Solubility, crystal growth, and film-formation mechanism of NbC-modified ZrC coating under oxyacetylene flame

Herein, the ablation resistance of plasma-sprayed NbC-modified ZrC (ZrC-NbC) coatings was firstly tested using an oxyacetylene flame. Next, the phase composition of the ZrO2-Nb2O5 (NbO2.5) plates heat-treated at 2100 degrees C in an argon atmosphere was determined. The results indicated that, the ZrC-20 mol% NbC coating formed a dense oxide layer after ablation for 120 s and a composite film consisting of self-bridged ZrO2 columnar crystals up to 300 s, achieving the best ablation property. At 2100 degrees C, the solubility (solid solubility and adsorption capacity) of niobium suboxide in ZrO2 was 30 mol%. The stable phases were t-ZrO2 and Nb as the NbO2.5-addition was no more than 20 mol%, and t-ZrO2, Nb, and NbO when it ranged from 25 to 40 mol%. Furthermore, ZrO2 increased the viscosity of Nb-O liquids and ensured the transformation of NbO2.5 into Nb and NbO phases, improving the thermal stability. Nb-O liquids improved the transfer of Zr and formed gradients of temperature and oxygen concentration, strengthening the film-forming ability of the ZrC coating under an oxyacetylene flame.

Automated summary

The ablation resistance of plasma-sprayed NbC-modified ZrC coatings was tested with an oxyacetylene flame. The phase composition of the heat-treated ZrO2-Nb2O5 plates was determined. The results showed that the ZrC-20 mol% NbC coating had the best ablation property, forming a dense oxide layer and a composite film of ZrO2 crystals.