Impact of atomic size misfit on lattice distortion in AlFeCoNiX (X = Cr/Mn/Zr) multicomponent alloys

This study investigates the complex interplay among composition, microstructure, and hardness within the high-entropy alloy (HEA), AlFeCoNiX (X-Cr/Mn/Zr). Utilizing the vacuum arc melting process, compositionally graded alloys were fabricated and characterized in their as-cast condition. Microstructural analysis unveiled a complex blend of phases, including BCC, B2, FCC, and C15 (Laves) with the addition of Cr, Mn, and Zr to the quaternary AlFeCoNi HEA. Particularly noteworthy was the dominant Al-Ni-rich phase. The B2 chemical ordering within the Al-Ni-rich phase decreased significantly from 63.5% in AlFeCoNi to 4.5%, 28.8%, and 51% with the addition of Cr, Mn, and Zr, respectively. Furthermore, lattice distortion variations, determined by the atomic size difference parameter δ[%], for AlFeCoNiX (X = Cr, Mn, Zr) HEAs ranged from 5.25 to 10.12. Nanoindentation tests showed hardness variations when Cr, Mn, and Zr were added to AlFeCoNi HEA, ranging from 4.63 ± 0.18 GPa to 4.36 ± 0.19 GPa, 4.39 ± 0.38 GPa, and 9.25 ± 0.57 GPa, respectively. This hardness increase could be correlated with the atomic size difference parameter δ[%] and to the increased inherent defects within the Al-Ni-rich phase of the as-cast HEAs. Overall, this research underscores the potential for customizing high-entropy alloy properties through chemical composition adjustments, catering to specific demands.