Single‐source‐precursor derived bulk Si<sub>3</sub>N<sub>4</sub>/HfB<sub>x</sub>N<sub>1‐x</sub> ceramic nanocomposites with excellent oxidation resistance
Wei Li, Hanzi Du, Chuanmu Tian, Tianshu Jiang, Jan Bernauer, Marc Widenmeyer, L. Wiehl, Leopoldo Molina‐Luna, Jan P. Hofmann, Anke Weidenkaff, Zhaoju Yu, Ralf Riedel
Abstract
Abstract In the present work, bulk Si 3 N 4 /HfB x N 1‐x ceramic nanocomposites were successfully fabricated via a polymer‐derived ceramic approach. The chemical reaction to form the single‐source precursor was confirmed by FT‐IR and XPS, in which both Si−H and N−H groups of perhydropolysilazane react with borane dimethyl sulfide complex and tetrakis(dimethylamido) hafnium(IV). The investigation of the polymer‐to‐ceramic transformation of the synthesized precursors indicates that Hf‐ and B‐modified PHPS exhibits high ceramic yields of up to 100 wt % after pyrolysis at 1000 °C under ammonia. Moreover, XRD and TEM results show that the SiHfBN ceramics with a molar ratio of B : Hf=5 and 10 resist crystallization at temperatures up to 1500 °C and separate after annealing at 1700 °C into nanocomposites comprising of an α‐Si 3 N 4 matrix with embedded ternary HfB x N 1‐x phases, solid solutions of rock salt‐type HfN and HfB. Based on the investigation, warm‐pressing was applied to fabricate bulk SiHfBN specimens, and the oxidation behavior of samples annealed at 1700 °C was recorded at 1500 °C over a range of oxidation times between 1 and 50 h. The weight changes of Si 3 N 4 /HfB x N 1‐x ceramics with B : Hf molar ratios of 2 : 1, 5 : 1 and 10 : 1 are 4.31 %, 4.37 % and 2.57 %, respectively. The formation of HfSiO 4, B 2 O 3 and SiO 2 during oxidation plays a crucial role for the improvement of the oxidation resistance of the Si 3 N 4 /HfB x N 1‐x ceramics.