Increasing the static, cyclic and rolling load capacity of silicon nitride by shot peening

The aim of the presented investigation was to further improve a novel shot peening technique in order to extend the increase of the static, cyclic and rolling load capacity for the ceramic silicon nitride while retaining the surface integrity. The shot peening process used in our investigation allows to introduce limited plastic deformation near the surface. The multiple indentations result in a surface layer with high compressive residual stresses. The effect of the shot peening process on the surface integrity was ascertained by X-ray diffraction analysis (XRD), static and cyclic ball-on-plate strength tests and a rolling contact tests. The results show that high compressive residual stresses up to 2 GPa can be introduced in silicon nitride, which may boost the static and cyclic load capacity of the near surface layers up to a factor of 4. The rolling contact tests showed that it was possible to increase the Hertzian pressure by a factor of 3 and the load by a factor of 33.