Microstructural studies on failure mechanisms in thermo-mechanical fatigue of repaired DS R80 and IN738 Superalloys

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dc.contributor.authorAbrokwah, Emmanuel
dc.contributor.examiningcommitteeOjo, Olanrewaju (Mechanical and Manufacturing Engineering) Filizadeh, Shaahin (Electrical and Computer Engineering)en_US
dc.contributor.supervisorRichards, Norman(Mechanical and Manufacturing Engineering)en_US
dc.date.accessioned2012-03-16T19:45:20Z
dc.date.available2012-03-16T19:45:20Z
dc.date.issued2012-03-16
dc.degree.disciplineMechanical and Manufacturing Engineeringen_US
dc.degree.levelMaster of Science (M.Sc.)en_US
dc.description.abstractDirectionally solidified Rene 80 (DS R80) and polycrystalline Inconel 738(IN 738) Superalloys were tested in thermo-mechanical fatigue (TMF) over the temperature range of 500-900°C and plastic strain range from 0.1 to 0.8% using a DSI Gleeble thermal simulator. Thermo-mechanical testing was carried out on the parent material (baseline) in the conventional solution treated and aged condition (STA), as well as gas tungsten arc welded (GTAW) with an IN-738 filler, followed by solution treatment and ageing. Comparison of the baseline alloy microstructure with that of the welded and heat treated alloy showed that varying crack initiation mechanisms, notably oxidation by stress assisted grain boundary oxidation, grain boundary MC carbides fatigue crack initiation, fatigue crack initiation from sample surfaces, crack initiation from weld defects and creep deformation were operating, leading to different “weakest link” and failure initiation points. The observations from this study show that the repaired samples had extra crack initiation sites not present in the baseline, which accounted for their occasional poor fatigue life. These defects include lack of fusion between the weld and the base metal, fusion zone cracking, and heat affected zone microfissures.en_US
dc.description.noteMay 2012en_US
dc.identifier.urihttp://hdl.handle.net/1993/5195
dc.language.isoengen_US
dc.rightsopen accessen_US
dc.subjectNi base superalloysen_US
dc.subjectWeld repairen_US
dc.subjectThermo-mechanical fatigueen_US
dc.subjectFailure analysisen_US
dc.subjectGleeble simulationen_US
dc.titleMicrostructural studies on failure mechanisms in thermo-mechanical fatigue of repaired DS R80 and IN738 Superalloysen_US
dc.typemaster thesisen_US
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