Surface hardening after hard coating deposition - combining TiAlN tribological coatings with subsequent electron beam treatment

In this investigation an electron beam hardening (EBH) procedure was applied to heat-treatable steel 51CrV4 coated with Ti(1-x)AlxN hard coatings, where x ranged from 0.3 to 0.6. The coatings with variable composition and mechanical properties were deposited by reactive magnetron sputter deposition. For electron beam surface hardening followed by hard coating deposition, the energy distribution within the energy transfer field caused a nearly constant hardening temperature on the treated material surface. Morphology, composition and mechanical properties of the coatings remained nearly unchanged, whereas the coating-substrate interface and the steel surface region were highly modified. Diffusion of interface-near coating elements into the substrate occurred and the corresponding region of the substrate showed clear changes in morphology and composition. These changes can be correlated with substantial improvements of the coating adhesion properties. Based on temperature measurements and calculations of electron penetration depths a plausible description of the observed effects was derived. The electron beam hardening caused a significant improvement of delamination resistance, especially for coatings with insufficient adhesion properties.