Hybrid dcMS/HPPMS PVD nitride and oxynitride hard coatings for adhesion and abrasion reduction in plastics processing

During plastics extrusion, machine components such as extruder screw and extrusion die are exposed to the plastics melt. The resulting tribological loads can lead to excessive wear. In this regard, chromium based nitride and oxy-nitride hard coatings deposited via physical vapor deposition offer great potential in order to protect machine components against wear. In order to produce PVD coatings with increased mechanical properties on complex geometries such as extruder screws the high power pulsed magnetron sputtering/high power impulse magnetron sputtering technology seems to be promising. In this paper Cr-Al-N and Cr-Al-O-N coatings deposited on plasma nitrided steel 34CrAlNi7 10 (1.8550) by a direct current magnetron sputtering hybrid PVD process are investigated. The Cr/Al ratio and the O content of the coatings were varied. Chemical composition, morphology and structure were analyzed by means of scanning electron microscopy, X-ray photo spectroscopy and X-ray diffraction, respectively. High temperature contact angle measurements at the processing temperatures of the plastics were conducted in order to analyze the adhesion behavior of the (coated) surfaces towards industrial relevant types of polyamide, polycarbonate and polypropylene. The tribological behavior of the (coated) surfaces against plastic pins at ambient temperature was investigated in a pin-on-disc tribometer. The contact zones between the (coated) surfaces and the plastics were analyzed by Raman spectroscopy. Furthermore, the wear behavior was investigated. The results reveal a correlation between the chemical composition of the coatings and the adhesion towards the investigated plastics.