Shock-compression microstructure transformation of the additive manufactured FeCoNiAlTi high-entropy alloy

Investigation into the microstructural deformation mechanisms of a high-entropy alloy (Fe_28.0Co_29.5Ni_27.5Al_8.5Ti_6.5 (at%)) prepared by laser additive manufacturing and aging treatment, with a three-phase nanocomposite structure, is carried out via shock compression experiments using plate impact. Microstructural characteristics and compositions are inspected using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The microstructure of the high-entropy alloy is comprised of high-density dislocation structures, high-volume-fraction L1₂ nano-precipitates, a small amount of L2₁ nano-precipitates, and face-centered cubic (FCC) matrix phases. The lattice arrangement of the FCC matrix phase is disordered, with strong segregation of Fe and Co atoms, while Ni, Al, and Ti atoms are predominantly present in the ordered L1₂ and L2₁ nano-precipitates. The FCC matrix or the FCC matrix with high-density stacking faults are bounded by a 9R-phase between two phase boundaries. The mechanisms of microstructural transformation of the high-entropy alloy are discussed in detail.