A Comprehensive Study on High-Temperature Oxidation Behavior of Ceramic Molds for Hot Embossing

Structural ceramics are potential mold materials for hot embossing, due to their superior mechanical strength as well as low thermal expansion coefficient. However, the service time of molds, especially those in high-temperature hot embossing, strongly depends on their oxidation resistance. As a result, the oxidation behaviors of various ceramics (e.g., SiC, ZrO₂, AlN, Al₂O₃, Si₃N₄ and WC) were investigated by conducting cyclic oxidation experiments in this study. Mass changes of ceramic samples thermal treated under different temperatures were measured by thermogravimeter (TGA) and precision electronic balance. The structural and chemical compositions of ceramic samples were detected by X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDXS). The surface morphology of the samples was characterized by scanning electron microscopy (SEM), and the surface roughness of the samples was measured by white light interferometry. The mechanical properties of the samples were evaluated by a microhardness tester and nanoindentation instrument. It is noted that Al₂O₃ shows negligible oxidation within 1000 °C. ZrO₂ maintains a decent surface roughness of below 32 nm and a stable hardness within 1000 °C. SiC has the highest hardness at high temperatures, and its surface roughness increases notably above 800 °C. The surface roughness of Si₃N₄ and AlN soars between 600 °C and 800 °C. The surface finish of WC is significantly deteriorated above 600 °C. Therefore, the appropriate embossing temperature of Al₂O₃ ceramics is below 1000 °C, that of ZrO₂ ceramics is between 800 °C and 1000 °C, that of SiC ceramics is below 800 °C, that of Si₃N₄ and AlN ceramics is between 600 °C and 800 °C, and that of WC ceramics below 600 °C.