Microstructure and properties of age-hardenable Al xCrFe 1.5MnNi 0.5 alloys

Abstract

Two promising high-entropy alloys (HEAs) Al x CrFe 1.5MnNi 0.5 ( 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. Al 0.3CrFe 1.5MnNi 0.5 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. Al 0.5CrFe 1.5MnNi 0.5 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. Both alloys are workable and show a hardness range of Hv 300–500 in the as-cast, as-forged, as-homogenized and as-rolled states. Al 0.5CrFe 1.5MnNi 0.5 alloy has a higher hardness level than Al 0.3CrFe 1.5MnNi 0.5 one because of its full BCC phase. Both alloys thus can be used as structural parts requiring stronger strength. Both alloys display a significant high-temperature age-hardening phenomenon. As-cast Al 0.3CrFe 1.5MnNi 0.5 alloy can attain the highest hardness, Hv 850, at 600 °C for 100 h, and Al 0.5CrFe 1.5MnNi 0.5 can get even higher hardness, Hv 890. The aging hardening is resulted from the formation of ρ phase (Cr 5Fe 6Mn 8-like phase). Prior rolling on the alloys before aging could significantly enhance the age-hardening rate and hardness level due to introduced defects. Al 0.5CrFe 1.5MnNi 0.5 alloy exhibits excellent oxidation resistance up to 800 °C, which is better than Al 0.5CrFe 1.5MnNi 0.5 alloy. Combining this merit with its high softening resistance and wear resistance as compared to commercial alloys Al 0.5CrFe 1.5MnNi 0.5 alloy has the potential for high-temperature structural applications.