Microstructure and properties of age-hardenable AlxCrFe1.5MnNi0.5 alloys

Two promising high-entropy alloys (HEAs) AlxCrFe1.5MnNi0.5 (x = 0.3 and 0.5) were designed from Al–Co–Cr–Cu–Fe–Ni alloys by substituting Mn for expensive Co and excluding Cu to avoid Cu segregation. Microstructures and properties were investigated and compared at different states: as-cast, as-homogenized, as-rolled and as-aged states. Al0.3CrFe1.5MnNi0.5 alloy in the as-cast, as-homogenized and as-rolled states has a dual-phase structure of BCC phase and FCC phase, in which Al, Ni-rich precipitates of B2-type BCC structure disperse in the BCC phase. Al0.5CrFe1.5MnNi0.5 alloy in the corresponding states has a matrix of BCC phase in which Cr-rich particles of BCC structure and Al, Ni-rich precipitates of B2-type BCC structure disperse. These three BCC phases have the same lattice constant. lloys are workable and show a hardness range of Hv 300–500 in the as-cast, as-forged, as-homogenized and as-rolled states. Al0.5CrFe1.5MnNi0.5 alloy has a higher hardness level than Al0.3CrFe1.5MnNi0.5 one because of its full BCC phase. Both alloys thus can be used as structural parts requiring stronger strength. lloys display a significant high-temperature age-hardening phenomenon. As-cast Al0.3CrFe1.5MnNi0.5 alloy can attain the highest hardness, Hv 850, at 600 °C for 100 h, and Al0.5CrFe1.5MnNi0.5 can get even higher hardness, Hv 890. The aging hardening is resulted from the formation of ρ phase (Cr5Fe6Mn8-like phase). Prior rolling on the alloys before aging could significantly enhance the age-hardening rate and hardness level due to introduced defects. Al0.5CrFe1.5MnNi0.5 alloy exhibits excellent oxidation resistance up to 800 °C, which is better than Al0.5CrFe1.5MnNi0.5 alloy. Combining this merit with its high softening resistance and wear resistance as compared to commercial alloys Al0.5CrFe1.5MnNi0.5 alloy has the potential for high-temperature structural applications.