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Materials Science in Additive Manufacturing Y O influence in heat-treated LPBF IN718 composite
2 3

phase dissolves during the heat treatment, the amount of Due to the sample being furnace-cooled at the end of the
Nb available in the matrix increases. This provides extra solutionizing treatment, this provides extra time for the δ
material for the formation ofδ phase, which has a chemical phase to form.
formula of Ni Nb. Second, according to the TTT diagram Further analysis of sample 1075-Y shows that multiple
3
of IN718, the δ phase starts to form at approximately nano-sized precipitates can be observed near or embedded
980°C, which is below the solutionizing temperature.
inside the Laves phase particles as shown in Figure 10A.
Extensive analysis by line scan EDX shows that the
A B
compositions of the precipitates are a combination of Nb,
Ti, Y, N, and O elements. The precipitates that are embedded
in the Laves phase particles have 1 common trait, which is
the presence of Ti and N in all of them, as shown in Region
2 in Figure 10B and Region 1 in Figure 10D. On the other
hand, Y may or may not be detected in those precipitates as
C D shown in the presence of Y peak in Region 1 in Figure 10D
but not in Region 2 in Figure 10B. However, it can also
be seen that O can be detected in both cases of embedded
precipitates, suggesting that Y could also be present but
only in a minute amount. Most of the time, the precipitates
that exist outside of the Laves phase have both Y and Ti as
well as O, while N is not detected. This can be observed in
Figure 7. Optical micrographs of etched samples 1075-0 (A), 1075A-0 Region 1 in Figure 10B and Region 2 in Figure 10D. Due to
(B), 1075-Y (C), and 1075A-Y (D). The black dashed lines indicate the
grain boundaries. the lack of element N, these precipitates that are observed
in sample 1075-Y are the Y-Ti-O complex precipitates that
A B were reported in other literature [32,33] .
However, the precipitate formation that is similar to the
observed precipitates in sample AP-Y can still be found
in sample 1075-Y as shown in Region 3 in Figure 10D. In
addition, large Y O particles and large TiN particles can
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2
be detected next to each other as shown in Regions 1 and
C D 2 in Figure 10C. As such, all these observations further
support the conclusion made previously in which Y O
2
3
nanoparticles have a high tendency to combine with other
elements in the IN718 to form complex precipitates.
After the IN718/Y O composite has been solutionized,
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2
two additional observations can be made. First, the
Figure 8. Scanning electron microscopy images showing the presence of embedded precipitates within the Laves
microstructures of samples 1075-0 (A), 1075A-0 (B), 1075-Y (C), and phase suggests that reprecipitation of Laves phase during
1075A-Y (D). The yellow dashed lines indicate the grain boundaries. cooling has occurred and trapped other precipitates within

A B

Figure 9. Scanning electron microscopy images showing the microstructures of samples 1075-0 (A) and 1075-Y (B).

Volume 1 Issue 4 (2022) 7 https://doi.org/10.18063/msam.v1i4.25