Effect of Y2O3 addition on alumina-hex boron nitride composites

Hot-pressing is the only process to densify alumina-hexagonal boron nitride composites. It must be applied at 1750 °C — 40 M Pa, under nitrogen, but it does not reduce the porosity lower than 8% for composites with alumina contents lower than 70 vol%, and leads to anisotropic composites due to the orientation of the boron nitride platelets perpendicular to the pressing axis. Furthermore, the composites' behaviour during their use in the continuous steel casting is mainly due to the porosity and anisotropy.