High-pressure synthesis, mechanical properties, and oxidation behavior of advanced boron-containing α/β-Si <sub>3</sub>N <sub>4</sub>/Si ceramics using polymer-derived amorphous SiBN ceramics
Wei Li, Shuailing Ma, Siwen Cui, Jingxue Ding, Marc Widenmeyer, Xiaoqi Zhang, Ying Zhan, Zhaoju Yu, Wenshu Zhang, Pinwen Zhu, Tian Cui, Anke Weidenkaff, Ralf Riedel
Abstract
The preparation of dense Si<sub>3</sub>N<sub>4</sub>-based ceramics has attracted great attention because of the achievable improvements in their mechanical properties and high-temperature oxidation resistance. In this work, advanced dense boron-containing α/β-Si<sub>3</sub>N<sub>4</sub>/Si monoliths were prepared via a high pressure‒high temperature technique in which polymer-derived amorphous SiBN powders were used as raw materials. The crystallization behavior and phase transformation of the polymer-derived amorphous samples were studied in the temperature range from 1400 to 1800 °C. The results demonstrate that the incorporation of boron in the Si<sub>3</sub>N<sub>4</sub> matrix suppresses the phase transformation from α-Si<sub>3</sub>N<sub>4</sub> to β-Si<sub>3</sub>N<sub>4</sub>. Furthermore, the mechanical properties of the as-prepared samples were measured, and the maximum hardness and fracture toughness of boron-rich SiBN samples reached 14.8 GPa and 7.96 MPa·m<sup>1/2</sup>, respectively. The hardness of the obtained boron-rich SiBN samples is stable up to 300 °C. In addition, the oxidation behavior of the samples prepared at 1400 and 1600 °C was investigated at 1400 °C for 50 h. The results show that the incorporation of boron significantly improved the oxidation resistance of the samples because of the formation of borosilicate/cristobalite. This work provides guidance for the synthesis of boron-containing α/β-Si<sub>3</sub>N<sub>4</sub>-based ceramics with excellent mechanical properties and oxidation resistance.