(Cr,Al)ON Deposited by Hybrid dcMS/HPPMS: A study on Incorporation of Oxygen

Abstract

There has been remarkable progress in the recent years on development of thin hard chromium based coatings using physical vapor deposition (PVD) for numerous technical fields, e.g. plastic processing. An improved interaction can be achieved between the coating/substrate compounds and the molten plastic using (Cr,Al)ON compared to (Cr,Al)N. Therefore, the (Cr,Al)ON can extend the service life of tools and components by increasing their corrosion and wear resistance in plastic processing. This highlights the necessity of a detailed understanding of this coating. Within this paper, coatings of type (Cr,Al)ON were deposited on tool steel substrate AISI 420 (X42Cr13, 1.2083) in an industrial scale coating unit through three different technologies, namely, direct current magnetron sputtering (dcMS), high power pulse magnetron sputtering (HPPMS) and a hybrid technology, including dcMS and HPPMS. The influence of oxygen on properties such as indentation hardness and modulus was studied using oxynitrides having different oxygen contents. Comprehensive investigations were performed by electron probe micro analyses (EPMA), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Based on the results, there exists no significant dependency of aluminum content in the coating on oxygen content in the reactive gas. The coatings deposited by dcMS have the lowest ratios of Al/Cr, while the HPPMS coatings show the highest ratios. This might be attributed to the decreasing deposition rate of chromium by increasing ion energy. The coating deposited by HPPMS has a significantly higher oxygen content revealing more dissociation of oxygen than nitrogen at higher ion energies. The analyses depict the formation of only cubic phases. The anion/cation ratio δ/ξ increases by increasing oxygen content. Potential reasons for the ratios of δ/ξ > 1 might be attributed to the formation of cubic (Cr,Al)2 + θO3 phases, the enrichment of oxygen at the grain boundaries or the cation vacancies in the cubic metal lattice.