Page 67 - MSAM-3-3

Materials Science in Additive Manufacturing In-situ alloying of Ti41Nb by LPBF
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Table 3. EDS material composition results for samples 60‑1 Table 4. Summary of mean layer HV value across samples
to 60‑4 60‑1 to 60‑4
Sample 60‑1 Mean layer HV value
A B C Sample 60‑1 Sample 60‑2 Sample 60‑3 Sample 60‑4
Weight % Top layer 268±27 267±72 313±23 340±28
Titanium 0.13 76.07 57.58 Layer 2 276±34 294±64 324±29 336±31
Niobium 96.81 17.18 38.54 Layer 3 269±18 309±62 320±27 315±24
Others 3.06 6.75 3.88 Layer 4 264±25 317±50 336±38 319±41
Sample 60‑2 Base layer 283±26 338±63 341±40 316±35
A B C D Mean 272±26 306±62 327±31 325±32
Weight %
Titanium 81.96 0.00 63.98 100.00
Niobium 18.04 100.00 36.02 0.00
Others 0.00 0.00 0.00 0.00
Sample 60‑3
A B C D
Weight % Figure 11. Schematic of Vickers microhardness indentation profile (Y-Z
Titanium 79.88 96.85 62.12 0.00 plane)
Niobium 20.12 3.15 20.51 96.50
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Others 0.00 0.00 17.37 3.50 β phase. This is consistent with previous work on Ti-Ta,
Sample 60‑4 where increasing tantalum to stabilize the β phase first
A B C D increases the strength followed by decreasing it.
Weight % Samples 60-1, 60-2, and 60-3 have base layer HV values
Titanium 87.84 77.71 3.15 66.86 that are higher than the other layers within the sample.
This observation could be explained by the downward heat
Niobium 12.16 22.29 89.20 33.14 dissipation during the melting process as the base layer
Others 0.00 0.00 7.65 0.00 conducts heat from layers above to the LPBF base plate
Abbreviation: EDS: Energy dispersive spectroscopy. beneath. The heat accumulation and the continued exposure
to thermal energy (through conduction) raised its hardness
mean Vickers hardness (HV) value for each layer (row) was value, likely due to the precipitation of isothermal nano-sized
computed and is presented in Table 4 for all four samples. ω phase, which was known to precipitate at a temperature
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iso
as low as ~250°C. This observation suggests that the
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On initial inspection of the microhardness results,
sample 60-2 exhibits a significantly higher standard composition of the base layer of most samples in this study is
not sufficiently β-stabilized to suppress ω phase formation.
deviation (Table 4) for its mean layer microhardness, iso
which is consistent with the high % porosities within 3.6. Tensile properties of LPBF-produced samples
the sample. Hence, there are chances that point on the Samples 60-2 and 60-4 were chosen for replication in tensile
surface “collapse” instead of being indented. Furthermore, testing due to their contrasting sample quality. Processing
sample 60-2 also contains a high number of unmelted Nb parameters, except for the scanning strategy, used for
particles. The difference in hardness between pure Nb and sample 60-2 (scanning speed of 481 mm/s) were applied
Ti-Nb alloy can result in the high standard deviation for to fabricate tensile samples 481-1 (1 mm stripe width) and
hardness.
481-10 (10 mm stripe width), utilizing a stripe scanning
There is a trend of increasing HV value from sample strategy, to assess their tensile performance. Similarly, the
60-1 and it peaked at 60-3 (Figure 12). This trend suggests processing parameters for sample 60-4 (scanning speed
that material hardness has a limited positive correlation of 317 mm/s) were employed to fabricate tensile samples
with the amount of Nb alloying (due to increased melting 317-1 and 317-10. As evidenced by the results from the
and homogenization of Nb particles), which leads to solid contour scan, identical laser parameters but differing
solution strengthening. Beyond the peak value, the reduction thermal rest times can result in significant differences in
of HV values could be attributed to the stabilization of the porosity and the amount of unmelted Nb.

Volume 3 Issue 3 (2024) 10 doi: 10.36922/msam.3506