High‐Pressure Synthesis of Amorphous Si3N4 and SiBN‐Based Monoliths without Sintering Additives

Abstract

Amorphous Si3N4 and SiBN monoliths without sintering additives are successfully prepared by high‐pressure–low‐temperature (HPLT) sintering using the single‐source‐precursor‐derived amorphous Si3N4 and SiBN powders as raw materials. The microstructural evolution and crystallization behavior of the as‐prepared samples are investigated using scanning electron and transmission electron microscopy and X‐ray powder diffraction, respectively. The results show that the incorporation of boron in the Si–N network enhances the crystallization temperature up to 1200 °C. The Vickers’ hardness of the HPLT‐sintered Si3N4 sample amounts ≈11.6 GPa whether prepared at 1000 or 1200 °C, while the maximum hardness of the SiBN sample is up to 16.3 GPa. The fracture toughness of amorphous Si3N4 and SiBN5 samples is almost identical (around 2.5 MPa m1/2) whether prepared at 1000 or 1200 °C, and SiBN2 and SiBN5 samples show an improved fracture toughness. In addition, the oxidation resistance of the as‐prepared samples is investigated at temperatures up to 1000 °C. A comparison between amorphous Si3N4 and SiBN monoliths demonstrates a positive effect of the presence of boron on their oxidation resistance.