Page 31 - MSAM-1-4

Materials Science in Additive Manufacturing Process optimization of SEBM IN718 via ML

magnification present the similar microstructure of slender The reason for the formation of shrinkage porosity was
columnar grains from SEBM-fabricated Inconel 718 with that insufficient liquid reached the channel that was
processing parameters, as shown in Table 4. The columnar isolated by dendrite bridging during solidification . Three
[50]
grains were parallel to the BD, which was also observed in precipitates can be observed in the matrix of these samples,
other works about SEBM process [25,45,48] . as shown in Figure 9B, and Figure 9C is the corresponding

Further, characterization shows that the main defect in EDS map. According to the morphology and element
the sample with even surface morphology was the voids enrichment, the block shape precipitate “a” is enriched in
[17]
parallel to the BD, as shown in Figure 9A. This defect was Nb and Mo, which is determined as Laves phase . The
also observed in samples with uneven and porous surface long plate shape precipitate “b” is the δ phase. Laves phase
morphology. The voids were distributed at the inter- is mainly formed on the grain boundaries and mixed with
dendritic region with a width of 2–3 μm and a length of 20 a few of δ phase somewhere. The polygonal precipitate “c”
μm. These voids are considered the shrinkage porosity . is enriched in N and Ti, indicating the existence of TiN
[49]
phase. The spherical precipitate “d” in the core of TiN is
A B rich in Al and O, which suggests that the precipitate is the
Al O phase. No gas pore defects were observed inside the
2
3
sample.
The difference between grains was observed by EBSD.
Figure 10 shows the EBSD-IPF maps on the cross-section
parallel to the BD. Strong texture in the as-built samples
C D along the BD was observed in the EBSD-IPF maps. The
as-EBM-built samples mainly consist of columnar grains
with preferential orientation <001>, decorated with few
equiaxed fine grains. Figure 11 shows the pole figures
and multiple of uniform density (MUD) maximum of
four samples. Sample P2 shows a strong texture in BD
with a MUD maximum of 30.73, sample P1 and P3 shows
Figure 8. BSE images at low magnification showing the similar slender a reduced texture, and sample P4 has the lowest MUD
columnar grains in different samples: (A) P1, (B) P2, (C) P3, (D) P4. maximum, which is 17.21. Completely equiaxed grain

A C

B

Figure 9. BSE images of defects and phase in selective electron beam melting -fabricated Inconel 718: (A) shrinkage porosity, (B) Laves phase, δ phase, and
TiN/Al2O3 phase, (C) EDS map of the inclusion in (B).

Volume 1 Issue 4 (2022) 8 https://doi.org/10.18063/msam.v1i4.23