ガスタービン動翼コーティング材の劣化に関する研究 （第２報） ガスタービン動翼コーティング材の長時間熱時効による機械的特性の変化

Abstract

This paper describes the effect of thermal aging at 870°C for 8000h in air on mechanical properties of aluminized CoCrAlY coatings and directionally-solidified Ni-base superalloy substrates of an advanced gas turbine blade. Small punch tests in a range from room temperature to 950°C in air have shown a strong temperature dependence of mechanical properties of various coating regions and substrate. The near-surface coating region of unaged and thermally aged blades showed low ductility. The internal and near-interface coating regions and substrate softened at room and elevated temperatures by the thermal aging. Ductility of the internal and near-interface coating regions and substrate at elevated temperatures was substantially degraded. Low cycle fatigue tests at room temperature using a small punch technique have shown that the fatigue lives of the near-surface and internal coating regions were reduced by the thermal aging. In the case of the small punch test in vacuum, ductility at 870°C of the thermally aged coating regions and substrate showed higher ductility than in air. The mechanical degradation at elevated temperatures of the coating is discussed in light of the metallurgical evolution and environmental embrittlement.