{"id":{"repo_id":"calgary","oai_identifier":"oai:ucalgary.scholaris.ca:1880/124771"},"canonical_url":"https://search.dev.ndltd.org/etd/calgary/oai:ucalgary.scholaris.ca:1880/124771","repository":{"repo_id":"calgary","name":"University of Calgary","base_url":"https://ucalgary.scholaris.ca/server/oai/request"},"display":{"title":"From Functionally Graded to Grain-Boundary-Decorated Nanograined Alloys: a New Approach to Bulk Lightweight Alloy Design via Friction Stir Processing","abstract":"Lightweight structural materials offer an alternative strategy to combat global climate change. However, lightweighting often compromises material strength. This limitation can be mitigated by refining grains to ultrafine or nanocrystalline scales (<100 nm). Despite their advantages, the widespread use of refined-grain materials is limited by grain growth, even at ambient temperature, which degrades their mechanical and functional properties. Current thermodynamic grain boundary (GB) decoration approach for refined-grain stabilization is either limited to thin films or requires multi-step processes. Therefore, new processing routes are needed to produce stable refined-grain materials without these limitations. This Ph.D. thesis proposes friction stir processing (FSP) as a greener single-step method to produce bulk ultrafine/GB-decorated nanograined materials and enable the development of functionally graded materials (FGMs) through controlled processing parameters. A segregation map was developed for aluminum (a model FCC metal solvent) using empirical and enthalpic GB segregation criteria to identify suitable solute elements (magnesium and zinc) for GB segregation. The first binary system (Al–Mg) shows clear Mg segregation at the GBs of the Al-rich region near the Al–Mg interface, providing evidence of a one-step GB decoration process in bulk materials, beyond traditional thin-film and powder metallurgy approaches. For the Al–Zn system, a full factorial design of experiment (DOE) with regression modeling is employed to quantify the effects of processing parameters: rotational and traverse speeds, on peak temperature and groove length percentage. Following DOE analysis, further investigation of microstructural evolution, material flow behavior, defect formation, and mechanical response demonstrates the feasibility of the proposed FSP approach for developing FGMs. The results also reveal that the balance between “reinforcing” plate material distribution and complex microstructural evolution, including void closure and eutectic formation, plays a critical role in controlling the mechanical performance of sandwich structures. In addition, a novel finding that addresses whether continuous dynamic recrystallization (cDRX) can occur via an interrupted mechanism (icDRX) without extreme deformation or post-heat treatment is described in this thesis. These findings demonstrate that low strain/strain rate plastic deformation can induce grain refinement, offering potential pathways for improving material performance.","abstract_html":"Lightweight structural materials offer an alternative strategy to combat global climate change. However, lightweighting often compromises material strength. This limitation can be mitigated by refining grains to ultrafine or nanocrystalline scales (<100 nm). Despite their advantages, the widespread use of refined-grain materials is limited by grain growth, even at ambient temperature, which degrades their mechanical and functional properties. Current thermodynamic grain boundary (GB) decoration approach for refined-grain stabilization is either limited to thin films or requires multi-step processes. Therefore, new processing routes are needed to produce stable refined-grain materials without these limitations. This Ph.D. thesis proposes friction stir processing (FSP) as a greener single-step method to produce bulk ultrafine/GB-decorated nanograined materials and enable the development of functionally graded materials (FGMs) through controlled processing parameters. A segregation map was developed for aluminum (a model FCC metal solvent) using empirical and enthalpic GB segregation criteria to identify suitable solute elements (magnesium and zinc) for GB segregation. The first binary system (Al–Mg) shows clear Mg segregation at the GBs of the Al-rich region near the Al–Mg interface, providing evidence of a one-step GB decoration process in bulk materials, beyond traditional thin-film and powder metallurgy approaches. For the Al–Zn system, a full factorial design of experiment (DOE) with regression modeling is employed to quantify the effects of processing parameters: rotational and traverse speeds, on peak temperature and groove length percentage. Following DOE analysis, further investigation of microstructural evolution, material flow behavior, defect formation, and mechanical response demonstrates the feasibility of the proposed FSP approach for developing FGMs. The results also reveal that the balance between “reinforcing” plate material distribution and complex microstructural evolution, including void closure and eutectic formation, plays a critical role in controlling the mechanical performance of sandwich structures. In addition, a novel finding that addresses whether continuous dynamic recrystallization (cDRX) can occur via an interrupted mechanism (icDRX) without extreme deformation or post-heat treatment is described in this thesis. These findings demonstrate that low strain/strain rate plastic deformation can induce grain refinement, offering potential pathways for improving material performance.","abstract_has_math":false,"creators":["Dehghan, Mina"],"institution":"Schulich School of Engineering","degree_name":"Doctor of Philosophy (PhD)","degree_level":null,"degree_discipline":"Engineering – Mechanical & Manufacturing","degree_department":null,"school":null,"contributors":[],"advisors":["Tiamiyu, Ahmed"],"committee_chairs":[],"committee_members":["Kim, Keekyoung","Egberts, Philip"],"year":2026,"date_issued":"2026-04-30","date_published":"2026-04-30","updated_at":"2026-07-24T01:30:18Z","subjects":[],"languages":["en"],"rights":["Unless otherwise indicated, this material is protected by copyright and has been made available with authorization from the copyright owner. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission."],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier.doi","label":"DOI","values":["https://dx.doi.org/10.11575/PRISM/51379"],"render_values":[{"text":"https://dx.doi.org/10.11575/PRISM/51379","href":"https://dx.doi.org/10.11575/PRISM/51379","code":true}]}]},"links":{"outbound_url":"https://hdl.handle.net/1880/124771","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Tiamiyu, Ahmed"]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Kim, Keekyoung","Egberts, Philip"]},{"key":"dc:creator","label":"Author","values":["Dehghan, Mina"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2026-06"]},{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2026-05-04T15:06:46Z"]},{"key":"dc:date.issued","label":"Date","values":["2026-04-30"]},{"key":"dc:type","label":"Dc Type","values":["doctoral thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Engineering – Mechanical & Manufacturing"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy (PhD)"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Calgary"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["Unless otherwise indicated, this material is protected by copyright and has been made available with authorization from the copyright owner. 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Despite their advantages, the widespread use of refined-grain materials is limited by grain growth, even at ambient temperature, which degrades their mechanical and functional properties. Current thermodynamic grain boundary (GB) decoration approach for refined-grain stabilization is either limited to thin films or requires multi-step processes. Therefore, new processing routes are needed to produce stable refined-grain materials without these limitations. This Ph.D. thesis proposes friction stir processing (FSP) as a greener single-step method to produce bulk ultrafine/GB-decorated nanograined materials and enable the development of functionally graded materials (FGMs) through controlled processing parameters. A segregation map was developed for aluminum (a model FCC metal solvent) using empirical and enthalpic GB segregation criteria to identify suitable solute elements (magnesium and zinc) for GB segregation. The first binary system (Al–Mg) shows clear Mg segregation at the GBs of the Al-rich region near the Al–Mg interface, providing evidence of a one-step GB decoration process in bulk materials, beyond traditional thin-film and powder metallurgy approaches. For the Al–Zn system, a full factorial design of experiment (DOE) with regression modeling is employed to quantify the effects of processing parameters: rotational and traverse speeds, on peak temperature and groove length percentage. Following DOE analysis, further investigation of microstructural evolution, material flow behavior, defect formation, and mechanical response demonstrates the feasibility of the proposed FSP approach for developing FGMs. The results also reveal that the balance between “reinforcing” plate material distribution and complex microstructural evolution, including void closure and eutectic formation, plays a critical role in controlling the mechanical performance of sandwich structures. In addition, a novel finding that addresses whether continuous dynamic recrystallization (cDRX) can occur via an interrupted mechanism (icDRX) without extreme deformation or post-heat treatment is described in this thesis. These findings demonstrate that low strain/strain rate plastic deformation can induce grain refinement, offering potential pathways for improving material performance."]},{"key":"dc:title","label":"Title","values":["From Functionally Graded to Grain-Boundary-Decorated Nanograined Alloys: a New Approach to Bulk Lightweight Alloy Design via Friction Stir Processing"]}]}],"canonical_facts":{"dc:contributor.advisor":["Tiamiyu, Ahmed"],"dc:contributor.committeemember":["Kim, Keekyoung","Egberts, Philip"],"dc:creator":["Dehghan, Mina"],"dc:date":["2026-06"],"dc:date.accessioned":["2026-05-04T15:06:46Z"],"dc:date.issued":["2026-04-30"],"dc:description.abstract":["Lightweight structural materials offer an alternative strategy to combat global climate change. However, lightweighting often compromises material strength. This limitation can be mitigated by refining grains to ultrafine or nanocrystalline scales (<100 nm). Despite their advantages, the widespread use of refined-grain materials is limited by grain growth, even at ambient temperature, which degrades their mechanical and functional properties. Current thermodynamic grain boundary (GB) decoration approach for refined-grain stabilization is either limited to thin films or requires multi-step processes. Therefore, new processing routes are needed to produce stable refined-grain materials without these limitations. This Ph.D. thesis proposes friction stir processing (FSP) as a greener single-step method to produce bulk ultrafine/GB-decorated nanograined materials and enable the development of functionally graded materials (FGMs) through controlled processing parameters. A segregation map was developed for aluminum (a model FCC metal solvent) using empirical and enthalpic GB segregation criteria to identify suitable solute elements (magnesium and zinc) for GB segregation. The first binary system (Al–Mg) shows clear Mg segregation at the GBs of the Al-rich region near the Al–Mg interface, providing evidence of a one-step GB decoration process in bulk materials, beyond traditional thin-film and powder metallurgy approaches. For the Al–Zn system, a full factorial design of experiment (DOE) with regression modeling is employed to quantify the effects of processing parameters: rotational and traverse speeds, on peak temperature and groove length percentage. Following DOE analysis, further investigation of microstructural evolution, material flow behavior, defect formation, and mechanical response demonstrates the feasibility of the proposed FSP approach for developing FGMs. The results also reveal that the balance between “reinforcing” plate material distribution and complex microstructural evolution, including void closure and eutectic formation, plays a critical role in controlling the mechanical performance of sandwich structures. In addition, a novel finding that addresses whether continuous dynamic recrystallization (cDRX) can occur via an interrupted mechanism (icDRX) without extreme deformation or post-heat treatment is described in this thesis. These findings demonstrate that low strain/strain rate plastic deformation can induce grain refinement, offering potential pathways for improving material performance."],"dc:identifier.doi":["https://dx.doi.org/10.11575/PRISM/51379"],"dc:identifier.uri":["https://hdl.handle.net/1880/124771"],"dc:language.iso":["en"],"dc:rights":["Unless otherwise indicated, this material is protected by copyright and has been made available with authorization from the copyright owner. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission."],"dc:title":["From Functionally Graded to Grain-Boundary-Decorated Nanograined Alloys: a New Approach to Bulk Lightweight Alloy Design via Friction Stir Processing"],"dc:type":["doctoral thesis"],"thesis:degree_discipline":["Engineering – Mechanical & Manufacturing"],"thesis:degree_name":["Doctor of Philosophy (PhD)"],"thesis:institution_name":["University of Calgary"]},"updated_at":"2026-07-24T01:30:18Z"}