Microstructure and property evolution of pyrolysed epoxy-derived CFRP/SiC composites for non-structural thermal protection applications

Epoxy-derived carbon fiber–reinforced polymer composites are promising for lightweight high-temperature applications, yet their performance after thermal conversion strongly depends on processing conditions. This study investigates the effects of pyrolysis atmosphere (vacuum and argon) and SiC particle addition on the microstructure–property relationships of epoxy-based CFRP and CFRP/SiC laminates pyrolyzed at 800 °C. Laminates were fabricated by hand lay-up and vacuum-assisted impregnation, followed by staged pyrolysis. The materials were characterized by density measurement, Shore D hardness, three-point bending, scanning electron microscopy (SEM), and Raman spectroscopy. The results show that the pyrolysis atmosphere plays a dominant role in controlling porosity development and matrix continuity. Vacuum treatment promotes aggressive volatile release, leading to lower density, more severe interlaminar porosity, and greater mechanical degradation than argon. Argon processing enables higher char retention and improved microstructural coherence. SiC addition significantly increases hardness in both green-body and post-pyrolysis states due to its intrinsic rigidity; however, flexural strength in both systems drastically decreases (>93%) after pyrolysis, indicating that bending performance is governed by matrix continuity rather than local hardness. SEM confirms extensive fiber exposure and porous carbonaceous residues, while Raman verifies successful polymer-to-carbon conversion. These findings suggest that epoxy-derived CFRP/SiC systems are more suitable for non-load-bearing thermal protection system (TPS) applications, such as insulating or ablative layers, than structural components.