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Materials Science in Additive Manufacturing AM-produced CoCrFeMnNi properties

SLM system was to be obtained. For this purpose, laser equipped with a 3-electrode system, which consists of HEA
power (P), hatch spacing (H), and layer thickness (T) sample working electrode, a Ti wire as a counter electrode,
were fixed at 100W, 60 μm, and 20 μm, respectively, and Ag/AgCl reference electrode. Area of 10 × 10 mm
while the laser scanning speed (V) was varied from 200 was exposed to the electrolyte. To ensure a steady-state
to 800 mm/s. While this study intends to obtain various potential, an open circuit potential (OCP) was measured
energy density input by adjusting the scanning speed for 1 h. Potentiodynamic polarization curves were
alone, it is well recognized that other parameters may have performed at a scan rate of 5 mV/s. Five measurements
significant effect on the obtained properties [40,41] . Note that were performed for each condition to ensure the accuracy
the coding of sample conditions combines the numerical of the results, which was evaluated by calculating the
value of SLM laser scanning speed and the status of heat standard error of these measurements.
treatment. For instance, 450 AB indicates the condition of
450 mm/s. The resultant volume energy density, defined 2.2. Material characterization
3
as P/(V•H•T), ranged 104.2 – 416.7 J/mm . As a result, Cubic specimens obtained in the first stage of SLM
seven small cubes of 5 × 5.6 × 5 mm were obtained, as experiment were analyzed by measuring their density and
shown in Figure 1. Based on the porosity observation by visually analyzing their polished side whose normal
and relative density measurement, the appropriate laser is perpendicular to DD. Density of these cubes were
scanning speeds were determined for the next stage. In the measured with Archimedes method according to ASTM
second stage, with the same settings on laser power, hatch B962 and compared to the bulk density of 8.05 g/cm for
3
[42]
spacing, and layer thickness, two laser scanning speeds CoCrFeMnNi . Furthermore, the optical micrographs of
[36]
were selected for building larger specimens for mechanical polished cubic specimens were processed by the software
property evaluation. Tensile test pieces were produced as a ImageJ, and thus the porosity of obtained materials was
scale-down version of the subsize rectangular tensile test obtained. For the specimens obtained in the second stage
specimen according to ASTM E8/E8M. Their length is of SLM experiments, they were cutoff the build plate after
56.4 mm. The length of the specimens was oriented along SLM using wire EDM. For the Charpy test, V-notch was
scan direction (SD), width along the deposit direction cut by wire EDM on the surface parallel to DD for the
(DD), and thickness along transverse direction (TD), as Charpy block specimens. The impact tests were performed
shown in Figure 2. Charpy specimens were prepared in using a JBS-300B Charpy Impact Testing Machine. Since
accordance with the ASTM E23 standard, as shown in the absorbed impact energy of CoCrFeMnNi does not
Figure 3. Each block for Charpy test is 55 mm in length, significantly change within a broad temperature range ,
[22]
10 mm in width, and 10 mm in height. Charpy test in the current study was performed only at
To investigate the effects of heat treatment (annealing) room temperature. Besides the measurement of absorbed
on the microstructures and mechanical properties, half impact energy, the lateral expansion on the compression
[43]
of the fabricated Charpy samples and half of the tensile side of the specimens was also evaluated . For the tensile
samples were heat treated in a vacuum tube furnace specimens, tensile tests were performed on a Shimadzu
(Model: KJ-T1700-60IC). This heat treatment strategy, Autograph AGS-X 50 kN machine at a crosshead speed
adopted from other studies [26,29] , consisted of ramping at of 1 mm/min at room temperature. Furthermore,
the rate of 10°C/min up to 1000 °C/min, dwell time of 2 h, Vickers microhardness was obtained on the cross-section
and then quenching in water. (as defined in Figure 2A) of as-built (AB) and heat-treated
(HT) samples. The applied load was 0.1 kg with dwell time
Electrochemical corrosion experiments were conducted of 15 s. Nine indentations were made in the matrix array
in 3 M NaCl solution at room temperature. Corrosion with indentations being 0.5 mm apart from each other.
samples were ground to 1200 grit sandpaper and then
polished with 1 μm diamond slurry. Electrochemical studies Metallographic samples were cut, ground, polished
were performed with a potentiostat (WaveDriver 100) and then etched with a solution consisting of C H OH
5
2
(25 mL) + HCl (25 mL) + CuSO H O (5 g). A scanning
4.5
2
electron microscope (model: FEI SCIOS) with electron
backscatter diffraction (EBSD) capability was adopted for
microstructure and texture analysis. For obtaining reliable
results, three EDS area scans at different heights along DD
were obtained and the averages were taken. Meanwhile, for
phase identification, X-ray diffraction (XRD) profiles were
Figure 1. Selective laser melting-produced CoCrFeMnNi test cubes for obtained for the materials obtained in the second stage of
scanning speed selection. SLM experiment, using a X’Pert Pro X-ray diffractometer

Volume 2 Issue 1 (2023) 4 https://doi.org/10.36922/msam.42