Multiscale structural evolution and permeability in a commercial carbon/carbon composite under arc-jet ablation

Linking the complex mechanisms of ablation with resulting structural and property changes of carbon/carbon (C/C) composites remains challenging. This work utilizes an integrated experimental framework that connects ablation induced structural changes with transport behavior, including permeability, which has not been previously examined in ablative contexts. The multiscale structural evolution and transport behavior of a commercially available C/C were evaluated in a virgin state and after ablation with HyperMATE, a novel quasi-continuous arc-jet plasma torch. The material was characterized using optical and electron microscopy, μ -X-ray computed tomography, capillary flow porometry, Raman spectroscopy, and X-ray diffraction. Ablation preferentially removed matrix carbon at the surface and denudated fibers into needle shapes. The void fraction increased from 5.29% (virgin) to 9.26% (ablated), driven by collapse of large pores into finer ones and the opening of surface defects into connected pathways. These structural changes created new gas transport channels resulting in an approximately one order-of-magnitude increase in through-thickness permeability, and also disrupted solid conduction pathways, contributing to reduced thermal conductivity. At the atomic scale, ablation induced defects in the turbostratic structure, indicated by asymmetric (002) reflection in XRD. The permeability increase is primarily attributed to meso-macro scale structural changes in the material, and the reduced thermal properties result from the coupled effects of changes at the meso-macro and atomic scales. By employing a commercially available material, this work provides broadly applicable insights into the multiscale mechanisms by which ablation modifies structure and degrades macroscopic transport properties. • A custom quasi-continuous arc-jet plasma torch was used for ablation testing. • Arc-jet ablation drastically increased through-thickness gas permeability. • Ablation disrupted the turbostratic lattice structure. • Thermal conductivity decreased with increasing porosity and lattice disorder. • Multiscale framework is proposed linking ablation to resulting transport properties.