(Cr,Al)N/(Cr,Al)ON Oxy-nitride Coatings deposited by Hybrid dcMS/HPPMS for Plastics Processing Applications

Abstract

In plastics industry injection molding and extrusion tools are subjected to adhesive and abrasive wear by the flowing hot melt during extrusion process and adhering solidified melt. Due to their beneficial properties, Cr-based nitride hard coatings deposited by physical vapor deposition (PVD) are applied as protective coatings. In this regard, especially Cr-based oxy-nitride coatings with increased oxygen contents have a high potential to be used on plastic processing tools. In the presented work, five different oxy-nitride monolayer and bilayer coatings (Cr,Al)N/(Cr,Al)ON were synthesized on tool steel substrate AISI 420 (X42Cr13, 1.2083) by means of a hybrid direct current and high power pulsed magnetron sputtering (dcMS/HPPMS) process. Further, the coating architecture was varied in order to compare oxy-nitride monolayers with nitride coatings comprised of thin oxy-nitride top layers. All coatings were investigated with regard to their coating properties and, as defined by the corresponding coating/substrate interactions, with regard to their compound properties. The interactions between the coatings and Makrolon® 2408 polycarbonate (PC2408) were also characterized by means of high temperature contact angle and adhesive tensile strength measurements. Complementary, in-depth chemical analysis of the surface oxide regions of the coatings by means of X-ray photoelectron spectroscopy (XPS) was performed and revealed that the surface oxide composition is primarily determined by the oxygen concentration in the coating bulk. Further, this resulted into high contact angles of the polycarbonate melt, which is desirable for injection molding. All coated samples exhibited a better demolding behavior of the solidified plastic melt as compared to uncoated AISI 420.