A strategy for synergistically enhancing mechanical and antibacterial properties of copper-bearing high-entropy alloys: Surface nanocrystallization

Ultrasonic Surface Rolling Process (USRP) enhances the mechanical properties of metals through severe plastic deformation and surface nanocrystallization. However, the microstructure evolution and strengthening mechanisms of Cu-bearing high-entropy alloys (HEAs) under USRP remain unclear due to their complex phase structures. In this study, we improve the mechanical and antibacterial properties of CrFeNi 0.5 Cu 0.3 HEA through USRP-induced surface nanocrystallization. We find that the USRP maintains the matrix phase (austenite, ferrite, and Cu-rich phase) but leads to grain refinement in austenite and Cu-rich phase through continuous and nanotwinning-assisted dynamic recrystallization. Taking the 10-pass USRP as an example, the yield strength increases by 47% from 341 MPa to 490 MPa due to dislocation strengthening, grain refinement, nano-twins, and hetero-deformation-induced stress in austenite. The fracture behavior transitions from ductile fracture to cleavage fracture as the failure is dominated by ferrite-related cracks. Finally, we find that USRP conserves the excellent antibacterial properties of the Cu-bearing HEA (>93%), confirming that the 10-pass USRP is the optimal strengthening parameter. The above results demonstrate that USRP is an effective means of promoting the application of Cu-bearing HEAs in the medical field.