Fusion and TBC Penetration Characteristics of Volcanic Ash Collected from Active Volcano

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The damage induced by volcanic ash attack in thermal barrier coating (TBC) has been widely reported. This study focuses on actual volcanic ashes that were collected from an active volcano. The fusion properties and penetration characteristics into the TBC are discussed. Volcanic ash collected at Mt. Aso and Mt. Sakurajima was exposed by an electric furnace. It was revealed that the melting temperature of ash varies because of a difference in the chemical composition between different active volcanoes. The TBC sample with pellet-shaped volcanic ash was exposed at a temperature of 1413 K. From the SEM and EDS analysis results, it was clear that the molten volcanic ash is penetrated into the ceramic layer in TBC and a dense microstructure is formed by the penetration. It was also found that volcanic ash deposition leads to vertical and horizontal cracks in the ceramic layer. The finite element analysis results revealed that vertical cracks were initiated by thermal stress during the heating process. Horizontal cracks were initiated and propagated along the interface by a higher concentration of stress around the interface between the penetration area and the original area in the ceramic coating layer.