Dependence of mechanical properties on microstructure of high-textured pyrocarbon prepared via isothermal and thermal gradient chemical vapor infiltration

Abstract

In order to explore the dependence of mechanical properties on the microstructure of high-textured (HT) pyrolytic carbon (PyC), the microstructure and properties of HT PyC specimens prepared by isothermal isobaric chemical vapor infiltration (ICVI) and thermal gradient chemical vapor infiltration (TCVI) processes were investigated. The HT PyC of ICVI was uniform and exhibited a more distinct long-range order compared to that of TCVI. Besides, a spatial gradient in texture existed within the HT PyC of TCVI, demonstrating the micro-nonuniformity of the whole matrix. The orientation angle (OA) of HT layers in TCVI increased gradually from the fiber surface to outside, whereas the OA of HT layers in ICVI with better microcrystalline was nearly similar. According to the results of three-point bending and micro-indentation, the flexural strength, interfacial fracture strength, and micro-hardness of TCVI specimens were slightly higher than those of ICVI specimens. Furthermore, the residual thermal stress distribution of TCVI specimens was complex owing to the spatial gradient in temperature of TCVI process, while the residual thermal stress distribution of ICVI specimens was relatively uniform. This work provides meaningful guidance for the process selection and industrial applications of C/C composites.