Internal Degradation of 2.5D C/SiC Composites Under Continuous-Wave Laser Irradiation: Experiments and Phase-Selective Modelling.

Surface recession can underestimate laser-induced damage in 2.5D C/SiC composites because thermochemical degradation extends beneath the visible pit. Infrared thermography and micro-CT data from six laser conditions (400-1600 W·cm-2, 3-12 s), together with SEM/EDS observations, were reanalysed using a layered phase-selective model tracking C, SiC and SiO2 evolution. For the four conditions with resolvable damage, the internal degradation front lay 0.84-1.07 mm below the recession surface. At 800 W·cm-2, the 0.02 mm difference between the 6 and 12 s front depths was below the 25 μm voxel size and within specimen uncertainty. The calibrated model matched rear-centre peak temperatures with a mean absolute percentage error of 4.37%, although larger transient discrepancies remained. Temperatures sampled at the measured front coordinates ranged from 2890 to 3080 K. Relative to 800 W·cm-2 for 12 s, the 1600 W·cm-2, 6 s condition caused greater near-surface SiC consumption and solid-mass loss, while the maximum retained SiO2 density decreased from approximately 360 to 180 kg·m-3. These results distinguish geometric recession from internal degradation and support experimental-front mapping and mechanistic interpretation. The mapped states are condition-specific and do not constitute an independently predicted front criterion.