Comparison of ablation performances and sublayer interaction of CVD-(TaC/SiC)₃ alternate coatings with different crystallite morphologies

To compare the influence of crystallite morphology on the synergistic effect between different sublayers under oxyacetylene flame (O₂/CH₄ flux ratio: ~1.33), (TaC/SiC)₃ alternate coatings were prepared on C/C composites by chemical vapor deposition via triple cycles of TaC/SiC sequences, whose TaC sublayers were composed of acicular (AS-6) and columnar crystals (CS-6) respectively. After the cyclic ablation tests with a heat flux of 2.48 MW/m², the CS-6 sample exhibited favorable thermal shock resistance through layer-by-layer protection than coating exfoliation of the AS-6 specimen. Their SiC layers also performed different ablative behaviors, which transformed from acute evaporation of SiO₂ glass for the SiC single layer to the eroded surface with pits distributed of the AS-6 specimen, and further the integrated scale with glass covered of the CS-6 sample. The stress relaxation resulting from the formation of porous middle layer and the enhanced reinforcement of Ta₂O₅ particles for SiO₂ glass to improve evaporation suppression may be the main reasons for the superior synergistic effect of the CS-6 sample.