Surface chemistry of PVD (Cr,Al)N coatings deposited by means of direct current and high power pulsed magnetron sputtering

摘要

(Cr,Al)N protective coatings were deposited using direct current (DC) and high power pulse magnetron sputtering (HPPMS) technology. The chemical analysis of the surface near region of the coatings was performed by means of X-ray photoelectron spectroscopy (XPS) and was correlated to the deposition parameters and resulting coating morphology. A surface oxidation process was observed by means of angle resolved XPS studies and XPS sputter profiles. Both DC and HPPMS coatings showed a non-stoichiometric chemical composition with a significant excess of cations (chromium and aluminum) in the bulk structure, leading to a metastable phase. The passivation reaction of the surface near region leads to an anion to metal ratio which goes along with an enrichment of aluminum in the surface near region as a thermodynamically favored composition in equilibrium with the ambient atmosphere. Interestingly, the variation of the pulse duration of the HPPMS process, which led to a change of the peak current, had a strong influence on the resulting composition of the surface near region.