Abstract
In recent studies of very high cycle fatigue, a unique phenomenon of nano-structural refinement has been observed beneath fracture surfaces due to a large number of repeating contacts of themselves over 10^7 cycles. Focusing on this phenomenon, this study proposed a new surface treatment named Cyclic Press Method to refine metal surface without profound plastic deformation. A low cyclic compressive load was given to the surface of Ni-Cr-Mo steel (SNCM439) and Al-Si-Cu die-casting alloy (ACD12) for 5×10^7 cycles. After that, the longitudinal section was processed by FIB and was observed with SIM. As a result, the nanocrystalline structure was clearly formed in the surface layer of both materials. The size of nano-grains and the depth of nano-layer were different between two materials; however, the Cyclic Press Method was shown to be effective in nano-structural refinement of metal surface.
