Synthesis and tribological investigation of PVD hard coatings deposited via hybrid dcMS/HPPMS for application in plastics processing

Abstract

In the plastics processing industry extrusion process is a widely used manufacturing process. One of the most important requirements for an extruder is the highest possible mass flow rate, low wear on the extruder screw, a corrosion resistance against plastics and the a high melt quality throughout the lifetime of an extruder. In order to influence the interactions between the plastics melt and the extruder surface, the extrusion tools can be modified using an innovative coating technology such as physical vapor deposition (PVD). In this regard, direct current magnetron sputtering (dcMS) and high power pulse magnetron sputtering (HPPMS) hybrid technology offers many advantages, such as high ion flux, dense coating morphology, smooth surfaces and uniform coating thickness distribution on complex geometry components. Within the scope of this paper, ternary and quaternary chromium based nitride (Cr,Al)N and oxynitride (Cr,Al)ON PVD hard coatings, were used as protective coatings due to their mechanical, chemical and tribological properties to reduce wear and adhesion forces between extrusion tools and plastics. These hard coatings were deposited by means of hybrid dcMS/HPPMS technology in an industrial scale coating unit under oxygen gas flow variation (F(O2) = 25 sccm and F(O2) = 50 sccm) on plasma nitrided steel 34CrAlNi7-10 (1.8550). The influence of the oxygen content on the coatings morphology and its chemical composition as well as the tribological and the mechanical properties were characterized. An industrial plastic Makrolon® ET3113, PC, was considered for tribological investigations. Adhesion behavior of molten PC (corresponding the processing temperature) on PVD hard coatings was analyzed by high temperature contact angle measurements. Wear tests were performed by using pin-on-disc-tribometer measurements at room temperature T = 23 °C and a higher temperature T = 150 °C against solid PC. A reduction in the adhesion tendency and friction coefficients through the coating in comparison to the uncoated substrate was observed.