Single-source-precursor synthesis and air-plasma ablation behavior of (Ti,Zr,Hf)C/SiC ceramic nanocomposites at 2200 °C

Dense monolithic (Ti,Zr,Hf)C/SiC ceramic nanocomposites with four different molar ratios of metallic elements in the (Ti,Zr,Hf)C phase (i.e., Ti:Zr:Hf=1:1:1, 2:3:5, 2:3:3, and 1:2:1) were prepared upon pyrolysis of novel (Ti,Zr,Hf)-containing single-source-precursors (SSPs), followed by spark plasma sintering. A thorough characterization was conducted to elucidate the synthesis of the SSPs, polymer-to-ceramic transformation, chemical/phase compositions and microstructure of the SiTiZrHfC-based ceramics. The results revealed the feasibility of synthesizing the nanocomposites with high (Ti,Zr,Hf)C content using SSP method. These nanocomposites were characterized by a unique microstructure with in situ generated (Ti,Zr,Hf)C@C core-shell nanoparticles homogeneously mixed with β-SiC. The ablation behavior of the nanocomposites was evaluated on an air-plasma device for 60 s. Impressively, the nanocomposites exhibited excellent ablation resistance, and the lowest linear ablation rate reached -0.58 μm/s at 2200 °C. Notably, the ablation resistance can be dramatically improved by precisely tailoring the atomic ratios of metal elements within the (Ti,Zr,Hf)C phase via molecular design of the SSPs. The formation of a multiple-oxides layer with both high-melting-point phase ((Ti,Zr,Hf)O₂) and low-melting-point phases ((Zr,Hf)TiO₄) and glassy SiO₂ as well as their structure played a critical role in the enhanced ablation resistance. The uniform distribution of the high-melting-point (Ti,Zr,Hf)O₂ nano-/micro- particles throughout the glassy SiO₂ matrix significantly enhanced the viscosity and stability of the oxide layer by pinning effect, offering superior protection against the ingress of oxygen atoms and excellent resistance to mechanical erosion.