The microstructures and properties changes induced by Al:Co ratios of the AlXCrCo2-XFeNi high entropy alloys

The formation High Entropy Alloys (HEAs) from combinations of multiple principal elements, with differing molar ratios, has led to the suggestion that the properties of HEAs must be dramatically changed. In this study, a series of five-component Al_XCrCo_2-XFeNi HEAs were prepared by using spark plasma sintering (SPS). The effect of the Al:Co ratios on the phases and microstructures of Al_XCrCo_2-XFeNi HEAs were investigated. It was found that the microstructures changed from a Fe- and Cr-rich face-centered cubic (FCC) structure to a Ni- and Al-rich body-centered cubic (BCC) structure with an increase in the molar ratios of Al:Co; clearly different morphologies of the four HEAs were observed. The crystal structures of the Al_XCrCo_2-XFeNi HEA evolved from FCC + σ + disordered BCC + ordered BCC structures to σ + disordered BCC + ordered BCC structures, and then to disordered BCC + ordered BCC structures. Moreover, the wear behavior and compression behavior of the samples at x = 1.0, 1.2, 1.4, and 1.6 were investigated. With an increase molar ratios of Al:Co, the series of Al_XCrCo_2-XFeNi HEAs exhibited different wear and fracture mechanisms. The results showed that the Al_1.6CrCo_0.4FeNi alloy exhibited good wear resistance, and the Al_1.4CrCo_0.6FeNi alloy exhibited good combinations of strength and ductility. The close relationship between the microstructures and mechanical properties of the HEAs are discussed with a focus on balancing the strength and plasticity of the alloys for practical applications.