Influence of Residual Stresses in heat-treated High-Speed Steels on the Adhesion of CrAlN Coatings

The influence of different mechanical and chemical pre-treatments for heat-treated AISI M3:2 tool steel (~ DIN S 6-5-3) on the coating adhesion of a CrAlN coating is investigated. Surface topography and residual stresses before and after the PVD coating process are examined. Nitriding and grinding with toric grinding pins results in compressive residual stresses in the subsurface, whereas polishing leads to tensile stresses. After the deposition process a decrease of the residual stresses in the substrate material is observed, whereas the stresses in the nitrided surface are not affected. The resulting residual stresses and roughness profiles are correlated with the adhesion of the PVD coating showing a clear dependency on the substrate pre-treatments. Additionally, interactions between the residual stresses in the subsurface and the resulting stress gradient in the PVD coating could be determined by depth profiles. Based on these findings an optimized grinding process can therefore make the additional process step of nitriding obsolete and can provide an improved coating adhesion for an enhanced wear resistance.