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Materials Science in Additive Manufacturing Inconel 718-CoCrMo bimetallic structures

Figure 2. (Left) Inconel 718 – CoCrMo bimetallic structure. (Right) SEM/EDS analysis of the bimetallic interface. Note that the interface is not visible in
the SEM micrograph, but the compositional variations mark the interface in the EDS mapping.

with the bimetallic interface appearing smaller than
the substrate interface. The illuminated circles are tiny
gas pores, which are more frequent and extensive in the
Inconel 718 region than in the CoCrMo region. For the
SEM image, a seemingly blank photo is observed with no
qualitative distinction between the two materials and the
interface. However, the EDS mapping indicates a relatively
smooth transition between the elements, meaning there
is little to no elemental segregation. No cracking or other
defects are observed at the interface, which confirms that
these materials are compatible .
[28]
3.2. Hardness
Figure 3. Vicker’s hardness profile of Inconel 718-CoCrMo bimetallic
Vicker’s hardness tests were conducted on polished samples structure.
and the results are shown in Figure 3. The tests show that the
base hardnesses in the Inconel 718 and CoCrMo zones were displays up to 0.4 strain for that sample. The failure behavior
about 260 HV and 430 HV, respectively. A hardness profile of the two bimetallic structures is illustrated in Figure 5.
was established, measuring at every 50 μm distance within
the interface zone until the pure alloys were reached. The 3.4. Oxidation studies of bimetallic samples
profile shows a linear variation within the interface region. For the oxidation and followed by hardness measurements,
The linear profile confirms no brittle intermetallic phase samples were tested at 800°C for 96 h. No significant
formations and reveals that the interface is about 150 µm variations in hardness were observed. Only a slight
wide. decrease in hardness (430 HV to 400 HV) was observed

3.3. Compression testing in the CoCrMo part, which occurred as a byproduct of
the oxidation test since recrystallization would also occur.
Figure 4 shows stress-strain curves for the four types of non- Figure 6 shows the SEM/EDS analysis of the oxide layer
heat treated compression samples. The test’s primary purpose formed in each constituent. For Inconel 718, a strongly
was to understand the role of the interface in compressive adherent chromium oxide layer was formed along with
deformation behavior. It was found that the interface some pits. This pitting resulted from the depletion of Cr
properties did not limit the compressive deformation in near the interface, which made the material under the oxide
bimetallic structures but were instead controlled by the bulk layer prone to the effects of oxidation. For the CoCrMo side,
materials. The transverse bimetallic samples had the worst spalling was observed, meaning that the oxide layer was not
yield strength, with the base CoCrMo sample performing the strongly attached to the base material. Furthermore, a Cr
best. The Inconel 718 samples did not fail, so the plot only depletion zone was not observed in the CoCrMo part.

Volume 1 Issue 3 (2022) 4 https://doi.org/10.18063/msam.v1i3.18