(Ti,Zr,Hf,Ta)CN/SiCN: A new ultrahigh-temperature ceramic nanocomposite with excellent mechanical properties and ablation resistance

Dense monolithic (Ti,Zr,Hf,Ta)CN/SiCN ceramic nanocomposites are prepared upon pyrolysis of novel (Ti-,Zr-,Hf-,Ta)-containing single-source-precursors (SSPs) and spark plasma sintering (SPS) with high heating rate. Synthesis, polymer-to-ceramic transformation as well as structural evolution of the nanocomposites are thoroughly investigated. Mechanical properties and air-plasma ablation resistance of the nanocomposites are investigated as well. The results show that the nanocomposites are characterized with multicomponent (Ti,Zr,Hf,Ta)CN nanoparticles uniformly distributed within the SiCN matrix (composed of SiC and/or Si₃N₄). The phase composition and molar ratios of metal elements within the (Ti,Zr,Hf,Ta)CN nanoparticles can be precisely controlled via molecular design of the SSPs and controlling reaction sequence. The nanocomposites exhibit excellent mechanical properties with hardness, Young’s modulus and flexural strength achieving 35~37 GPa, 357~417 GPa and 532~603 MPa, respectively, owing to multicomponent solid solution strengthening and interface strengthening. The linear ablation rate of (Ti_0.1Zr_0.3Hf_0.5Ta_0.1)CN/SiCN with approximately 80wt% (Ti_0.1Zr_0.3Hf_0.5Ta_0.1)CN at 2200 °C is 0.033 μm/s which is 2 orders of magnitude lower than those of other multicomponent ultra-high temperature ceramics (UHTCs) under similar conditions. The excellent ablation resistance can be attributed to the nano-scaled grain size of the multicomponent (Ti, Zr, Hf, Ta)CN phase and its excellent homogeneity within the SiCN matrix, which enables the formation of a continuous and dense oxide layer with Hf(Zr,Ti)O₂ skeleton filled with SiO₂/Ta₂O₅.