SB-12-3(066) Effects of Strain Holding on Creep-Fatigue Micro Crack Initiation Life in Ni-based Single Crystal Superalloy(Thermo-Mechanical Fatigue of Superalloys & Coatings)

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概要

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• Some Ni-based single crystal (SC) superalloys with good high-temperature properties are expected as a promising material for high-temperature blades in the next generation land-type gas turbine. However, it is indicated that the creep-fatigue life of a SC superalloy is much lower than that in pure fatigue without strain hold-time and compressive strain holding results in the worst. In this study, creep-fatigue tests as well as creep-fatigue crack propagation tests at 1173K in a SC superalloy were carried out to quantitatively discuss such life reduction. Here, the crack initiation life (N_i) was calculated by subtracting the crack propagation life (N_p) from the failure life (N_f), after N_p was obtained by means of the beach-mark method. As a result, N_i was found to be reduced under both tensile and compressive strain holding conditions. It was also found from the observation of the outside and fracture surfaces of a failed specimen that the main crack was induced from cracks in the brittle oxide scale formed on the outer surface of the specimen. Thus the reduction in N_i could be atributed to this oxidation effect. So, additional creep-fatigue tests were carried out by using a NiCoCrAlY-coated specimen to avoid the surface oxidation. Consequently, N_i in the coated specimen was drastically improved under tensile and compressive strain holding conditions. Furthermore, comparing N_p among the creep-fatigue test conditions, the mean stress shifting with the number of cycles was found to influence mainly on the crack propagation.

• 一般社団法人日本機械学会の論文
• 2001-06-03

著者

• Nitta Akito

  Komae Research Laboratory Central Research Institute Of Electric Power Industry

• Yamamoto Masato

  Materials Science Department, Central Research Institute of Electric Power Industry

• Yamamoto Masato

  Materials Science Department Central Research Institute Of Electric Power Industry

関連論文

• SB-12-3(066) Effects of Strain Holding on Creep-Fatigue Micro Crack Initiation Life in Ni-based Single Crystal Superalloy(Thermo-Mechanical Fatigue of Superalloys & Coatings)

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