Page 52 - MSAM-4-1

Materials Science in Additive Manufacturing Additive manufacturing of 316L-Cu alloys

50%, 70%, 90%, and 100%). After dehydration, the outer surface of an implant first upon entering the body,
samples were treated with hexamethyldisilane (HMDS) the surface properties play a critical role in determining
overnight. A gold coating layer was applied to the samples the overall antibacterial efficacy.
to facilitate the imaging of organic material through SEM. XRD measurements were performed on all three
A minimum of n = 3 images were collected per time point compositions to identify the phases present, as shown in
and composition for bacterial colony quantification. Figure 3 listed in Table 1. The XRD pattern of 316L exhibited
The antibacterial efficacy of each material composition a primary characteristic peak at a 2θ value of 43.64°,
was determined by counting the number of bacterial corresponding to face-centered cubic (FCC) austenite in the
colonies (N) on the surface of the samples using an open- (111) plane. Notably, the SS-3Cu and SS-5Cu compositions
source object counting software (DotDotGoose, USA). showed an increased intensity of the (111) peak relative to 316L,
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Antibacterial efficacy (R), based on the control and which can be attributed to adding Cu. However, the intensities
treatment CFU counts at each time point, was calculated of the secondary peaks [(200), (220), and (311)] remained
as follows: essentially unchanged. This selective enhancement of the

(111) peak suggests that Cu addition induces a preferential
N − N
×
R = control treatment 100 (I) orientation of the grains. In addition, SS-3Cu peaks exhibited
N control a slight shift in the negative direction (~0.15°), which further
increased in SS-5Cu (~0.22°). No martensitic phases were
3. Results detected in the XRD patterns of 316L, and no new peaks were
detected in SS-3Cu and SS-5Cu within the detection limit,
3.1. Microstructure, EDS, and phase analysis suggesting that Cu addition did not lead to the formation of
The microstructure of 316L consisted of distinct any new phases compared to the 316L scan pattern.
regions exhibiting both cellular and columnar dendritic 3.2. Compression and hardness testing
solidification modes. The regions appeared to have a
uniform structure, with clear boundaries between the two The compressive behavior of all three compositions was
formations. Figure 1A displays a low-magnification image found to be similar, as illustrated by the representative
of 316L, showing four printed layers, with a mix of cellular stress-strain curves shown in Figure 4A. The yield stress
and columnar structures across the layers. The transition values for 316L, SS-3Cu, and SS-5Cu were 334 ± 9 MPa,
between these two formations is distinctly visible at higher 329 ± 12 MPa, and 317 ± 1 MPa, respectively. Cu addition
magnification. The columnar dendrites are oriented along appeared to have minimal impact on the yield stress. This
the heat flow direction, or normal to the top and bottom is advantageous for implant applications, where 316L
surface of each layer, and largely aligned in the vertical is commonly used, as adding Cu would not result in a
direction due to cooling provided by the substrate. Figure 1B substantial change in strength. Figure 4B presents the
and C also reveal a similar mix of cellular and columnar Vickers hardness measurements taken along the build
dendrite structures, with no significant differences between direction, starting from the bottom of the sample. The
these compositions and the 316L base material. Equiaxed hardness values of 316L, SS-3Cu, and SS-5Cu were 209 ±
structures for 316L, SS-3Cu, and SS-5Cu were measured 12, 183 ± 9, and 186 ± 10 HV 0.2, respectively. Although
with diameters of 5 ± 1 μm, showing that Cu addition did both Cu compositions exhibited lower hardness than 316L,
not change grain size significantly. All three compositions no significant difference was observed between SS-3Cu
resulted in fully dense samples, except for minor gas and SS-5Cu. Moreover, hardness measurements for all
entrapment defects. These defects, caused by trapped gas three compositions showed no significant variation across
particles during the solidification of the melt pool, appeared
as spherical voids of 30 μm or less. Table 1. XRD angle and peak intensity values of 316L,
EDS was conducted to examine the Cu distribution SS‑3Cu, and SS‑5Cu
within the 316L base composition. As seen in Figure 2, Peak hkl 316L (2θ, SS‑3Cu (2θ, SS‑5Cu (2θ,
Cu was uniformly distributed within 316L, suggesting the no. Intensity a.u.) intensity a.u.) intensity a.u.)
formation of a solid solution. Chromium and nickel, the 1 (111) 43.64°, 313 43.49°, 455 43.42°, 429
main alloying elements of 316L, also appeared evenly 2 (200) 50.69°, 146 50.51°, 149 50.47°, 161
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distributed. Achieving a uniform Cu distribution is ideal
for implant applications where a consistent antibacterial 3 (220) 74.52°, 52 74.38°, 52 74.35°, 49
effect is desired across the surface of an implant. Since 4 (311) 90.41°, 61 90.27°, 66 90.13°, 67
bacteria and other foreign materials typically contact the Abbreviation: hkl: Miller indices denoting crystallographic plane
orientation.

Volume 4 Issue 1 (2025) 4 doi: 10.36922/msam.7357