Abstract: Volcanic ashes are posing increasingly severer threats to the aviation safety. As the operation temperature of the turbine engine elevates, molten volcanic ash leads to the degradation of the thermal barrier coatings (TBCs) and eventually catastrophic engine failure. However, the physical and chemical properties of volcanic ashes vary due to the distinct chemical compositions, rendering it extremely challenging to evaluate the effects of each ash material on the failure of TBC. Here, we proposed a new metric termed Basicity to investigate the influence of chemical composition on the melting temperature and viscosity of volcanic ashes. Artificial CaO-MgO-Al₂O₃-SiO₂ materials (CMAS) were synthesized to simulate the wetting, spreading and corrosion behavior of volcanic ashes at 1300 °C on (Gd_0.9Yb_0.1)₂Zr₂O₇ (GYbZ), a model TBC material. Our results reveal that the synthetic CMAS does not fully capture the damage caused by volcanic ash due to the difference in compositions. The viscosity and characteristic temperatures decrease as the Basicity value increases, indicating its significant impact on the fusion properties of ashes. Notably, distinct from CMAS, the unexpected presence of Fe₂O₃ in volcanic ashes promotes the formation of garnet phase, conversely impedes the formation of apatite dense layer. These findings provide valuable insights into the corrosion mechanisms caused by TBC and strategies for TBC protection against volcanic ashes.

Key words: Volcanic ash, Basicity, Thermal barrier coatings (TBC), Wetting behavior, Corrosion mechanism