火山灰堆積したニッケル基超合金の組織崩壊に関する研究

抄録

Recently, a volcanic eruption has been attracted attention. If Mt. Fuji is exploded, many gas turbines (GTs) located along Tokyo bay would be exposed to a threat of volcanic ash. The volcanic ash could be deposited on the turbine blade, and it is expected to cause a degradation of nickel-based superalloy as the substrate of turbine blade. In this study, a high-temperature exposure test was conducted for volcanic ash deposited IN738LC sample, and its degradation of microstructure was discussed by SEM observation and EDX analysis. As a result, it was found that oxide formation was controlled under shorter exposure time condition, because volcanic ash deposition interrupted supply of oxygen. On the other hand, the oxide layer brought about enough time for Al diffusing toward the surface under longer exposure time condition, which led to disappearing of γ′ phase beneath the surface. The dissipation of γ′ phase also affected Vickers hardness distribution in comparison with the bared sample. Thus, it was revealed that volcanic ash deposition reduces mechanical strength of IN738LC due to collapse of microstructure.