Fabrication and mechanical properties of h-BN based composites containing dual glass phases

In this work, h-BN based composites containing amorphous silica and ytterbium silicate glass phases were successfully fabricated by in situ hot pressing process. The powder mixtures of h-BN, Yb₂O₃, SiO₂ and sintering additive (Al₂O₃) were hot pressed at 1880?°C for 1?h under 30?MPa in Ar atmosphere. In the composites, β-Yb₂Si₂O₇ phase produced from the reaction between Yb₂O₃ and SiO₂ disappears completely and transforms to Yb-Si-Al-O glass when the amount of Al₂O₃ is ≥1.5?wt.%. The Vickers hardness, flexural strength, and compressive strength reached the maximum values of 2.38?±?0.08?GPa, 337?±?22?MPa and 950?±?34?MPa, respectively, as 1.5?wt.% Al₂O₃ was added. The strengthening effects were attributed to the fine spherical microstructure of Yb-Si-Al-O glass particles, strong AlO₄] coordination state, and residual compressive stress in glass phases.