{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/71701"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/71701","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Fracture of Hot-Pressed Silicon Nitride at Elevated Temperatures","abstract":"MgO-doped and Al(,2)O(,3)-Y(,2)O(,3)-doped hot-pressed silicon nitrides were fractured between 1100(DEGREES)C and 1350(DEGREES)C in four point bend at three displacement rates. Fracture stress and critical stress intensity factor were calculated and plotted versus temperature for each displacement rate. The scanning electron microscope, transmission electron microscope and scanning Auger electron spectrometer were used to analyze as-received and fractured material. Fracture stress and critical stress intensity factor showed a strain rate dependence above 1200(DEGREES)C. The MgO-doped Si(,3)N(,4) exhibited a peak in fracture stress before the values decreased at high temperatures. This peak corresponds to the onset of subcritical crack growth prior to catastrophic failure. Subcritical cracking is believed to occur by the nucleation, growth and coalescence of cavities in the secondary, amorphous grain boundary phase. The coalescence of cavities along with grain boundary separation results in the formation of microcracks in the vicinity of the main crack. The main crack then advances slowly by joining up with these nearby microcracks. Cavities and regions of grain boundary deformation were observed with SEM and TEM. A map was drawn of displacement rate versus temperature showing regions where subcritical cracking was and was not observed as well as a transition region. Both silicon nitrides exhibited a peak in effective critical stress intensity factor prior to the decrease. A decrease in K(,1C) results as the material weakens at high temperatures. The Y(,2)O(,3)-Al(,2)O(,3)-doped silicon nitride sustained its strength and K(,1C) to higher temperatures due to its more refractory Y(,2)O(,3)-Al(,2)O(,3)-SiO(,2) crystalline compound grain boundary phase than the amorphous magnesium-silicate phase present in the MgO-doped silicon nitride.","abstract_html":"MgO-doped and Al(,2)O(,3)-Y(,2)O(,3)-doped hot-pressed silicon nitrides were fractured between 1100(DEGREES)C and 1350(DEGREES)C in four point bend at three displacement rates. Fracture stress and critical stress intensity factor were calculated and plotted versus temperature for each displacement rate. The scanning electron microscope, transmission electron microscope and scanning Auger electron spectrometer were used to analyze as-received and fractured material. Fracture stress and critical stress intensity factor showed a strain rate dependence above 1200(DEGREES)C. The MgO-doped Si(,3)N(,4) exhibited a peak in fracture stress before the values decreased at high temperatures. This peak corresponds to the onset of subcritical crack growth prior to catastrophic failure. Subcritical cracking is believed to occur by the nucleation, growth and coalescence of cavities in the secondary, amorphous grain boundary phase. The coalescence of cavities along with grain boundary separation results in the formation of microcracks in the vicinity of the main crack. The main crack then advances slowly by joining up with these nearby microcracks. Cavities and regions of grain boundary deformation were observed with SEM and TEM. A map was drawn of displacement rate versus temperature showing regions where subcritical cracking was and was not observed as well as a transition region. Both silicon nitrides exhibited a peak in effective critical stress intensity factor prior to the decrease. A decrease in K(,1C) results as the material weakens at high temperatures. The Y(,2)O(,3)-Al(,2)O(,3)-doped silicon nitride sustained its strength and K(,1C) to higher temperatures due to its more refractory Y(,2)O(,3)-Al(,2)O(,3)-SiO(,2) crystalline compound grain boundary phase than the amorphous magnesium-silicate phase present in the MgO-doped silicon nitride.","abstract_has_math":false,"creators":["Knickerbocker, Sarah Huffsmith"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Ceramics Engineering","degree_department":null,"school":null,"contributors":[],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2014,"date_issued":"2014-12-16T19:16:55Z","date_published":"2014-12-16T19:16:55Z","updated_at":"2026-07-22T22:26:05Z","subjects":["Engineering, Chemical"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["(UMI)AAI8309969"],"render_values":[{"text":"(UMI)AAI8309969","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/2142/71701","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:creator","label":"Author","values":["Knickerbocker, Sarah Huffsmith"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2014-12-16T19:16:55Z","10000-01-01","1983"]},{"key":"dc:type","label":"Dc Type","values":["text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Ceramics Engineering"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Engineering, Chemical"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/71701","(UMI)AAI8309969"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["MgO-doped and Al(,2)O(,3)-Y(,2)O(,3)-doped hot-pressed silicon nitrides were fractured between 1100(DEGREES)C and 1350(DEGREES)C in four point bend at three displacement rates. Fracture stress and critical stress intensity factor were calculated and plotted versus temperature for each displacement rate. The scanning electron microscope, transmission electron microscope and scanning Auger electron spectrometer were used to analyze as-received and fractured material. Fracture stress and critical stress intensity factor showed a strain rate dependence above 1200(DEGREES)C. The MgO-doped Si(,3)N(,4) exhibited a peak in fracture stress before the values decreased at high temperatures. This peak corresponds to the onset of subcritical crack growth prior to catastrophic failure. Subcritical cracking is believed to occur by the nucleation, growth and coalescence of cavities in the secondary, amorphous grain boundary phase. The coalescence of cavities along with grain boundary separation results in the formation of microcracks in the vicinity of the main crack. The main crack then advances slowly by joining up with these nearby microcracks. Cavities and regions of grain boundary deformation were observed with SEM and TEM. A map was drawn of displacement rate versus temperature showing regions where subcritical cracking was and was not observed as well as a transition region. Both silicon nitrides exhibited a peak in effective critical stress intensity factor prior to the decrease. A decrease in K(,1C) results as the material weakens at high temperatures. The Y(,2)O(,3)-Al(,2)O(,3)-doped silicon nitride sustained its strength and K(,1C) to higher temperatures due to its more refractory Y(,2)O(,3)-Al(,2)O(,3)-SiO(,2) crystalline compound grain boundary phase than the amorphous magnesium-silicate phase present in the MgO-doped silicon nitride.","Made available in DSpace on 2014-12-16T19:16:55Z (GMT). No. of bitstreams: 1 8309969.pdf: 8789363 bytes, checksum: 5c0188eac88fcbd641a78f9e92dff846 (MD5) Previous issue date: 1983","Embargo set by: Seth Robbins for item 71867 Lift date: Forever Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs","Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs","U of I Only","306 p.","Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983."]},{"key":"dc:title","label":"Title","values":["Fracture of Hot-Pressed Silicon Nitride at Elevated Temperatures"]}]}],"canonical_facts":{"dc:creator":["Knickerbocker, Sarah Huffsmith"],"dc:date":["2014-12-16T19:16:55Z","10000-01-01","1983"],"dc:description":["MgO-doped and Al(,2)O(,3)-Y(,2)O(,3)-doped hot-pressed silicon nitrides were fractured between 1100(DEGREES)C and 1350(DEGREES)C in four point bend at three displacement rates. Fracture stress and critical stress intensity factor were calculated and plotted versus temperature for each displacement rate. The scanning electron microscope, transmission electron microscope and scanning Auger electron spectrometer were used to analyze as-received and fractured material. Fracture stress and critical stress intensity factor showed a strain rate dependence above 1200(DEGREES)C. The MgO-doped Si(,3)N(,4) exhibited a peak in fracture stress before the values decreased at high temperatures. This peak corresponds to the onset of subcritical crack growth prior to catastrophic failure. Subcritical cracking is believed to occur by the nucleation, growth and coalescence of cavities in the secondary, amorphous grain boundary phase. The coalescence of cavities along with grain boundary separation results in the formation of microcracks in the vicinity of the main crack. The main crack then advances slowly by joining up with these nearby microcracks. Cavities and regions of grain boundary deformation were observed with SEM and TEM. A map was drawn of displacement rate versus temperature showing regions where subcritical cracking was and was not observed as well as a transition region. Both silicon nitrides exhibited a peak in effective critical stress intensity factor prior to the decrease. A decrease in K(,1C) results as the material weakens at high temperatures. The Y(,2)O(,3)-Al(,2)O(,3)-doped silicon nitride sustained its strength and K(,1C) to higher temperatures due to its more refractory Y(,2)O(,3)-Al(,2)O(,3)-SiO(,2) crystalline compound grain boundary phase than the amorphous magnesium-silicate phase present in the MgO-doped silicon nitride.","Made available in DSpace on 2014-12-16T19:16:55Z (GMT). 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