Insights into the microstructural evolution and ablation mechanism of HfC_xN_1−x ceramics subjected to extreme laser ablation

Hafnium carbonitride (HfC_xN_1−x) ceramics show great potential for thermal protection systems due to their ultra-high melting point, and investigating their ablation behavior is essential for their application under extreme conditions. In this work, HfC_xN_1−x ceramics with varying nitrogen contents were synthesized via polymer-derived ceramic followed by spark plasma sintering. Laser ablation tests showed that HfC_0.75N_0.25 achieved excellent ablation resistance under the laser power of 500 W, with linear and mass ablation rates of 1.08 µm s⁻¹ and 0.32 mg s⁻¹, respectively. This is ascribed to the high melting point and exceptional thermal stability of HfC_0.75N_0.25, which result from moderate nitrogen incorporation. During laser ablation, dislocation accumulation and the formation of lath-like structures dissipate part of the laser heat flux. Subsequently, a dense Hf(C, N, O) solid solution layer with high viscosity forms, which effectively impedes oxygen diffusion and maintains stable ablation resistance of HfC_0.75N_0.25. Conversely, excessive nitrogen incorporation induces the formation of the Hf₇O₈N₄ phase with numerous defects and crack nucleation, ultimately deteriorating laser ablation resistance. These findings provide useful insights for the design and development of ultra-high temperature ceramics for applications in extreme environments.