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Materials Science in Additive Manufacturing Customized scans and dwell time on AM 316L

Two-dimensional X-ray diffraction (2D-XRD) analysis 3. Results
was conducted using a Bruker D8 DISCOVER instrument
(BRUKER, USA) equipped with a Vantec 500 General 3.1. Relative density and surface roughness
Area Diffraction Detector (GADDS) (BRUKER, USA). 23,24 As shown in Table 2, an average density >99% was
The samples were scanned using a Cu Kα radiation source obtained with slight improvement in bidirectional printed
with a wavelength (λ) of 1.54 Å, with an electrical voltage samples (i.e., S4, S5, and S6) compared to unidirectional
of 50 kV and a current of 1000 mA. A beam size of 0.5 mm printed samples (i.e., S1, S2, and S3). Table 2 also includes
was used for all scans. For the acquisition of rocking curve the average surface roughness (S ) of the printed samples.
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scans, a total of four sequential GADDS frames (detector The average S value was relatively lower for unidirectional
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positions) were captured, each frame having an exposure scans compared to bidirectional samples, possibly due to
time of 240 s. Furthermore, {111} pole figure scans the consistency of the toolpath in unidirectional printing
were performed, with the detector positioned at {111} and the absence of abrupt direction changes. 15
orientation, while the sample was rotated about the surface 3.2. Microstructure analysis
normal (φ-scan) over a full 360° range in 1° increments,
with each exposure lasting 10 s. To investigate the variation Figure 4 displays SEM images of two samples:
of crystallographic orientation along the build direction, unidirectional S1 (Figure 4A and B) and bidirectional S4
each sample was scanned at two different positions, namely (Figure 4C and D). The microstructure harbors several sub-
the top and bottom along the build direction. cellular structures comprising both elongated cell structures
and equiaxed substructures, along with a minor presence
Micro-indentation testing was conducted on the epoxy- of pores. These variations arise from differing thermal
mounted finished samples utilizing the Micro Combi histories and rapid solidification during laser melting.
Tester: MCT indentation system. During this testing, a The dashed line-circumscribed areas in Figure 4A and C
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maximum loading force of 5 N was applied, with a loading are magnified in Figure 4B and D, respectively; locations
and unloading rate set at 1000 mN/min. In addition, there of EDS measurements are indicated. EDS spot analysis at
was a 10-s dwell time at the maximum load point during different locations showed a slight variation in elemental
each indentation. To ensure the reliability of the measured composition, as evident in Table 3. Compared to the
results, an average of five indentations were performed at cellular substructure (spots 2 and 5), domain boundaries
three different locations: top, middle, and bottom sections (spots 1 and 4) exhibit a notable decrease in Fe content
along the build direction. The reduced elastic modulus and a corresponding increase in Cr, Mo, and Si levels. EDS
(E*) was determined using the Oliver–Pharr method. 25,26 spots 3 and 6 are dark regions within the microstructure.
Tensile testing was performed using Instron 5969 at room A comparative study on microstructure analysis of all
temperature at 10 s nominal strain rate using ASTM printed samples showed a similar sub-cellular structure
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E8 standard. The cylindrical test specimens were printed with minor chemical segregation.
vertically along the build direction. Before tensile testing,
the gauge length of the tensile specimens was assessed 3.3. Two-dimensional X-ray diffraction analysis
for the internal defects analysis using a Skyscan 2214 Figure 5A shows the four-frame rocking curve-stitched
Bruker micro-CT system coupled with 0.5 mm Cu filter 2D-XRD patterns of S1 (Figure 5A-i) and S4 (Figure 5A-ii)
at 1.75 μm pixel resolution under 140 kV source voltage samples, and Figure 5B depicts the 2θ integration plot
and 52 μA current. To assess the layer-wise porosity and of all printed samples. The 316L SS phase is distributed
visualize any internal defects, a 3D model of the scanned randomly, as evidenced by the arbitrary distribution of χ
samples was generated. 27,28 This involved masking the bulk angles of the diffraction peaks at the specified 2θ locations.
metallic material and the air volume within the samples, A singular austenitic face-centered cubic (FCC) phase is
ultimately allowing for the determination of the volume observed with no detection of foreign phase peaks. The
fraction of pores within the specimens. crystallographic planes {111}, {200}, {220}, and {311} were

Table 2. Relative density and surface roughness of as‑printed samples
Parameters Samples
S1 S2 S3 S4 S5 S6
RD (%) 99.72±0.18 99.15±0.12 99.13±0.14 99.94±0.13 99.92±0.19 99.86±0.16
S (μm) 15.45±0.68 14.37±0.11 14.85±0.18 19.77±0.12 18.22±0.21 17.10±0.19
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Abbreviations: RD: Relative density; S : Surface roughness
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Volume 3 Issue 1 (2024) 4 https://doi.org/10.36922/msam.2676