Page 60 - MSAM-3-3

Materials Science in Additive Manufacturing In-situ alloying of Ti41Nb by LPBF

absorbs most of the load, thereby reducing stress on the 2.2. Fabrication of tiles with contour scanning
surrounding bone, which can lead to surrounding bone strategy
resorption and implant loosening). To contextualize the Tabulated in Table 1 are the process parameters and
alloy composition selected for this study, achieving a resulting volumetric energy density for each of the
low Young’s modulus coupled with adequate strength is sample tiles. The processing parameters were selected
crucial, typically achieved by retaining the full β-phase based on the maximum energy density of 410 J/mm³ used
with minimal alloying additions. It is widely recognized in a study on TiNb by Huang et al., which served as the
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that two minima in Young’s modulus are observable, upper limit. The laser power and powder layer thickness
primarily at approximately 42 wt.% Nb, where the material were maintained at 390 W and 0.05 mm, respectively.
consists predominantly of the β-phase and is attained The hatch spacing was reduced from the leftmost column
through quenching. Extending this understanding to to the right. To maintain the energy density across each
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LPBF, Wang et al. investigated in situ alloying of Ti-xNb row, the laser scanning speed for each sample tile was
alloys (where x = 0, 15, 25, 45 at.%) using LPBF. Their calculated accordingly. The samples produced in this step
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findings highlighted that the composition with 25 at.% would be used for microstructural and microhardness
Nb (approximately 39 wt%) exhibited the lowest Young’s analysis. To study the effect of thermal rest time, the anti-
modulus compared to other compositions, owing to clockwise contour scanning pattern and LPBF-fabricated
its ability to retain the β-phase with minimal niobium tile samples were used, as shown in Figure 1A and 1B,
content. Furthermore, despite the presence of unmelted Nb respectively. The sample tiles were all produced with the
particles, the in situ alloyed Ti40.5Nb (wt.%) demonstrated same laser scanning strategy, anti-clockwise contour
a notably low average Young’s modulus of 77 GPa. 36 scan, but with varied hatch spacing between the laser

2. Materials and methods Table 1. LPBF processing parameter for Ti‑Nb tile samples
2.1. Printing of Ti41Nb specimens Dimension 15 mm×15 mm×5 mm
The samples prepared in this study were fabricated using LPBF (height)
through in situ alloying. The CP-Ti powder used (Grade 2 Laser power 390 W
ASTM B348; LPW Technology Ltd, UK) has an average Layer thickness 0.05 mm
particle size of 43.5 μm, whereas the Nb powder (Tecnisco Hatch spacing (mm)
Advance Material Pte Ltd, Singapore) shows particle sizes 0.08 0.06 0.04 0.02
distributed between 20 and 63 μm. The powder was first Scanning 1 488.00 650.00 975.00 1950.00 1 Energy density
sieved using an automated vibrating sieving machine with speed (199.80) (200.00) (200.00) (200.00) (J/mm )
3
a 63 μm metal screen to prevent the potential clog-up of the (mm/s)
powder supply system and the creation of printing defects. 2 361.00 481.00 722.00 1444.00 2
After that, the powder mixture was weighed, where 41 wt.% (270.08) (270.27) (270.08) (270.08)
of Nb was identified as the required alloying component as it 3 287.00 382.00 574.00 1147.00 3
theoretically results in a Mo equivalence of 11.48%, which is (339.72) (340.31) (339.72) (340.02)
close to the 10% Mo equivalent required for a fully stabilized 4 238.00 317.00 476.00 951.00 4
β phase as presented above. Hence, for the batch of powder (409.66) (410.09) (409.66) (410.09)
prepared for the LPBF process, it consists of 41 wt.% Nb and Note: The energy density associated with each laser scanning parameter
59 wt.% CP-Ti. is given in parenthesis.
The sieved and weighed mixture of CP-Ti
Grade 2 (59 wt.%) and Nb powder (41 wt.%) was held A B
in the metallic cylindrical container supplied with 2.5 kg
of CP-Ti powder and fitted onto the Inversina 2L 2-axis
powder mixer (Bioengineering AG, Switzerland). It
is continuously mixed for 12 h at 60 rpm to achieve a
homogeneous mixture of Ti-41Nb. To ensure the powder
mixture does not segregate over time to the largest extent
during the LPBF process, the powder mixture is prepared
directly before the scheduled LPBF printing. The SLM 280
HL machine by SLM Solutions GmbH (Germany) was Figure 1. (A) Anti-clockwise contour scan for tile samples. (B) As-built
used for this study. Ti-Nb samples on CP-Ti base plate

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