Self-healing performance of niobium suboxide-based solid solution for UHTC coating during oxyacetylene test

In this work, NbC coatings modified with different contents (0, 25 and 50 mol%) of HfC were deposited on SiC-coated C/C composites via supersonic atmospheric plasma spraying to study the effect of HfC on the ablation-resistance of the NbC coatings under an oxyacetylene torch. The phase composition and chemical states of Nb₂O₅–66.67 mol% HfO₂ plates heated up to 2100 °C in an Ar atmosphere were investigated. The results confirmed that the effective ablation time of the NbC-coating mixed with 50 mol% HfC was approximately 120 s, which is more than twice that of the pure NbC coating. During air quenching, NbO and NbO₂ ultimately transformed into Nb₂O₅, producing compressive stress that stabilized the t-HfO₂ crystals. Furthermore, the formation of hafnium oxide significantly improved the thermal stability and viscosity of the Nb–O film, and the niobium suboxide-based solid solution, possessing an attractive self-healing performance, increased the compactness of the HfO₂-based solid solution layer are responsible for the superior ablation performance of the NbC-HfC coating.