{"id":{"repo_id":"auckland-ms","oai_identifier":"oai:researchspace.auckland.ac.nz:2292/76102"},"canonical_url":"https://search.dev.ndltd.org/etd/auckland-ms/oai:researchspace.auckland.ac.nz:2292/76102","repository":{"repo_id":"auckland-ms","name":"University of Auckland","base_url":"https://researchspace.auckland.ac.nz/server/oai/request"},"display":{"title":"In Situ Alloying of Titanium via Laser Powder Bed Fusion","abstract":"Laser powder bed fusion is a leading additive manufacturing technique capable of producing complex, customised titanium components. However, its broader adoption is constrained by limited commercial alloy options, the high cost of pre-alloyed powders, and pronounced anisotropy arising from coarse columnar grain growth. This thesis addresses these challenges through in-situ alloying strategies that use mixed elemental or composite feedstocks to enable novel Ti-based alloy development directly during LPBF processing. The first stage of this work investigates a binary Ti–2.9Cu alloy fabricated from blended Ti and Cu powders. An optimal process window was established, yielding near-fully dense, crack-free samples. The as-built alloy comprised α-laths with nano-sized Ti₂Cu precipitates and eutectoid lamellae. Mechanical properties showed a strength–ductility trade-off influenced by volumetric energy density and heat treatment pathways, highlighting the limitations of simple powder blends. To overcome this trade-off, a core–shell Ti@Cu feedstock was developed. The engineered powders achieved uniform Cu distribution and resulted in a fully equiaxed prior-β grain structure, ultra-fine α laths, and homogeneously dispersed nano-Ti₂Cu. Compared with the blended alloy, the core–shell system exhibited simultaneous improvements in strength and ductility. Melt-pool simulations revealed that the core–shell architecture promotes stable, symmetric thermal behaviour and suppresses solute segregation, leading to enhanced compositional uniformity. Post-processing heat treatments demonstrated that precipitation hardening in the core–shell alloy is strongly influenced by β→α partitioning, with ageing at 500 °C for 4 h providing the optimal balance between strength and ductility. The final component of this thesis extends in-situ alloying to a multi-component system by combining elemental Ti with pre-alloyed SS316L powder. The resulting Ti–6SS alloy exhibited controlled compositional gradients, forming a β-stabilised shell and α′-martensitic core. This heterostructure achieved high strength with good ductility. The enhanced mechanical response was attributed to heterostructure strengthening and localised high-density inclusion stress distribution. Overall, this thesis establishes a scalable, feedstock-driven framework for designing new Ti-based alloys via LPBF. By integrating powder engineering, process optimisation, and targeted heat treatments, this work demonstrates how in-situ alloying can overcome key limitations of conventional AM feedstocks and enable tailored microstructures for advanced biomedical and structural applications.","abstract_html":"Laser powder bed fusion is a leading additive manufacturing technique capable of producing complex, customised titanium components. However, its broader adoption is constrained by limited commercial alloy options, the high cost of pre-alloyed powders, and pronounced anisotropy arising from coarse columnar grain growth. This thesis addresses these challenges through in-situ alloying strategies that use mixed elemental or composite feedstocks to enable novel Ti-based alloy development directly during LPBF processing. The first stage of this work investigates a binary Ti–2.9Cu alloy fabricated from blended Ti and Cu powders. An optimal process window was established, yielding near-fully dense, crack-free samples. The as-built alloy comprised α-laths with nano-sized Ti₂Cu precipitates and eutectoid lamellae. Mechanical properties showed a strength–ductility trade-off influenced by volumetric energy density and heat treatment pathways, highlighting the limitations of simple powder blends. To overcome this trade-off, a core–shell Ti@Cu feedstock was developed. The engineered powders achieved uniform Cu distribution and resulted in a fully equiaxed prior-β grain structure, ultra-fine α laths, and homogeneously dispersed nano-Ti₂Cu. Compared with the blended alloy, the core–shell system exhibited simultaneous improvements in strength and ductility. Melt-pool simulations revealed that the core–shell architecture promotes stable, symmetric thermal behaviour and suppresses solute segregation, leading to enhanced compositional uniformity. Post-processing heat treatments demonstrated that precipitation hardening in the core–shell alloy is strongly influenced by β→α partitioning, with ageing at 500 °C for 4 h providing the optimal balance between strength and ductility. The final component of this thesis extends in-situ alloying to a multi-component system by combining elemental Ti with pre-alloyed SS316L powder. The resulting Ti–6SS alloy exhibited controlled compositional gradients, forming a β-stabilised shell and α′-martensitic core. This heterostructure achieved high strength with good ductility. The enhanced mechanical response was attributed to heterostructure strengthening and localised high-density inclusion stress distribution. Overall, this thesis establishes a scalable, feedstock-driven framework for designing new Ti-based alloys via LPBF. By integrating powder engineering, process optimisation, and targeted heat treatments, this work demonstrates how in-situ alloying can overcome key limitations of conventional AM feedstocks and enable tailored microstructures for advanced biomedical and structural applications.","abstract_has_math":false,"creators":["Xu, Dingmeng"],"institution":"ResearchSpace@Auckland","degree_name":"PhD","degree_level":"Doctoral","degree_discipline":"Chemical and Materials Engineering","degree_department":null,"school":null,"contributors":[],"advisors":["Cao, Peng","Hodgson, Michael"],"committee_chairs":[],"committee_members":[],"year":2025,"date_issued":"2025","date_published":"2025","updated_at":"2026-07-24T01:05:11Z","subjects":["Additive Manufacturing","Titanium","Laser Powder Bed Fusion"],"languages":[],"rights":["Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated."],"rights_urls":["https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm"],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/2292/76102","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Cao, Peng","Hodgson, Michael"]},{"key":"dc:creator","label":"Author","values":["Xu, Dingmeng"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2026-06-22T00:56:11Z"]},{"key":"dc:date.issued","label":"Date","values":["2025"]},{"key":"dc:publisher","label":"Institution","values":["ResearchSpace@Auckland"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Chemical and Materials Engineering"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Doctoral"]},{"key":"thesis:degree_name","label":"Degree Name","values":["PhD"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["The University of Auckland"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Additive Manufacturing","Titanium","Laser Powder Bed Fusion"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:rights","label":"Dc Rights","values":["Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated."]},{"key":"dc:rights.uri","label":"Rights URI","values":["https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/2292/76102"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Laser powder bed fusion is a leading additive manufacturing technique capable of producing complex, customised titanium components. However, its broader adoption is constrained by limited commercial alloy options, the high cost of pre-alloyed powders, and pronounced anisotropy arising from coarse columnar grain growth. This thesis addresses these challenges through in-situ alloying strategies that use mixed elemental or composite feedstocks to enable novel Ti-based alloy development directly during LPBF processing. The first stage of this work investigates a binary Ti–2.9Cu alloy fabricated from blended Ti and Cu powders. An optimal process window was established, yielding near-fully dense, crack-free samples. The as-built alloy comprised α-laths with nano-sized Ti₂Cu precipitates and eutectoid lamellae. Mechanical properties showed a strength–ductility trade-off influenced by volumetric energy density and heat treatment pathways, highlighting the limitations of simple powder blends. To overcome this trade-off, a core–shell Ti@Cu feedstock was developed. The engineered powders achieved uniform Cu distribution and resulted in a fully equiaxed prior-β grain structure, ultra-fine α laths, and homogeneously dispersed nano-Ti₂Cu. Compared with the blended alloy, the core–shell system exhibited simultaneous improvements in strength and ductility. Melt-pool simulations revealed that the core–shell architecture promotes stable, symmetric thermal behaviour and suppresses solute segregation, leading to enhanced compositional uniformity. Post-processing heat treatments demonstrated that precipitation hardening in the core–shell alloy is strongly influenced by β→α partitioning, with ageing at 500 °C for 4 h providing the optimal balance between strength and ductility. The final component of this thesis extends in-situ alloying to a multi-component system by combining elemental Ti with pre-alloyed SS316L powder. The resulting Ti–6SS alloy exhibited controlled compositional gradients, forming a β-stabilised shell and α′-martensitic core. This heterostructure achieved high strength with good ductility. The enhanced mechanical response was attributed to heterostructure strengthening and localised high-density inclusion stress distribution. Overall, this thesis establishes a scalable, feedstock-driven framework for designing new Ti-based alloys via LPBF. By integrating powder engineering, process optimisation, and targeted heat treatments, this work demonstrates how in-situ alloying can overcome key limitations of conventional AM feedstocks and enable tailored microstructures for advanced biomedical and structural applications."]},{"key":"dc:title","label":"Title","values":["In Situ Alloying of Titanium via Laser Powder Bed Fusion"]}]}],"canonical_facts":{"dc:contributor.advisor":["Cao, Peng","Hodgson, Michael"],"dc:creator":["Xu, Dingmeng"],"dc:date.accessioned":["2026-06-22T00:56:11Z"],"dc:date.issued":["2025"],"dc:description.abstract":["Laser powder bed fusion is a leading additive manufacturing technique capable of producing complex, customised titanium components. However, its broader adoption is constrained by limited commercial alloy options, the high cost of pre-alloyed powders, and pronounced anisotropy arising from coarse columnar grain growth. This thesis addresses these challenges through in-situ alloying strategies that use mixed elemental or composite feedstocks to enable novel Ti-based alloy development directly during LPBF processing. The first stage of this work investigates a binary Ti–2.9Cu alloy fabricated from blended Ti and Cu powders. An optimal process window was established, yielding near-fully dense, crack-free samples. The as-built alloy comprised α-laths with nano-sized Ti₂Cu precipitates and eutectoid lamellae. Mechanical properties showed a strength–ductility trade-off influenced by volumetric energy density and heat treatment pathways, highlighting the limitations of simple powder blends. To overcome this trade-off, a core–shell Ti@Cu feedstock was developed. The engineered powders achieved uniform Cu distribution and resulted in a fully equiaxed prior-β grain structure, ultra-fine α laths, and homogeneously dispersed nano-Ti₂Cu. Compared with the blended alloy, the core–shell system exhibited simultaneous improvements in strength and ductility. Melt-pool simulations revealed that the core–shell architecture promotes stable, symmetric thermal behaviour and suppresses solute segregation, leading to enhanced compositional uniformity. Post-processing heat treatments demonstrated that precipitation hardening in the core–shell alloy is strongly influenced by β→α partitioning, with ageing at 500 °C for 4 h providing the optimal balance between strength and ductility. The final component of this thesis extends in-situ alloying to a multi-component system by combining elemental Ti with pre-alloyed SS316L powder. The resulting Ti–6SS alloy exhibited controlled compositional gradients, forming a β-stabilised shell and α′-martensitic core. This heterostructure achieved high strength with good ductility. The enhanced mechanical response was attributed to heterostructure strengthening and localised high-density inclusion stress distribution. Overall, this thesis establishes a scalable, feedstock-driven framework for designing new Ti-based alloys via LPBF. By integrating powder engineering, process optimisation, and targeted heat treatments, this work demonstrates how in-situ alloying can overcome key limitations of conventional AM feedstocks and enable tailored microstructures for advanced biomedical and structural applications."],"dc:identifier.uri":["https://hdl.handle.net/2292/76102"],"dc:publisher":["ResearchSpace@Auckland"],"dc:rights":["Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated."],"dc:rights.uri":["https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm"],"dc:subject":["Additive Manufacturing","Titanium","Laser Powder Bed Fusion"],"dc:title":["In Situ Alloying of Titanium via Laser Powder Bed Fusion"],"dc:type":["Thesis"],"thesis:degree_discipline":["Chemical and Materials Engineering"],"thesis:degree_level":["Doctoral"],"thesis:degree_name":["PhD"],"thesis:institution_name":["The University of Auckland"]},"updated_at":"2026-07-24T01:05:11Z"}