Page 67 - MSAM-3-1

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

A C

B D

Figure 9. Scanning electron microscopy micrographs of tensile fractography section of S1 (unidirectional) sample (A and B) and S4 (bidirectional) sample
(C and D). Magnification: (A and C): ×21; (B and D): ×3500.

Table 5. Tensile test results of printed samples 4.2. Effect of dwell time between layers on print
properties
Samples Yield strength Ultimate tensile Elongation
(MPa) strength (MPa) (%) The LENS-based DED AM process facilitates controlling
S1 360 583 38.21 the inter-layer print duration “dwell time” that can aid in
S2 379 579 30.39 controlling thermal gradient and inter-layer cooling rate.
S3 367 562 32.00 Longer dwell time between successive print layers
S4 325 583 50.27 results in a higher cooling rate and a low-temperature
S5 295 521 38.56 gradient, which contribute to the production of a finer
S6 320 501 33.26 microstructure with relatively lower S , as evidenced
a
by the numerical depiction of surface roughness of a
whereas bidirectional printing results in a more uniform series of specimens given in Table 2. Despite achieving
microstructure. The consistent toolpath in unidirectional a finer microstructure, the tradeoff is that the increase
printing, without abrupt changes in direction, in dwell time and increased porosity, i.e., lack-of-
17
likely contributes to slightly lower surface roughness fusion (Table 4), likely yielded inferior mechanical
(S ) compared to bidirectional printed samples, as properties shown in Table 5. In contrast to the findings
a
21
characterized in Table 2. Unidirectional printed specimens by Denlinger et al., we did not observe any major
also show lower porosity, owing to better control over the distortion on printed specimens upon increasing the
layering process and enhanced fusion between successive interlayer dwell time.
layers. This reduction in porosity in unidirectional prints
minimizes the risk of voids or porosity in the deposition 5. Conclusion
direction. The role of customized scan pattern and interlayer dwell
The lower porosity in unidirectional printed specimens time on the microstructure and properties of 316L
has a notable influence on the mechanical properties, SS fabricated using a LENS-based DED process was
resulting in slightly improved tensile properties and investigated in this study. The resulting product after
hardness, as outlined in Table 4. These findings underscore the DED process was a heterogeneous microstructure
the importance of customized scan patterns in tailoring consisting of both columnar and equiaxed cellular
microstructural features and properties of parts fabricated substructure with minor inter-grain chemical segregation.
by metal AM. Two-dimensional XRD results confirmed the presence of a

Volume 3 Issue 1 (2024) 8 https://doi.org/10.36922/msam.2676