Influences of fracture toughness and thermal conductivity on the ablation behavior of SiC-ZrC-MPCFs composite modified by mesophase-pitch-based carbon fibers

A novel SiC-ZrC-MPCFs composite was successfully prepared by introducing short-cut mesophase-pitch-based carbon fibers (MPCFs) into SiC-ZrC ceramics. Results show that the MPCFs improved the fracture toughness of SiC-ZrC-MPCFs composite to 4.97 +/- 0.47 MPa m1/2, which was 58.06 % higher than that of SiC-ZrC ceramics. Due to the reinforcement of MPCFs, no cracks were formed on the composite during ablation, thus preventing the direct diffusion of oxidizing atmospheres into the interior. Moreover, the MPCFs also worked as thermally conductive channels and provided a thermal conductivity of 68.10 +/- 0.68 W/(m K) for the composite, compared to 39.48 +/- 1.25 W/(m K) for SiC-ZrC ceramics. The heat could rapidly transfer from ablation center to other areas through the MPCFS, leading to low ablation center temperatures. The COMSOL simulation indicates that the ablation center temperature of SiC-ZrC-MPCFs composite was 1094 degrees C after 2300 degrees C plasma ablation for 20 s, while that of SiC-ZrC ceramics was up to 1543 degrees C, which was confirmed by the actual back temperatures. Therefore, the improved fracture toughness and high thermal conductivity ensured the excellent ablation property of SiC-ZrC-MPCFs composite. After ablation for 20 s, the ablation rates of the composite were -0.048 +/- 0.007 mg/s and -0.715 +/- 0.056 mu m/s, respectively.