{"id":{"repo_id":"manitoba","oai_identifier":"oai:mspace.lib.umanitoba.ca:1993/932"},"canonical_url":"https://search.dev.ndltd.org/etd/manitoba/oai:mspace.lib.umanitoba.ca:1993/932","repository":{"repo_id":"manitoba","name":"University of Manitoba","base_url":"https://mspace.lib.umanitoba.ca/oai/request"},"display":{"title":"Microstructural responses of a nickel-base cast IN-738 superalloy to a variety of pre-weld heat-treatments","abstract":"This dissertation reports an investigation involving a thorough characterization of the microstructural response of cast IN-738 to a variety of pre-weld heat-treatment schemes. The as-received material showed cored dendritic microstructure, containing coarse grains, about 0.5% casting micropores, 0.7% primary carbide particles, and 42% primary $\\gamma\\prime$ particles respectively. The volume-fraction of primary $\\gamma\\prime$ particles decreased continuously from 20.1% to about 5% for solution-treatment temperatures (STT) in the range of 1120$\\sp\\circ$C-1225$\\sp\\circ$C. The solvus of primary $\\gamma\\prime$ particles was higher than the 1160$\\sp\\circ$C-1175$\\sp\\circ$C range suggested by Steven and Flewitt (27). The brine-quenched samples from the STT manifested extensive intergranular cracking and aging contraction stresses. Aging resulted in coarsening of primary and secondary $\\gamma\\prime$ particles, degeneration and dissociation of primary carbide particles to form secondary $\\gamma\\prime$ particles andfine $\\rm M\\sb{23}C\\sb6$ carbide particles on the grain-boundaries. Only long-term aging showed the presence of these secondary carbide particles in the grain interiors. Aging at 845$\\sp\\circ$C, after solution-treating at 1120$\\sp\\circ$C showed a distinct bimodal distribution of $\\gamma\\prime$ particles. The overaged microstructure for the 1175$\\sp\\circ$C and 1225$\\sp\\circ$C consisted of a unimodal distribution of degenerate $\\gamma\\prime$ particles. The activation energy for the coarsening of secondary $\\gamma\\prime$ particles using the LSEM theory was 241 KJ/molK, in reasonable agreement with the 259KJ/molK calculated by Henderson et. al. (45). Grain-boundary $\\rm M\\sb{23}C\\sb6$ carbide particles have a solvus of about 1025$\\sp\\circ$C and liquate/dissolve at higher temperatures. The liquation of low-melting continuously linked fine carbide particles on the boundaries was another sole cause for intergranular quench cracks. The coherency strains are usually responsible for heat-affected zone microfissuring in this material and were found to be always lower for the overaged material as compared to the peak-aged and the underaged material. (Abstract shortened by UMI.)","abstract_html":"This dissertation reports an investigation involving a thorough characterization of the microstructural response of cast IN-738 to a variety of pre-weld heat-treatment schemes. The as-received material showed cored dendritic microstructure, containing coarse grains, about 0.5% casting micropores, 0.7% primary carbide particles, and 42% primary <span class=\"etd-inline-math\">&gamma;\\prime</span> particles respectively. The volume-fraction of primary <span class=\"etd-inline-math\">&gamma;\\prime</span> particles decreased continuously from 20.1% to about 5% for solution-treatment temperatures (STT) in the range of 1120$\\sp\\circ$C-1225$\\sp\\circ$C. The solvus of primary <span class=\"etd-inline-math\">&gamma;\\prime</span> particles was higher than the 1160$\\sp\\circ$C-1175$\\sp\\circ$C range suggested by Steven and Flewitt (27). The brine-quenched samples from the STT manifested extensive intergranular cracking and aging contraction stresses. Aging resulted in coarsening of primary and secondary <span class=\"etd-inline-math\">&gamma;\\prime</span> particles, degeneration and dissociation of primary carbide particles to form secondary <span class=\"etd-inline-math\">&gamma;\\prime</span> particles andfine $\\rm M\\sb{23}C\\sb6$ carbide particles on the grain-boundaries. Only long-term aging showed the presence of these secondary carbide particles in the grain interiors. Aging at 845$\\sp\\circ$C, after solution-treating at 1120$\\sp\\circ$C showed a distinct bimodal distribution of <span class=\"etd-inline-math\">&gamma;\\prime</span> particles. The overaged microstructure for the 1175$\\sp\\circ$C and 1225$\\sp\\circ$C consisted of a unimodal distribution of degenerate <span class=\"etd-inline-math\">&gamma;\\prime</span> particles. The activation energy for the coarsening of secondary <span class=\"etd-inline-math\">&gamma;\\prime</span> particles using the LSEM theory was 241 KJ/molK, in reasonable agreement with the 259KJ/molK calculated by Henderson et. al. (45). Grain-boundary $\\rm M\\sb{23}C\\sb6$ carbide particles have a solvus of about 1025$\\sp\\circ$C and liquate/dissolve at higher temperatures. The liquation of low-melting continuously linked fine carbide particles on the boundaries was another sole cause for intergranular quench cracks. The coherency strains are usually responsible for heat-affected zone microfissuring in this material and were found to be always lower for the overaged material as compared to the peak-aged and the underaged material. (Abstract shortened by UMI.)","abstract_has_math":true,"creators":["Thakur, Anurag"],"institution":null,"degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":[],"committee_chairs":[],"committee_members":[],"year":1997,"date_issued":"1997-09-01T00:00:00Z","date_published":"1997-09-01T00:00:00Z","updated_at":"2026-07-24T03:02:01Z","subjects":[],"languages":["eng"],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/1993/932","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:creator","label":"Author","values":["Thakur, Anurag"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2007-05-15T15:21:44Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2007-05-15T15:21:44Z"]},{"key":"dc:date.issued","label":"Date","values":["1997-09-01T00:00:00Z"]},{"key":"dc:type","label":"Dc Type","values":["master thesis"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["eng"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/1993/932"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["This dissertation reports an investigation involving a thorough characterization of the microstructural response of cast IN-738 to a variety of pre-weld heat-treatment schemes. The as-received material showed cored dendritic microstructure, containing coarse grains, about 0.5% casting micropores, 0.7% primary carbide particles, and 42% primary $\\gamma\\prime$ particles respectively. The volume-fraction of primary $\\gamma\\prime$ particles decreased continuously from 20.1% to about 5% for solution-treatment temperatures (STT) in the range of 1120$\\sp\\circ$C-1225$\\sp\\circ$C. The solvus of primary $\\gamma\\prime$ particles was higher than the 1160$\\sp\\circ$C-1175$\\sp\\circ$C range suggested by Steven and Flewitt (27). The brine-quenched samples from the STT manifested extensive intergranular cracking and aging contraction stresses. Aging resulted in coarsening of primary and secondary $\\gamma\\prime$ particles, degeneration and dissociation of primary carbide particles to form secondary $\\gamma\\prime$ particles andfine $\\rm M\\sb{23}C\\sb6$ carbide particles on the grain-boundaries. Only long-term aging showed the presence of these secondary carbide particles in the grain interiors. Aging at 845$\\sp\\circ$C, after solution-treating at 1120$\\sp\\circ$C showed a distinct bimodal distribution of $\\gamma\\prime$ particles. The overaged microstructure for the 1175$\\sp\\circ$C and 1225$\\sp\\circ$C consisted of a unimodal distribution of degenerate $\\gamma\\prime$ particles. The activation energy for the coarsening of secondary $\\gamma\\prime$ particles using the LSEM theory was 241 KJ/molK, in reasonable agreement with the 259KJ/molK calculated by Henderson et. al. (45). Grain-boundary $\\rm M\\sb{23}C\\sb6$ carbide particles have a solvus of about 1025$\\sp\\circ$C and liquate/dissolve at higher temperatures. The liquation of low-melting continuously linked fine carbide particles on the boundaries was another sole cause for intergranular quench cracks. The coherency strains are usually responsible for heat-affected zone microfissuring in this material and were found to be always lower for the overaged material as compared to the peak-aged and the underaged material. (Abstract shortened by UMI.)"]},{"key":"dc:format.mimetype","label":"Dc Format Mimetype","values":["application/pdf","text/plain"]},{"key":"dc:title","label":"Title","values":["Microstructural responses of a nickel-base cast IN-738 superalloy to a variety of pre-weld heat-treatments"]}]}],"canonical_facts":{"dc:creator":["Thakur, Anurag"],"dc:date.accessioned":["2007-05-15T15:21:44Z"],"dc:date.available":["2007-05-15T15:21:44Z"],"dc:date.issued":["1997-09-01T00:00:00Z"],"dc:description.abstract":["This dissertation reports an investigation involving a thorough characterization of the microstructural response of cast IN-738 to a variety of pre-weld heat-treatment schemes. The as-received material showed cored dendritic microstructure, containing coarse grains, about 0.5% casting micropores, 0.7% primary carbide particles, and 42% primary $\\gamma\\prime$ particles respectively. The volume-fraction of primary $\\gamma\\prime$ particles decreased continuously from 20.1% to about 5% for solution-treatment temperatures (STT) in the range of 1120$\\sp\\circ$C-1225$\\sp\\circ$C. The solvus of primary $\\gamma\\prime$ particles was higher than the 1160$\\sp\\circ$C-1175$\\sp\\circ$C range suggested by Steven and Flewitt (27). The brine-quenched samples from the STT manifested extensive intergranular cracking and aging contraction stresses. Aging resulted in coarsening of primary and secondary $\\gamma\\prime$ particles, degeneration and dissociation of primary carbide particles to form secondary $\\gamma\\prime$ particles andfine $\\rm M\\sb{23}C\\sb6$ carbide particles on the grain-boundaries. Only long-term aging showed the presence of these secondary carbide particles in the grain interiors. Aging at 845$\\sp\\circ$C, after solution-treating at 1120$\\sp\\circ$C showed a distinct bimodal distribution of $\\gamma\\prime$ particles. The overaged microstructure for the 1175$\\sp\\circ$C and 1225$\\sp\\circ$C consisted of a unimodal distribution of degenerate $\\gamma\\prime$ particles. The activation energy for the coarsening of secondary $\\gamma\\prime$ particles using the LSEM theory was 241 KJ/molK, in reasonable agreement with the 259KJ/molK calculated by Henderson et. al. (45). Grain-boundary $\\rm M\\sb{23}C\\sb6$ carbide particles have a solvus of about 1025$\\sp\\circ$C and liquate/dissolve at higher temperatures. The liquation of low-melting continuously linked fine carbide particles on the boundaries was another sole cause for intergranular quench cracks. The coherency strains are usually responsible for heat-affected zone microfissuring in this material and were found to be always lower for the overaged material as compared to the peak-aged and the underaged material. (Abstract shortened by UMI.)"],"dc:format.mimetype":["application/pdf","text/plain"],"dc:identifier.uri":["http://hdl.handle.net/1993/932"],"dc:language.iso":["eng"],"dc:title":["Microstructural responses of a nickel-base cast IN-738 superalloy to a variety of pre-weld heat-treatments"],"dc:type":["master thesis"]},"updated_at":"2026-07-24T03:02:01Z"}