Fatigue behavior of notched steel specimens with nanocrystallized surface obtained by severe shot peening

Among severe plastic deformation methods that result in surface nanocrystallization, shot peening has proved to be a promising technique. Application of severe air blast shot peening results in surface nanocrystallization, affects a thick layer of material with high compressive residual stresses but at the same time produces rather high surface roughness. In this study notched specimens with a stress concentration factor common in many structural components have been subjected to severe shot peening process. The mentioned treatment uses peening parameters essentially different from conventional ones. Roughness and X-ray diffraction residual stress measurements as well as microscopy observations have been carried out on the treated specimens. Room temperature rotating bending fatigue tests are performed to evaluate the effect of the treatment on specimens’ fatigue strength. Fracture surfaces have been then observed by scanning electron microscopy. The results indicate a very significant fatigue strength improvement for severely shot peened specimens in spite of their very high surface roughness.