ABSTRACT This study systematically investigates the effects of AlCu addition on the microstructural evolution and mechanical properties of (FeCoCrNi) 100‐ x (AlCu) x ( x = 0, 5, 10, 15, 20; at%) high‐entropy alloys (HEAs). The results reveal that the microstructure evolves from coarse equiaxed to refined equiaxed, dendritic, and ultimately dual‐phase morphology with increasing AlCu content. Furthermore, the nanoscale structure evolution was investigated by the small‐angle neutron scattering (SANS) technique. The results show that with 10 at% AlCu addition, spinodal decomposition (with a wavelength of λ SD = 1.3 nm) occurred in the FCC matrix. This structure evolved into L1 2 ‐ordered precipitates (with a radius of 2.15 nm and a volume fraction of 14.68%) within the dendrites, accompanied by interdendritic FeCr‐rich BCC and Cu‐rich B2 phases, upon increasing the AlCu content to 15 at%. It is found that the addition of AlCu induces the internal friction (IF) peaks shift to lower temperatures with enhanced intensity, exhibiting maximum activation energy at 15 at%, coinciding with BCC precipitation. The microstructure alteration leads to a monotonic increase in the microhardness. Although higher AlCu content can improve yield/tensile strength, it reduces ductility. Notably, the (AlCu)15 HEA achieves an exceptional strength–ductility balance, primarily attributable to the L1 2 precipitation strengthening. This study indicates the critical role of AlCu addition in overcoming the strength–ductility trade‐off of HEAs.
Xie et al. (Sun,) studied this question.