Single‐source‐precursor derived bulk Si₃N₄/HfB_xN_1‐x ceramic nanocomposites with excellent oxidation resistance

Abstract

In the present work, bulk Si3N4/HfBxN1‐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‐Si3N4 matrix with embedded ternary HfBxN1‐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 Si3N4/HfBxN1‐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 HfSiO4, B2O3 and SiO2 during oxidation plays a crucial role for the improvement of the oxidation resistance of the Si3N4/HfBxN1‐x ceramics.

Hard and tough novel high-pressure γ-Si 3N 4/Hf 3N 4 ceramic nanocomposites

“…18 wt% and is much less than those for nanotwinned diamond at 1100 ℃ (75 wt%) [64], diamond/c-BN composite at 1100 ℃ (80 wt%) [65], nano diamond at 1000 ℃ (45 wt%) [16], and natural diamond at 850 ℃ (87.5 wt%) [64] and is finally stabilized at that temperature. The Siand Hf-oxide layers formed by the oxidation of the γ-Si 3 N 4 /Hf 3 N 4 nanocomposite prevent further oxidation compared with the oxidation of diamond to continuously form CO/CO 2 [64,66].…”