Polymer Infiltration and Pyrolysis of Modified Carbon–Carbon and Ultra-High-Temperature Ceramic Matrix Composites: Advances in Vacuum-and Vibration-Assisted Processing

Polymer infiltration and pyrolysis (PIP) is a versatile route for densifying carbon–carbon composites (C/CCs) and ultra-high-temperature ceramic matrix composites (UHTCMCs), particularly SiC and UHTC-based systems. It operates at comparatively low temperatures, accommodates complex shapes, and is more cost-effective than chemical vapor infiltration (CVI). However, conventional PIP has intrinsic limitations, including low ceramic or char yield, significant shrinkage and gas evolution during pyrolysis, and the need for many infiltration–pyrolysis cycles to reach useful densities. Recent strategies to reduce these drawbacks include graded-concentration and high-pressure PIP, as well as hybrid CVI–PIP and PIP–reactive melt infiltration (RMI) schemes. In parallel, a separate body of work has shown that vacuum-assisted and vibration-assisted infiltration can improve impregnation quality in carbon or ceramic fiber preforms and in carbon-based UHTCMCs. Yet, these advances are rarely synthesized from a PIP-centered, manufacturing-focused perspective or systematically extended to the densification of porous C/C structures, particularly when high-viscosity modified phenolic or particle-laden preceramic precursors are used. This review summarizes the state of the art in PIP densification and processing–structure–property relationships in modified C/CCs or UHTCMCs and related high-temperature composites. It then examines vacuum- and vibration-assisted infiltration concepts, extracts the underlying fluid- and pore-scale mechanisms, and proposes design principles for enhanced PIP equipment and processes tailored to porous and modified C/C systems for space and defense thermal protection.