The Analysis of Low Cycle Fatigue Behavior in a Nickel Based Superalloy
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Nickel superalloy, low cycle fatigue, tensile hold time, fatigue life, microstructure analysis, fracture analysisบทคัดย่อ
The deformation behaviour and damage mechanisms of the wrought nickel based superalloy EI 698 VD has been investigated under creep/fatigue loading conditions. The alloy was subjected to a load controlled isothermal low cycle fatigue at 650oC with superimposed hold periods of constant tensile load simulating creep stress components. The introduced hold periods were in the range of 1 minute to 10 hours. The pure fatigue and pure creep tests were conducted as well. The tests were of tension–tension type defined by stress ratio R = 0.027. During hold periods a constant stress of σ = 740 MPa was maintained corresponding to creep loading. The tests were conducted until fracture. The influence of hold time was evaluated through the deformation behaviour, fatigue life, and fracture mechanisms participating in the failure process. The time to fracture decreased continuously with increasing hold period. Considering the fatigue life achieved after shortening the hold time to 1 minute, the life time measured was more than 10 times higher than in the case of pure creep. The strain rate dependence achieved within this testing showed inverse dependence with respect to the hold time. The microstructure examination of the fractured specimens, using transmission electron microscopy, made it possible to reveal the participating dislocation mechanisms for combined loading. The fracture analysis of broken up specimens showed that fatigue mechanisms participated in crack nucleation and crack propagation of of testing time when the hold time was 30 minutes and less.
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ลิขสิทธิ์ (c) 2003 The Journal of Metals, Materials and Minerals (JMMM)
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