Effect of annealing environment on the microstructure and mechanical property of CrWN glass molding coating

The CrWN glass molding coating was synthesized by plasma enhanced magnetron sputtering (PEMS). The effect of annealing environment (e.g., vacuum, N-2 and Air) on the microstructure and mechanical property of as-deposited coating was investigated by the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), atomic force microscope (AFM) and nanoindentation tests. Results showed that the as-deposited coating exhibited dense columnar structure consisting of multilayer CrN and W2N phases. The vacuum annealed coating showed similar thickness to that of as-deposited coating, but underwent visible surface coarsening because of slight oxygen erosion. The N-2 and air annealed coatings suffered from varying degree of oxidation damage accompanied by the formation of mixed WO3-CrWO4 phases, which consequently resulted in severe thickness expansion and surface coarsening. The vacuum annealing induced a spinodal decomposition of supersaturated solid solution to form nm-sized CrN and W2N domains. Strain fields originating from the lattice mismatch eventually caused a pronounced age-hardening in the vacuum annealed coating. Whereas the N-2 and air annealed coatings showed significant mechanical degradation because these loose WO3-CrWO4 oxides degraded the stable matrix structure. Our results clearly demonstrated that vacuum environment effectively suppressed the oxidation damage and mechanical degradation of glass molding coating.