Elucidating the role of preferential oxidation during ablation: Insights on the design and optimization of multicomponent ultra-high temperature ceramics

Multicomponent ultra-high temperature ceramics (UHTCs) are promising candidates for thermal protection materials (TPMs) used in aerospace field. However, finding out desirable compositions from an enormous number of possible compositions remains challenging. Here, through elucidating the role of preferential oxidation in ablation behavior of multicomponent UHTCs via the thermodynamic analysis and experimental verification, the correlation between the composition and ablation performance of multicomponent UHTCs was revealed from the aspect of thermodynamics. We found that the metal components in UHTCs can be thermodynamically divided into preferentially oxidized component (denoted as M_P), which builds up a skeleton in oxide layer, and laggingly oxidized component (denoted as M_L), which fills the oxide skeleton. Meanwhile, a thermodynamically driven gradient in the concentration of M_P and M_L forms in the oxide layer. Based on these findings, a strategy for pre-evaluating the ablation performance of multicomponent UHTCs was developed, which provides a preliminary basis for the composition design of multicomponent UHTCs.