Superior Resistances to High-Temperature Treatment and Ablation of A6B2O17 (A = Zr, Hf; B = Nb, Ta) Multicomponent Ceramics

Multicomponent oxide ceramics yield great promises in next-generation thermal protection systems according to their high potential for thermal stability and ablation resistance, but their protective mechanisms remain unclear. In this study, the five multicomponent A 6 B 2 O 17 (A = Zr, Hf; B = Nb, Ta) oxide ceramics with different atomic concentrations, respectively, at A- and B-sites, were prepared via a solid-state reaction with a rapid cooling process. Their phase, structural evolutions, and the properties under high-temperature treatment and dynamic ablations were investigated to reveal thermal stability and anti-ablation mechanisms. Only the (Hf 1/2 Zr 1/2 ) 6 (Ta 1/2 Nb 1/2 ) 2 O 17 with equal molar ratio both at A- and B-sites maintained the A 6 B 2 O 17 phase after heat treatment at 1773 K for 25 h; the other samples underwent phase separation behaviors. In addition, the (Hf 3/4 Zr 1/4 ) 6 (Ta 2/3 Nb 1/3 ) 2 O 17 ceramic showed excellent ablation resistance (∼2500 K, 100 s) with the thinnest oxide layer. This property is attributed to the formation of “skeleton-filler phase” protective composite layer, as the (Zr, Hf)O 2 “skeleton” owns high melting point and low volatility to resist thermal gas erosion, and the A n B 2 O 2n+5 family fills defects and hinders the penetrations of O 2 . This study expects to offer design for advanced thermal barriers suitable for the next-generation hypersonic vehicles and reusable spacecraft.