Comparison between shot peening and surface nanocrystallization and hardening processes

The surface nanocrystallization and hardening (SNH) is a relatively new process that has been developed to enhance fatigue and wear resistances. The SNH is similar to widely used shot peening (SP) in the sense that both processes entail repeated impacts of the work-piece surface with spheres. The difference between them lies in the sizes of spheres and the impact velocities used. Such a difference results in dramatic changes in kinetic energies and thus the thicknesses of the work-hardened layer and the nano-grained surface layer. In this study, finite element modeling is performed to provide quantitative description of these differences. The results show that the kinetic energy in the SNH process is typically 180 times larger than that in shot peening, and the deformation layer in the SNH process is about 10 times thicker than that generated in shot peening. Furthermore, the maximum plastic strain and the maximum residual compressive stresses in the SNH-processed work-piece are 100 and 10 times larger than those in the shot-peened work-piece, respectively. The implication of these differences on fatigue resistance has been discussed.