Multiscale structural understanding of plasma spraying anti-ablation coating: an example of Ta-Hf-W-C ultrahigh temperature ceramics

The coating formation and structural design of ultra-high temperature ceramics (UHTCs) for aerospace vehicle anti-ablation coatings through plasma spraying remain uncertain despite extensive engineering applications. In this study, (Ta,Hf,W)C/HfC micro-composite, (Ta,Hf,W)C single-phase, and (Ta,Hf,C)/W nanocomposite coatings were successfully prepared using induction plasma spheroidization (IPS), vacuum plasma spraying (VPS), and spark plasma sintering (SPS). Density functional theory (DFT) was employed to capture the electronic structure of (Ta,Hf,W)C _y (y = 1, 0.875, 0.75, 0.5), confirming the influence of carbon vacancies and ceramic metallicity on the plastic forming behavior of sprayed coatings. Additionally, the contribution of HfC to structural stability and WC to the metallicity of carbon-based rock salt-structured UHTCs was elucidated. The pivotal role of carbon vacancies in inducing metastable phase formation and metal phase precipitation for (Ta,Hf,W)C was identified. Ablation behavior variations resulted from differences in multi-scale coating structures, where transverse cracks exhibited more detrimental effects than vertical cracks. Notably, a scale effect of oxidation related to the uniformity of metal elements in the multicomponent ceramic coating was uncovered. It was determined that components capable of forming high melting point oxides should not be uniformly dissolved in the matrix.