Study on α-Al2O3 anti-adhesion coating for molds in precision glass molding

Abstract

Precision glass molding is a significant approach for mass production of high precision glass lenses. However, the adhesion problem, which occurs between glass and mold, seriously affects the lenses quality and mold life. Thus, there is an urgent need to develop an anti-adhesion coating for the mold inserts. With the continuous demand for glass lenses, it is essential to develop an anti-adhesive coating that can be adapted to both visible optical glass and infrared glass. In this study, an α-Al2O3 multilayer coating is deposited on tungsten carbide substrate by chemical vapor deposition and the surface roughness of the coating is improved from 100 nm to 10 nm in Ra by ultra-precision grinding with optimized machining parameters. Two currently used coatings of the rare metal Ta multilayer coating and diamond-like carbon coating are compared with the newly developed coating. Typical dense barium crown optical glass D-ZK3 and chalcogenide glass IRG206 are chosen as testing materials for wettability tests and practical precision glass molding experiments. The experimental results show that α-Al2O3 coating exhibits good anti-adhesion property for both glass materials, while Ta coating is not proper for IRG206 chalcogenide glass and diamond-like carbon coating is not suitable for D-ZK3 optical glass. Considering its excellent properties in oxidation resistance and service life, the α-Al2O3 multilayer coating would be a highly potential anti-adhesion coating for precision glass molding.