Interface structure and grain growth behavior of Ta₄HfC₅-Si₂BC₃N complex ceramic

The ultrahigh-temperature ceramic (UHTC) Ta₄HfC₅ is one of the most promising candidate materials suitable for the use in hypersonic aircrafts because of its excellent thermophysical and thermomechanical performance. However, the poor sintering ability is one of the main reasons restricting its potential application. To overcome this obstacle, Si₂BC₃N ceramic was used to densify the tantalum hafnium carbide solid solution. Thus, dense Ta₄HfC₅-Si₂BC₃N ceramics were synthesized by hot-pressing sintering. The resulting composite ceramic was comprised of crystalline Ta₄HfC₅, SiC and BN(C) phases. A “tadpole-like” shape of SiC and BN(C) connecting phase was formed accompanied by rapid grain growth at 2100°C, increasing the fracture toughness to 3.47 ± 0.12 MPa m^1/2. The growth mechanism of the Ta₄HfC₅ grains gradually changed from grain-boundary sliding by volume diffusion to grain boundary diffusion, attributed to the grain growth activation energy changing from 112.4 to 250.7 ± 29.3 kJ mol⁻¹ with increasing sintering temperature.[Figure not available: see fulltext.]