Effects of air plasma flame on the ZrB₂-based UHTC coatings: Microstructure, phase evolution and ablation resistance

As for the air plasma sprayed ZrB₂-based coatings, B content change caused by inevitable oxidation is predictable but commonly ignored. Affected by air plasma flame, the B element loss and residual B₂O₃ in the sprayed ZrB₂ coating were observed. Moreover, how the B content change affects the microstructure, phase evolution, and ablation resistance (2.4 MW/m², 60 s) of ZrB₂-based coatings with different secondary phases (SiC, MoSi₂, and TaC) was investigated. The B element loss contributed to the increase in surface temperature and the decline in the sintering degree of the ZrO₂ layer. The evaporation of residual B₂O₃ caused damage to the coating structure in the form of pores, whose negative effect was enhanced and reduced by MoSi₂ and TaC secondary phases, respectively. This work will provide some insight into thermally sprayed non-oxide ceramic coatings in the atmosphere.