Processing of chromium tungsten nitride hard coatings for glass molding

CrWN coatings were obtained on WC substrates by ion beam assisted deposition (IBAD). The surface roughness and crystallite size of the CrWN coatings were analyzed by atomic force microscopy and X-ray diffraction, respectively. With 4 at.% W doping, more than 50% decrease in crystallite size was found, and smaller surface roughness of about 2 nm was obtained due to the reduced crystallinity. This provided satisfactory surface condition requirements of 10 nm with practical optical accuracy for glass molding die. In addition, coatings were heated at 750 °C in air atmosphere for oxidation test. Formation of Cr2O3 would induce the surface roughness larger than 40 nm for both CrN and CrWN coatings. According to AES profile, coating CrWN1, with 4.4 at.% W, revealed similar penetration depth of oxygen in comparison to CrN, which was noted for excellent oxidation resistance. Therefore, comparable anti-oxidation behavior was expected for the CrWN coatings with low tungsten contents. It was demonstrated that CrWN coatings with 4.4 to 16.7 at.% tungsten alloying, exhibiting smooth surface roughness and improved hardness, could be considered to possess optimum composition for practical use.