Ni基単結晶超合金の内在欠陥からの高温疲労き裂発生・伝ぱ寿命および破損寿命下限値の評価

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High temperature fatigue life assessment is one of the important issues in Ni-based superalloys for a gas turbine blade. Generally speaking, however, a superalloy with higher strength has larger scatter in fatigue life at a given cyclic loading condition in comparison with conventional steels and alloys. In this study, focusing on the behaviors of fatigue crack initiation and propagation at the internal defects of eutectic γ' phase in a Ni-based single crystal superalloy (MDSC-7M), a cause of the scatter in the fatigue life of the superalloy was discussed by conducting a series of fatigue tests at 1173K. In particular, the propagation of fatigue cracks initiating at the internal defects was characterized quantitatively by means of the beach-mark method. As a result, the fatigue crack propagation rate could be correlated well with the stress intensity factor range, including a small crack of 100-150μm. It was also found that the crack propagation life (i.e., the number of cycles to failure after crack initiation) was more than 40% of the total life (i.e., the number of cycles to failure). The scatter in the fatigue life of the material tested seemed to be mainly caused by the scatter in the crack initiation life. Finally, the lower limit of the scatter could be successfully predicted with the crack growth simulation conducted for the maximum eutectic γ' phase which should be in a fatigue test specimen.
社団法人日本材料学会の論文
2001-05-15

Ni基単結晶超合金の内在欠陥からの高温疲労き裂発生・伝ぱ寿命および破損寿命下限値の評価

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