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Materials Science in Additive Manufacturing AM-produced CoCrFeMnNi properties

A B

Figure 2. Selective laser melting (SLM)-produced CoCrFeMnNi tensile samples. (A) Selected tensile samples attached to the build plate after SLM;
(B) dimensions of tensile samples.

A B

Figure 3. Charpy test of selective laser melting-produced CoCrFeMnNi. (A) Schematic orientation of Charpy specimen during the test (ASTM E23); (B) a
Charpy specimen before and after test.

equipped with Cu target. The scan was performed in the usually cause lack of fusion (LOF) defects as laser fails to
2θ range of 35° to 100° and with tube voltage and current provide sufficient energy to generate full melting of powder
of 40 kV and 44 mA, respectively. The fracture surfaces layers, which leads to the formation of pockets of unmelted
of Charpy V-notched samples were also characterized powder particles or even delamination from the previously
[44]
by surface appearance as seen in the scanning electron deposited layers . The second region of energy density
microscopy (SEM) images. domain is the target for process parameter optimization
and can be characterized by the reduced porosity fraction.
3. Results and discussion In the third region, excessive overheating caused by high
energy density generates surface temperatures that exceed
3.1. Effect of scanning speed on relative density and the evaporation point of an alloy causing particles and
porosity molten material to eject from heat-affected zone, resulting
[45]
The criterion for selecting the proper scanning speed was in large spherical pores . Strong vaporization and spatter
based on the porosity or the density of the SLM-produced lead to shortage of molten metal to fill the molten track.
[46]
materials. Figure 4A shows the optical micrographs of As a result, a printed part is left with many voids .
the cross sections of cubic samples obtained under the Moreover, high energy density may cause vaporization of
seven scanning speeds. It is clear that the density and size low melting elements, which becomes entrapped and leads
of pores increase as the scanning speed decreases. This to the formation of pores. Inert gas dissolved in the molten
phenomenon can be explained by the following. It is well metal and released during solidification as well as moisture
known that incorrect choices of laser energy density in SLM present on the surface of powder particles may also be the
[45]
often result in formation of defects. Depending on defect source of gaseous porosity .
types, the energy density domain for SLM can be split In the present study, energy density optimization was
into three regions. Low energy densities in the first region performed by varying the scanning speed, and the scope

Volume 2 Issue 1 (2023) 5 https://doi.org/10.36922/msam.42