Ablation of vacuum plasma sprayed TaC-based composite coatings

TaC-25 vol%MoSi2 and TaC-25 vol%SiC composite coatings were prepared by vacuum plasma spray on SiC coated C/C composites, aiming to improve their ablation resistance. The phase composition and microstructure of the coatings were characterized by scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction, respectively. The ablation behavior of the coatings was evaluated by a plasma flame over 2000 degrees C for 60 s. TaC coating was also fabricated for comparison. The results showed that MoSi2 and SiC uniformly distributed in the composite coatings. The ablation tests demonstrated that the TaC coating was totally oxidized during the ablation process with significant volume expansion. The formed Ta2O5 was porous and blown away by the gas flow. The surface layer of the TaC-MoSi2 coating was oxidized during ablation and the oxide layer was partially detached from the underneath layer due to the evaporation of MoO3. The TaC SiC coating exhibited a low mass loss of 0.32%, 68% lower compared to the TaC coating, and exhibited excellent ablation resistance. It was thought that the comparatively dense Ta2O5-SiO2 layer formed on the coating surface was beneficial for both the oxidation corrosion and mechanical-erosion resistance. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.