Microstructure and room/elevated-temperature mechanical properties of hot-pressed h-BN composite ceramics with La2O3-Al2O3-SiO2 addition

Hexagonal boron nitride (h-BN) composite ceramics were fabricated by hot pressing using h-BN, La2O3, Al2O3 and amorphous SiO2 as the raw materials. The effects of La2O3-Al2O3-SiO2 addition on the bulk density, apparent porosity, microstructural evolution and room/elevated-temperature mechanical properties of h-BN composite ceramics were investigated. The results indicated that liquid phase generated by the reaction of La2O3-Al2O3 and SiO2 exhibited a good wettability with h-BN grains, contributing to fill the pores and improve the densification. Therefore, h-BN composite ceramics with synchronous introduction of La2O3-Al2O3 and SiO2 show the better mechanical properties compared with separate addition of La2O3-Al2O3 or SiO2. h-BN composite ceramic incorporated with 10 vol.% La2O3-Al2O3 and 20 vol.% SiO2 shows the highest room-temperature strength of 266.4 MPa and elevated-temperature strength of 389.0 MPa at 800 degrees C.