Ablation properties and mechanism of a novel La2Hf2O7 coating

Based on excellent thermal stability and high melting point, La₂Hf₂O₇ coating was prepared on SiC coated C/C composites by SAPS. When exposed to a heat flux of 3.2 MW/m² for 20 s, the maximum surface temperature reaches 2240 °C, and the linear and mass ablation rates are 0.0030 mm/s and 0.0001 g/s, respectively. The chemical composition of the ablated La₂Hf₂O₇ coating remained unchanged, and the coarsening of La₂Hf₂O₇ grains caused a denser surface morphology with some pinholes and microcracks, which was attributed to thermal accumulation and scouring of heat flux. Owing to the low thermal conductivity, most of the heat was concentrated on the superficial region, promoting the outer La₂Hf₂O₇ coating to evolve into a dense block structure with some defects, and the inner La₂Hf₂O₇ coating maintained the initial structure. Because of the dense structure and low oxygen permeability of LaHf₂O₇ coating, the inner SiC coating was well protected without oxidation. Moreover, the nano-indentation results show that the hardness of La₂Hf₂O₇ coating increased from 6.39 to 15.67 Gpa, which was ascribed to the intense solid-state sintering of La₂Hf₂O₇ coating.