Ablation resistance and mechanism of niobium carbide coatings fabricated by plasma spraying

Nb-SiC and Nb-SiC-Al system niobium carbide composite coatings were developed in-situ by plasma spraying NbSiC and Nb-SiC-Al system composite powders, respectively. As a comparison, NbC-Al2O3 system niobium carbide composite coating was developed ex-situ by plasma spraying NbC-Al2O3 composite powder. The ablation resistance of the three systems of niobium carbide composite coating was evaluated under plasma jet. The results showed that the Nb-SiC and Nb-SiC-Al system coatings developed in-situ have better ablation resistance than NbC-Al2O3 system coating. The microstructure of Nb-SiC and Nb-SiC-Al system coatings after different times of ablation was characterized by scanning electron microscopy to investigate the ablation mechanism. The results showed that the surface of the coating of both systems can form Nb2O5 film under ablation conditions to isolate the further penetration of oxygen and heat into the coating. The Al2O3 in the Nb-SiC-Al system coating reacted with Nb2O5 to form AlNbO4. The formation of AlNbO4 promoted the densification of Nb2O5 film, so that the Nb2O5 film formed on the surface of the Nb-SiC-Al system coating was uniform and dense, which improved the ability of the coating to resist plasma jet ablation.