Influence of CLVD thermal gradient on the deposition behavior, microstructure and properties of C/C-ZrC composites

Chemical liquid vapor deposition (CLVD) is a rapid preparation method, but it is rarely involved in fabrication of C/C-UHTCs composites and its technology parameters are hardly discussed. In the present study, C/C-ZrC samples were prepared by CLVD process, and the effects of thermal gradient on the deposition behavior, microstructure and properties were investigated. Results exhibited the density, ZrC content and uniformity of the composites increased as the thermal gradient decreased from 30.4 to 9.8 °C/mm, indicating the deposition behavior was improved gradually. When the thermal gradient was 30.4 °C/mm, the deposition behavior of the specimen was poor, which resulted in the high porosity, small numbers of ZrC blocks and uneven distribution. Therefore, the specimen had a low flexural strength with brittle fracture and poor ablation resistance. As the thermal gradient decrease to 9.8 °C/mm, there was an excellent deposition in the composites, and the composites possessed large amounts of ZrC particles and their dispersion were improved remarkably. In this case, the composites displayed a non-brittle fracture with high strength, and the linear and mass ablation rates were reduced, which indicated an improvement of anti-ablation property. Nevertheless, the deposition was deteriorated evidently when the thermal gradient reached to 0 °C/mm. The density, ZrC content and uniformity of the sample became poor, leading to the decline of mechanical property and ablation resistance.