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dc.contributor.advisorJayaram, Vikram
dc.contributor.advisorAlam, Zafir
dc.contributor.authorKumawat, Mahesh Kumar
dc.date.accessioned2024-02-12T09:02:48Z
dc.date.available2024-02-12T09:02:48Z
dc.date.submitted2023
dc.identifier.urihttps://etd.iisc.ac.in/handle/2005/6409
dc.description.abstractPt-aluminide (PtAl) bond coat is used as a part of Thermal Barrier Coating (TBC) system on Ni-base superalloy components in advanced gas turbine aeroengines. The thickness of B2-NiAl intermetallic based diffused coating varies in the range of 60-100 µm. The coating provides excellent protection against oxidation to the superalloy components experiencing extreme temperatures of 1000°C during the operation of aeroengine. High temperatures combined with fluctuating mechanical loads can induce fatigue damage in the coating during service. Damage initiated in diffused coating propagates into the superalloy substrate and causes failure of the components. Therefore, evaluation of micro-mechanical properties of the PtAl bond coat is essential from the scientific and engineering application standpoints. The present study evaluates fatigue behavior of freestanding PtAl coating in the temperature range of ambient to 1000°C. Testing of the coating in freestanding form provides scientific understanding of inherent fatigue behavior and the evolution of fatigue damage in the coating without any influence from the substrate. Detailed microstructural characterization of the fatigue tested coating microsamples using SEM-EBSD, XRM and TEM has been carried out to ascertain the fatigue damage mechanisms in the coating. The fatigue behavior of the coating can be categorized into two temperature regimes, i.e., ambient to 800°C and above 900°C. In the temperature regime of ambient to 800°C, high dislocation activity, formation of dislocation cells and dislocation-precipitate interactions induce strain hardening are observed in the coating. The failure of the coating in the ambient to 800°C range is caused by the formation of micro-voids due to de-cohesion of precipitate/B2-matrix interface in the heavily precipitated interdiffusion zone, subsequent formation of micro-cracks by coalescence of micro-voids, and final failure by propagation of micro-cracks. Fatigue tested samples above 900°C exhibit extensive voiding preferentially in the outer layer of the coating. The role of dynamic recrystallization in the transition of the preferential layer for fatigue damage initiation with the increase in temperature is ascertained. The formation of voids above 900°C results from the creep damage in the coating. Cyclic loading leads to the formation of microcracks from these voids, and final failure is caused by the propagation of cracks. Deflection of crack and blunting of the crack tip govern the resistance to the propagation of cracks.en_US
dc.language.isoen_USen_US
dc.relation.ispartofseries;ET00421
dc.rightsI grant Indian Institute of Science the right to archive and to make available my thesis or dissertation in whole or in part in all forms of media, now hereafter known. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertationen_US
dc.subjectThermal Barrier Coatingen_US
dc.subjectBond Coaten_US
dc.subjectPlatinum-aluminide bond coaten_US
dc.subjectNickel super alloyen_US
dc.subjectSuper alloyen_US
dc.subjectmicrocracksen_US
dc.subjectmicrostructural characterizationen_US
dc.subject.classificationResearch Subject Categories::TECHNOLOGY::Materials science::Surface engineeringen_US
dc.titleUniaxial Fatigue Behavior of Freestanding Platinum-Aluminide (PtAl) Bond Coaten_US
dc.typeThesisen_US
dc.degree.namePhDen_US
dc.degree.levelDoctoralen_US
dc.degree.grantorIndian Institute of Scienceen_US
dc.degree.disciplineEngineeringen_US


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