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Materials Science in Additive Manufacturing AM-produced CoCrFeMnNi properties

Figure 5. X-ray diffraction analysis results of selective laser melting-produced CoCrFeMnNi at 450 and 750 mm/s scanning speeds before and after heat
treatment.

densification of SLM-produced CoCrFeMnNi. It is clear A B
that a scanning speed between 700 and 800 mm/s can
lead to very low porosity, and thus the scanning speed of
750 mm/s was chosen to produce samples for mechanical
property evaluation. Meanwhile, a scanning speed between
400 and 500 mm/s exhibit acceptable porosity, and thus the
scanning speed of 450 mm/s was chosen for comparison
purpose. Additional relative density measurements show
that the relative density values for 450 mm/s and 750 mm/s
are 93.8% and 97.4%, respectively.
C D
3.2. Microstructure analysis
Figure 5 shows the results of XRD analysis for the SLM-
produced CoCrFeMnNi using the two scanning speeds
of 450 and 750 mm/s before and after heat treatment.
FCC single phase was detected in all the four conditions.
The XRD results obtained in this study are typical for
CoCrFeMnNi produced by laser AM processes, such as
SLM [13,14] and laser DED [50,51] . No significant shift in peak
locations was observed among the studied materials,
indicating that the chosen range of scan speed as well as Figure 6. SEM micrographs of selective laser melting-produced
CoCrFeMnNi (450 and 750 mm/s scanning speeds, before and after heat
heat treatment had negligible effect on crystal structure treatment) in the DD-TD cross section. (A) 450 AB; (B) 450 HT; (C) 750
and phase composition of the studied materials. AB; and (D) 750 HT.
Figure 6 shows SEM images of the DD-TD section of
CoCrFeMnNi samples before and after heat treatment. The homogenization effect, and thus the melt pool boundaries
450 AB sample consists of layer-wise microstructure, but are no longer clearly revealed. However, a similar pattern
the melt pool marks are not regularly stacked due to the can be observed in terms of elongated grains. The average
frequent change of SD. The microstructures of samples grain width of 450 HT sample is approximately 85 μm, while
before and after heat treatment are very similar, while that of 750 HT sample is between 50 and 80 μm. Although
there is a small difference in average size of melt pools. SEM observations found no such particles, some powder
The average melt pool length of 450 AB condition is about did not fully melt in the SLM process. This is evident from
140 μm, while that 750 AB condition is approximately the fact that unmelted particles are present on the fracture
120 μm. The smaller size of melt pools of 750 AB sample surface of Charpy samples (Figure 16E). However, they are
can be explained by the lower energy density applied in the not randomly scattered across the fracture surface but only
SLM process. Consequently, less material is melted at the found inside few isolated colonies and therefore should not
faster scanning speed sample. Heat treatment provides the be present in abundant amount in the obtained materials.

Volume 2 Issue 1 (2023) 7 https://doi.org/10.36922/msam.42