In Situ Alloying of Titanium via Laser Powder Bed Fusion

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.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Chemical and Materials Engineering

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2025

Author dc:creator

• Xu, Dingmeng

Advisors dc:contributor.advisor

• Cao, Peng
• Hodgson, Michael

• Additive Manufacturing
• Titanium
• Laser Powder Bed Fusion

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/76102

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/76102