Laser Powder Bed Fusion Additive Manufacturing of Fe-based Shape Memory Alloys for Biomedical Applications

Biodegradable Fe-Mn-Si alloys are promising candidates for biomedical implant applications, combining degradability with desirable mechanical performance and shape memory properties. However, the inherently slow corrosion rate of iron-based alloys poses challenges that limit their practical clinical application. This thesis addresses these issues by employing laser powder bed fusion (LPBF) additive manufacturing (AM) to fabricate Fe-30Mn-6Si biodegradable alloys with tailored degradation behaviours and mechanical properties. Specifically, this thesis systematically investigates the effects of LPBF process parameters—including laser power, scanning speed on microstructural evolution, phase constitution, corrosion behaviour, and fatigue performance. The relationship between process-induced microstructure and accelerated degradation rates in simulated physiological conditions is carefully explored by evaluating the formation and characteristics of corrosion products. The in-situ alloying of mixed elemental powder creates a heterogeneous multi-phase composition (γ-austenite, ε-martensite, α-Fe and tiny αFeSi) that establishes micro-galvanic reactions. The rapid solidification during LPBF produces an ultra-fine grain structure, dramatically increasing grain-boundary density and providing preferential pathways for localised attack. The unique cellular structure also helps improve the corrosion rate due to the Mn/Si segregation along the boundary. Furthermore, compression-compression fatigue performance under physiological loading conditions is comprehensively assessed, investigating the critical interaction between cyclic mechanical loading and corrosion phenomena in porous Fe-Mn-Si scaffolds fabricated by mixed metallic powder and pre-alloyed powder. Findings highlight the substantial influence of different powder preparation methods (mixed versus pre-alloyed) on the corrosion kinetics, fatigue performance, and lifespan of the biodegradable implants. LPBF‐fabricated Fe–Mn–Si scaffolds tuned by powder type show that pre‐alloyed powders produce dense, uniform microstructures with high strength and fatigue resistance ideal for long‐term, load‐bearing implants, whereas mixed powders yield fine, multiphase porous structures with accelerated, stable corrosion suited to temporary or low‐load applications. Under cyclic loading, corrosion and fatigue synergistically accelerate damage, yet both scaffold types retain structural integrity up to ~60 % strain, enabling a customizable balance between mechanical durability and resorption rate for orthopaedic implants. Overall, this work advances the scientific understanding of LPBF materials processing in tuning advanced biodegradable alloys, facilitating the future clinical translation of customised, safe, mechanically stable FeMnSi-scaffolds for orthopaedic applications.

Grantor dc:publisher

UNSW, Sydney

Year dc:date

2025

Author dc:creator

• Chen, Wenliang

Statement dc:rights

• embargoed access
• CC BY 4.0

Licence

• http://purl.org/coar/access_right/c_f1cf
• https://creativecommons.org/licenses/by/4.0/

Language dc:language

en

Identifier

https://doi.org/10.26190/unsworks/31402

OAI identifier oai:identifier

oai:unsworks.library.unsw.edu.au:1959.4/105493