SB-12-4(117) The effect of Service Exposure on Mechanical Properties of Gas Turbine Blade Coatings(Thermo-Mechanical Fatigue of Superalloys & Coatings)

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This paper describes the effects of in-service exposure under combustion of liquefied natural gas on the microstructure, chemical composition and mechanical properties in aluminized CoCrAlY coatings deposited over directionally solidified Ni-base superalloy substrates of advanced gas turbine blades. The results of the service-exposed coating were compared with those of the unexposed one. The unexposed and service-exposed coatings consisted of four layers with different microstructure and chemical composition. In-service environmental attack led to the deposition of Fe oxides on the top aluminized coating. While in-service, Ni diffused extensively from the substrate into the near-surface coating region. The interdiffusion of Ni/Co resulted in the formation of Al/Ni rich intermetallic phases in all the coating regions, except a near-surface coating region indicating Cr rich phases. In the internal coating region, Cr rich phases disappeared. During in-service exposure, the near-interface coating region softened at RT and elevated temperatures. The fracture strain of the internal and near-interface coating regions at elevated temperatures was substantially degraded. In-service mechanical degradation of the aluminized CoCrAlY coatings is discussed in light of the microstructural change and the susceptibility to oxygen-induced embrittlement.
一般社団法人日本機械学会の論文
2001-06-03