Tungsten carbide molds for precision glass molding process: Mechanism of high-temperature degradation

Tungsten carbide (WC) is a well-established material used in glass molding field due to its low thermal expansion and high compressive strength at elevated temperatures. During glass molding process, the WC mold has to withstand thousands of thermo-mechanical coupled interactions in the aerobic environment. Understanding the degradation mechanism of WC substrate during precision glass molding is very important for the design and preparation of protective coatings and the optimization of glass molding process. In this study, surface failure analysis of WC substrate was carried out using barrel compression test and ball-to-disk friction test. The microstructures, element compositions, surface morphology of the WC substrates were measured by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and white light interferometer (WLI). Damaging phenomena such oxidation, interdiffusion, spallation, glass sticking, and surface roughening on the WC substrate were observed. The experimental results showed that the WC substrate degraded very rapidly at above 600 °Cand air environment. The fundamental degradable reason of WC substrate is the oxidation, which directly leads to the decrease of the material strength, the aggravation of the wear, occurring of the glass sticking, and the increase of surface roughness. Furthermore, the WC mold microhole array without protective coatings can be used to fabricate the glass microlens array in a suitable glass molding environment. This work provides engineering guidance for the fabrication of glass optics during glass molding process.