Microstructural evolution and mechanical properties of Cu-based alloy by post-sintering ultrasonic nanocrystal surface modification

In this study, an ultrasonic nanocrystal surface modification (UNSM) was used to enhance mechanical properties of CuSn10Pb10 alloy. Top surface coarse grains were refined into nano-grains (mean size of 45–74 nm) after UNSM. Mechanical testing results revealed that the surface hardness, yield strength and ultimate tensile strength increased after UNSM owing to the formation of nano-grains containing some nano-twins that can be elucidated according to the Hall-Petch relationship. Grain size refinement mechanism was attributed to the increase in dislocation density and the formation of new dislocations, where the accumulation of them at low-angle grain boundaries caused a variation of the grain orientation.