Shot peening of hard chromium coatings. Damage or benefit?

Brittel materials tend to the behavior of failure before deformation at room temperature. Thus, strengthening of brittle materials due to deformation induced compressive residual stresses has been thought to be not advantageous. Nevertheless, investigations on ceramics, which are real brittle materials, had shown that, using specific parameters, shot peening can introduce high compressive residual stresses into the near-surface and improve the near-surface strength. Based on these results preliminary investigations have been performed to apply the ceramics-specific shot peening technique to the brittle hard chromium coatings which up to now have not been subjected to this beneficial mechanical surface treatment process. The very first results reported here show that it is possible to convert the typical tensile residual stresses in chromium coatings into very high compressive residual stresses. These compressive stresses act as crack closing forces, increase the strength under static and cyclic loading conditions and are expected to additionally improve the resistance against wear of the coatings and corrosion of the substrate.