Argon plasma–induced compressive residual stress for simultaneous strength–ductility enhancement in a CoCrFeMnNi high-entropy alloy

Surface modification techniques, such as shot peening and ultrasonic nanocrystal surface modification, are widely used to improve wear, corrosion, and fatigue resistance, as well as strength by tailoring the near-surface microstructure. However, the severe plastic deformation accompanying these processes often results in high dislocation densities and limited strain accommodation capability, leading to a deterioration of ductility. In this study, argon plasma bombardment introduces a graded compressive residual stress field at the surface while reducing dislocation density in a CoCrFeMnNi high-entropy alloy. This surface modification simultaneously increases yield strength, tensile strength, uniform elongation, and total elongation, demonstrating a simple route to enhance strength–ductility synergy without severe surface deformation.