the substantial content of expensive cobalt in these alloys has somewhat limited their engineering applications. Consequently, there is an urgent need to design and develop high-performance, low-cost cobalt-free high-entropy alloys. AlCrFeNi alloys exhibit microstructures and properties similar to AlCoCrFeNi alloys. Simultaneously, the absence of Co significantly reduces costs and markedly improves casting performance. These alloys represent a potential structural material for harsh environments, demonstrating promising engineering applications. In order to explore the phase modulation mechanism of Nb element on AlCrFeNi alloy, this study combines experiments with first principles calculations to systematically investigate the effects of Nb on microstructure, mechanical properties and wear resistance of AlCrFeNi alloy. The results show that the AlCrFeNiNb_0.4 high-entropy alloy has the best mechanical properties and wear resistance.The doping of Nb changes the wear mechanism of the AlCrFeNi alloy and improves the wear resistance of the alloy. This is attributed to the phase modulation effect of Nb on AlCrFeNi alloy: on the one hand, it induces the precipitation of Laves phase with high hardness, and on the other hand, it solidly dissolves in the BCC and B2 phases of the alloy, and significantlyimproves the mechanical properties of the two phases. In addition, Nb doping refines the microstructure of the AlCrFeNi alloy, which leads to an increase in the phase interface density, thus enhancing the hardness, yield strength and wear resistance of the alloy. First principles calculations show that the Nb atoms change the electronic structure of the BCC and B2 phases in the AlCrFeNi alloy, which enhances the stability of the two phases, confirming the solid solution strengthening of the two phases by Nb. The Nb atoms form strong antibonds with most of the atoms in the two phases, which further explains the nature of the generation of a large number of Laves phases in the microstructure of the alloy after Nb doping.