Abstract
CrWN coatings with tungsten content ranged from 4.1 at.% to 23.4 at.% were fabricated by adjusting the input power on a tungsten target through the ion beam assisted deposition (IBAD). After tungsten doping, lattice parameter of the CrWN was expanded from 4.16 to 4.22 Ǻ, and only the face centered cubic phase of the CrN was observed. Due to the solid solution strengthening, an apparent increase on the hardness was exhibited, and maximum hardness, 23.9 GPa was reached. In addition, the critical load and residual stress were measured. It was found that coatings revealed excellent critical load higher than 80 N as compressive stress below 2.5 GPa. Surface roughness and crystallite size of the CrWN coatings were analyzed by an atomic force microscopy and the Scherrer formula, respectively. With 4 at.% W doping, more than 50% decrease on the crystallite size was revealed, and a lower surface roughness around 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. It was demonstrated that CrWN coatings with 4.4 to 16.7 at.% tungsten doping, exhibiting enhanced hardness and smooth surface morphology, could be considered as the potential candidate coating for practical use in glass molding. CrWN coatings were annealed at 750 oC in air atmosphere for the oxidation test. According to the XRD and the depth profile, it was identified that the formation of Cr2O3 would induce the surface roughness larger than 40 nm for both CrN and CrWN coatings. CrWN1 was then selected as protective coating for molding test. After molding test for 100 hours, surface roughness of glass preform maintained 6~8 nm and was satisfactory for precision criterion.