Effect of Long Term Thermal Aging on Mechanical Properties of Gas Turbine Blade Coatings
Akihiro ITO, Yuji SUGITA, Shigeo SAKURAI and Jun KAMEDA
Abstract:This paper describes the effect of thermal aging at 870 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 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 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. Key Words:Gas turbine blade, MCrAlY coating, Aluminizing, Nickel-base superalloy, Directionally solidified alloy, Mechanical property, Thermal aging, Small punch test, Ductility, Low cycle fatigue