Microstructures and Mechanical Properties of FeNiCrMnAl High-Entropy Alloys

A series of novel Co-free [FeNi]_75−xCr₁₅Mn₁₀Al_x (x = 0, 5, 10, 15, 20, 25) high-entropy alloys (HEAs) was fabricated by nonconsumable vacuum melting. The solidification structure evolution and mechanical properties were investigated. The results show that with the gradual addition of Al atoms, the metallographic structure varies from a single FCC-phase cellular structure (Al-0, Al-5) to an FCC + B2 dual-phase dendritic structure (Al-10), then to an FCC + BCC + B2 multiphase lamellar structure (Al-15), and finally to a BCC + B2 dual-phase dendritic structure (Al-20, Al-25). The distinctive presence of white approximately spherical CrFe-rich BCC precipitates distributed on the NiAl-rich B2 matrix was observed in Al-20 and Al-25 alloys. In terms of mechanical properties, with an increasing Al content, the strength of the alloy increases, and the plasticity decreases. In particular, Al-20 and Al-25 alloys exhibited desirable mechanical properties and a good combination of high compressive compressibility strengths of 1590 MPa and 1660 MPa with excellent plasticity of 45 and 42%. Furthermore, the strengthening mechanism was classified as solution strengthening, fine crystal strengthening, and precipitation strengthening.