Chemical fluctuation enabling strength-plasticity synergy in metastable single-phase high entropy alloy film with gigapascal yield strength

In this work, we synthesized a FeCoNiCrCu high entropy alloy film (HEAF) via magnetron sputtering, which exhibited a metastable single FCC phase with random chemical distribution. Owing to the metastable nature, the as-deposited atomic structure affords nano-scale chemical fluctuation induced by moderate thermal annealing without causing phase transition. Compared to the single-phase FCC metals hitherto reported, our as-deposited and thermally annealed HEAFs exhibited the highest yield strength (3.4-4.2 GPa) under microcompression due to the combined action of nano-grains and growth twins. Furthermore, according to our experiments and atomistic simulations, plasticity-strength synergy was achieved as the nano-scale chemical fluctuation was able to promote deformation twinning in the HEAFs. The outcome of our research provides not only an atomistic understanding of the strength-plasticity synergy in the metastable FCC HEAFs with gigapascal yield strength, but also a facile method to design high performance metastable chemically complex metallic films.