Effect of abnormal grain refinement on synchronous strengthening behavior of Fe₅₀Mn₃₀Co₁₀Cr₁₀ high entropy alloys

Improving processing efficiency while obtaining excellent material formation and mechanical properties is the primary concern of the manufacturing industry. This study aims to refine the grains of Fe₅₀Mn₃₀Co₁₀Cr₁₀ high entropy alloy during friction stir processing, achieving exceptional tensile properties in the stir zone by increasing the rotational speed. The key driver behind grain refinement lies in the alloy's inherently low stacking fault energy, with the primary recrystallization mechanism being discontinuous dynamic recrystallization. The freshly recrystallized fine grains share analogous microstructures and energy levels during severe plastic deformation, which engenders a state of increased competition among them. This robust competitive dynamic impedes grain growth, thereby promoting the development of refined grains. This microstructure proves instrumental in avoiding premature microcracking during tensile loading by hindering martensite formation, consequently improving the UTS and EL of the material. Nevertheless, the high heat input and substantial strain result in an increase of temperature and strain energy in the system, eventually disrupting the high energy system and causing grain coarsening as the rotational speed continues to increase. This coarsened grain and high martensite fraction lead to premature initiation of cracks under tensile loading, which is not conducive to further improvement of tensile properties.