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Materials Science in Additive Manufacturing In-situ alloying of Ti41Nb by LPBF
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the geometrical constraints inherent in traditional graded implants that enhances osseointegration. However,
manufacturing methods, including subtractive and challenges persist in achieving optimal compositions
formative techniques. Among the various metal AM and eliminating porosity and compositional segregation,
methods, 2-12 laser powder bed fusion (LPBF) stands out as particularly due to the significantly different melting
one of the most widely adopted approaches, 7,8,13,14 capable of points of refractory β stabilizers like Nb, Ta, Mo, and
producing strong metallic components while maintaining Ta compared to Ti. Efforts to address these challenges,
a lower entry cost, ease of use, and simplified maintenance such as laser re-melting, 7,29,32 have shown promise but
compared to electron beam powder bed fusion. In the struggle to strike a balance between reducing unmelted
LPBF process, a powder layer is first spread, followed by particles and preventing keyhole porosity. A recent study
laser melting of a predetermined area to build up a slice by Huang et al. has demonstrated innovative approaches
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of a part, after which the previously solidified layer moves to mitigating these challenges. By employing beam
down, where the powder spreading and melting process is shaping techniques, such as using a top-hat beam profile
repeated. Moreover, achieving a multi-material component and a short stripe width scanning strategy, along with high
enhances the performance of LPBF parts by integrating power high-speed scanning, large and stable melt pools
various desired properties into a single piece. In this with low aspect ratios can be achieved. Short stripe width
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regard, it is crucial to consider the complex “fish scale” strategy is a scanning strategy that makes out of short
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interface to optimize interfacial performance. 16,17 LPBF scanning vectors (in the scale of 1 mm), to which there
is known for creating heterogeneous structures, which is little time for the scanned region to cool down before
provide opportunities to implement extrinsic toughening the adjacent scan comes in, hence leading to very short
mechanisms as well as simultaneously enhance material “thermal rest time” that aids in melt pool manipulation
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strength and ductility. LPBF has found a particularly from a typical single track melt pool to a larger melt pool.
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strong foothold in the manufacturing of titanium and This method has shown to significantly reduce porosity
its alloys (not titanium aluminide), with a diverse range and improve homogeneity, while also increasing printing
of α- to β-based Ti alloys, 18,20 particularly applications speed compared to traditional Gaussian laser approaches.
in aerospace and biomedical industries, where weight In addition, the role of unmelted β-titanium stabilizers,
reduction and/or bespoke design is important. such as Nb and Ta, presents intriguing insights. Alternating
In the realm of biomedical implant engineering, the bands of regions with unmelted Nb and homogeneous
development of titanium alloys with β stabilizers through areas have been shown to enhance extrinsic toughening
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LPBF has gained significant attention. These implants play a of TiNb, improving crack propagation behavior. A study
crucial role in restoring or augmenting biological structures, by Brodie et al. suggests that keyhole porosity may play a
enhancing quality of life, and even extending lifespan. more critical role than unmelted Ta in nucleating fatigue
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However, traditional implant materials like SS316L, CoCr, cracks. Furthermore, samples with more unmelted Ta
and Ti6Al4V, derived from other industries, often lack have demonstrated greater ductility compared to those
ideal properties for implantation, leading to issues such as with more homogenized distributions. 33
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implant loosening and cytotoxicity. Moreover, these alloys Inspired by the innovative approach of Huang et al.,
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have high elastic modulus that leads to “stress shielding” which utilized a short stripe width scanning strategy to
effect, which based on the Wolff’s law, the bone in a healthy encourage interaction between individual melt pools, this
person will adapt to the loads in which it is placed—bone study aims to further explore the impact of thermal rest
resorption can occur when stress is shielded. To address time variation on a single part. By employing a contour
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these challenges, researchers are turning to new materials scan from the part’s center outward, different thermal
like β-titanium alloys, which incorporate non-toxic rest times can be achieved at various locations within
elements like Nb, Ta, Zr, Mo, and Sn to achieve lower elastic the component. This approach offers an opportunity to
modulus, greater strength, and corrosion resistance. 23-25 In investigate how varying thermal rest times influence the
addition, innovative manufacturing methods, particularly microstructure and mechanical properties of the part,
LPBF, offer the ability to create complex structures and providing more insights into future attempts to achieve
tailor properties for enhanced performance. in situ alloying.
LPBF of biomedical β-titanium alloys is often Utilized in this study was 41 wt.% Nb—the approximate
conducted through in situ alloying, 7,8,7-31 offering weight required to achieve a fully stabilized β phase
compositional flexibility, cost-saving benefits, and shorter in Ti-Nb system, which is essential for reducing the
lead times. This approach allows for the adjustment of alloy Young’s modulus of titanium alloys and minimizing the
compositions and potentially the creation of functionally stress shielding effect of bioimplants (where the implant

Volume 3 Issue 3 (2024) 2 doi: 10.36922/msam.3506