New insights on the ablation mechanism of silicon carbide in dissociated air plasmas

Thermal protection system (TPS) applied in space vehicle is mainly composed of silicon carbide (SiC) and related components. When exposed in re-entry flows, the SiC based TPS may suffer from severe ablation if the surface temperature is beyond a critical threshold (generally ≥1600°C). Unveiling the ablation mechanism of SiC is thus vitally important to define the borders of service and to help optimize the TPS structures in re-entry environments. Motivated by this, this work uses an inductively coupled plasma wind tunnel to generate the dissociated air plasmas and explores the ablation behaviors of several SiC materials (including SiC ceramic and SiC fiber reinforced SiC matrix composites). Some new insights are acquired based on the detailed analysis of the surface characteristics prior to and after ablations. First, the role of surface roughness on the critical ablation temperature of the SiC based composite is put forward. Second, a ‘from-point-to-surface’ ablation process due to the surface roughness during the short ‘temperature jump’ is proposed, which is an important supplementary to the existing ablation model of SiC; Finally, a smoother surface with less defects is concluded to efficiently enhance the ablation resistance of the SiC based TPS in re-entry environments.