Ultra-strong nano-structured high-entropy AlCoCrFeNi alloy films reinforced by Al2O3 addition

In this study, Al2O3-reinforced high-entropy alloy (HEA) films of AlCoCrFeNi with nano-crystalline and amorphous structures were fabricated via magnetron sputtering. After they were subjected to oxide dispersion strengthening, the fabricated films exhibited nano-crystalline BCC/FCC solid solutions and 3.6 nm nano-scale Al2O3 spheres embedded in amorphous shells, the amorphous shells and defect-free nano-crystals hindered the dislocation movements. The film exhibited a high-hardness value of 10.6 GPa and elastic modulus of 183.9 GPa, which subsequently increased by 43% and 35%, respectively. The Hall-Petch formula and Orowan model were used to predict the strengthening mechanism in the films, and the values of hardness agreed with their corresponding experimental values. The results of introducing Al2O3 via physical vapour deposition to achieve grain refinement and dual-phase nano-structures without heating those obtained by nucleating in the bulk. The study presented a novel concept for producing oxide dispersion strengthened HEAs.