TaC Modification of High-density C/C Surface and Its High Temperature Oxidation Resistance

The work aims to study the preparation process and microstructure of TaC modified layers on the high-density C/C surface, and to analyze the high-temperature oxidation resistance of the TaC modified layers. In this paper, 2.5 D puncture C/C composites with high density of 1.8 g/cm3 were used as matrix, and its size was φ15 mm×10 mm, the mixed solution of TaCl5 and anhydrous ethanol was selected as the impregnation solvent, and the mass percentage concentration of Tacl5 was 6%. Firstly, the C/C matrix was impregnated by a self-developed vacuum pressurized impregnation system, and the impregnation process parameters were designed as follows: the impregnation time was 5 min, 15 min, 25 min and 35 min respectively; the impregnation times was 5, 7, 9, 11, 13, 15 respectively; the vacuum for impregnation was 8×10–1 Pa and the impregnation pressure was 2 MPa. Secondly, the C/C matrix after impregnation was reduced in hydrogen environment to reduce TaCl5 to Ta, and the process parameters were designed as follows: the reduction temperature was 800 ℃; the reduction time was 5 min. Finally, the C/C matrix after hydrogen reduction was heated at high-temperature to make Ta in-situ reaction with C in C/C matrix to form TaC, and the process parameters were designed as follows: the heating temperature of in-situ reaction was 1 900 ℃; the reduction time was 8 min. According to the TaC modified layer prepared by the above processes, the phase composition of the TaC modified layer was analyzed by an X-ray diffractometer (XRD), the volume density was used to characterize the density of C/C matrix under different impregnation processes such as impregnation time and impregnation times, the cross-sectional morphology and elemental composition of the TaC modified layer were characterized by an environmental scanning electron microscope and an energy dispersive spectrometer (SEM). The oxygen-acetylene flame was used to test the high-temperature oxidation resistance of the TaC modified layer. XRD analysis showed that the modified layer consisted of C and TaC. The results of volume density test showed that the volume density of C/C matrix increased rapidly and then slowed down with the increase of impregnation time and impregnation times. The volume density of the C/C matrix reached 1.88 g/cm3 under the conditions of impregnation time of 15 min and impregnation times of 11. The results of high power SEM observations showed that TaC particles in the TaC modified layer were droplet-shaped or cluster-shaped, 1-3 μm in size, unevenly and discontinuity distributed in the C/C matrix. The results of high-temperature oxygen-acetylene test showed that the surface of the TaC modified layer after the test was formed with a thickness of about 30 μm to 40 μm and a relatively complete structure of the viscous Ta2O5 layer, and the quality loss rate was only 1.9% when the oxidation time was 50 s. It is only 1/6 of the mass loss rate of pure C/C composite material. In conclusion, vacuum pressure impregnation and high temperature in situ reaction method can generate TaC modified layers on the high-density C/C surface, which improves the high temperature oxidation resistance of C/C composites. © 2023 Chongqing Wujiu Periodicals Press. All rights reserved.