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dc.contributor.advisorNeu, Richard W.
dc.contributor.authorKirka, Michael
dc.date.accessioned2015-06-08T18:15:17Z
dc.date.available2015-06-09T05:30:07Z
dc.date.created2014-05
dc.date.issued2014-04-08
dc.date.submittedMay 2014
dc.identifier.urihttp://hdl.handle.net/1853/53458
dc.description.abstractUnderstanding the effects of aged microstructures on the thermomechanical fatigue (TMF) properties of nickel-base (Ni-base) superalloys remains unclear. Few experimental results are currently available in this area, and of the limited results available, some promote aged microstructures as beneficial, while others as detri- mental. The importance of these aged structures arises from the fact that when components used in the hot sections of gas turbine engines remain in service for ex- tended periods of time, the local temperature and stress provides the catalyst for the evolution of the microstructure. An experimental assessment of a negative misfit directionally solidified (DS) Ni- base superalloy was undertaken to characterize the aging kinetics and understand the influence of the TMF cycle temperature extremum, temperature-load phasing, mean strain, creep-fatigue, orientation effects, and microstructure on TMF fatigue crack initiation. To determine the effects of aging on the TMF response, the as-heat- treated alloy was artificially aged to three unique microstructures identified in the aging kinetics study. The experiments revealed that not all aged microstructures are detrimental to the fatigue life behavior. Specifically, when the γ′ precipitates age in a manner to align themselves parallel to the axis of the applied stress, an increase in the fatigue life over that of the as-heat-treated microstructure is observed for out-of-phase TMF with dwells. To extend the experimental understanding of the aged microstructures into ser- vice component design and life analysis, a temperature-dependent crystal viscoplas- ticity (CVP) constitutive model is developed to capture the sensitivity of the aged microstructure through embedding additional variables associated with the current state of the γ′ particles. As a result of the adaptations, the CVP model has the ability to describe the long-term aging effects of directional coarsening relevant to the analysis industrial gas turbine hot section components.
dc.format.mimetypeapplication/pdf
dc.publisherGeorgia Institute of Technology
dc.subjectAging
dc.subjectRafting
dc.subjectThermomechanical fatigue
dc.subjectNi-base superalloy
dc.subjectCrystal viscoplasticity
dc.subjectMicrostructure-sensitive modeling
dc.titleThermomechanical behavior of a directionally solidified nickel-base superalloys in the aged state
dc.typeDissertation
dc.description.degreePh.D.
dc.contributor.departmentMechanical Engineering
dc.embargo.terms2015-05-01
thesis.degree.levelDoctoral
dc.contributor.committeeMemberGerhardt, Rosario
dc.contributor.committeeMemberKalidindi, Surya
dc.contributor.committeeMemberMcDowell, David L.
dc.contributor.committeeMemberAntolovich, Stephen D.
dc.contributor.committeeMemberSanders, Thomas H.
dc.date.updated2015-06-08T18:15:17Z


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