Abstract
CrWN glass molding coatings were deposited by plasma enhanced magnetron sputtering (PEMS). The microstructure and thermal stability of these coatings were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscope, atomic force microscope and nanoindentation tests. The as-deposited coating exhibited an aggravated lattice expansion resulting in a constant hardness enhancement. The vacuum annealing induced surface coarsening and the spinodal decomposition of the coating accompanied by the formation of nm-sized c-CrN, c-W2N, and h-WN domains. The annealed coating with low W content had mainly a face-centered cubic (f.c.c) matrix, strain fields caused by lattice mismatch caused hardness enhancement. Following an increase in W content, the annealed coating showed a mixed face-centered cubic (f.c.c) and hexagonal close-packed (h.c.p) matrix. The large volume fraction of h-WN phases seriously weakened the coating strengthening effect and caused an obvious drop in hardness.
Highlights
IntroductionOptical glass lenses have a broad range of applications (e.g., telescopes, cameras, medical equipment, and high-power lasers) because of their good refractive index, excellent chemical stability, light permeability, and high image quality [1,2,3]
Optical glass lenses have a broad range of applications because of their good refractive index, excellent chemical stability, light permeability, and high image quality [1,2,3]
Based on the SEM and AFM characterizations, we found that the annealed coatings underwent various degrees of surface coarsening, which was likely triggered by surface oxidation
Summary
Optical glass lenses have a broad range of applications (e.g., telescopes, cameras, medical equipment, and high-power lasers) because of their good refractive index, excellent chemical stability, light permeability, and high image quality [1,2,3]. Precision molding has low cost, high efficiency, can be applied to net forming, and is environmentally friendly. These characteristics have attracted great interest from optical manufacturers [5,6,7]. The adhesive wear of glass blanks greatly degrades the molding life of the forming die and eventually decreases the quality of the optical glass component surface [8,9]. It has been reported that protective coatings can effectively improve the anti-sticking and anti-wear performance of forming dies [10,11,12,13,14,15,16,17,18].
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