FATIGUE BEHAVIOR OF SURFACE NANOCRYSTALLIZED METALS PRODUCED BY SEVERE SHOT PEENING

Severe shot peening method aimed to generate a nanograined layer over specimens’ surface has been applied on nodular cast iron specimens by means of standard air blast equipment but using peening parameters essentially different from typical ones. Various experimental processes including microscopy observation, microhardness, roughness and X-ray diffraction measurements have been carried out to characterize the treated surface of the specimens. The results confirm the generation of a surface nanocrystallized layer by application of severe shot peening. Rotating bending fatigue tests are performed on the specimens to evaluate the effect of nanocrystallized surface layer on their fatigue strength. The results indicate of fatigue strength improvement notwithstanding the specimen’s very high surface roughness.