Session: 03-03-01: Annual Congress-Wide Symposium on Additive Manufacturing I

Paper Number: 166166

Effect of Laser Scanning Speed and Power on the Underlying Meso-, and Microstructure of Ss316l Manufactured Using Laser Powder Bed Fusion 

The ability to produce reliable and reproducible components using additive manufacturing (AM) is crucial to serve the need for customization, on-demand manufacturing, and reduced lead times across various industries. Laser powder bed fusion (LPBF) is a promising method for rapid-prototyping and consolidating parts, particularly for complex structures with high precision. To replace conventional manufacturing, LPBF should exhibit reliable and repeatable mechanical properties. LPBF offers a host of advantages, including unparalleled design flexibility, reduced post-processing requirements, and minimal material wastage. Austenitic stainless steel (SS316L) is one of the most widely used materials in LPBF due to its excellent processability and applicability in the aerospace, marine, energy, and biomedical industries.  

In this research, we meticulously evaluate the meso-, macro-, and microstructural characteristics of additively manufactured (AM) SS316L using optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The investigation focuses on the porosity formation, meltpool geometry, and grain morphology under predetermined process parameters. A constant hatch spacing of 50 µm and variable scanning speed (143–829 mm/s) and laser power (50–290 W), to maintain a constant volumetric energy density (VED) of 100 Jmm^-3 was used to manufacture cylindrical-shaped specimens. OM images of the internal cross-section surface revealed porosities such as sintering (an extreme case of lack of fusion), lack of fusion (LoF), and balling defects.  

Upon electrochemical etching of the surface, the geometrical and dimensional variation of the meltpool was observed throughout the specimens. The meltpool geometry at the sintering and LoF exhibited a smaller meltpool size compared to the layer thickness attributed to insufficient heat to penetrate the powder layer. Meanwhile, the balling phenomenon led to an unprecedented "wavy" meltpool pattern, attributed to excessive heat input and subsequent swelling. After the meltpool analysis, the EBSD data such as grain orientation, inverse pole figure (IPF), and microstructural characteristics such as grain size and average aspect ratio were analyzed to understand the behavior under various process parameters. Even though the meltpool characteristics varied, these variation led to the porosity formation, while the underlying grain morphology remained same in all specimens at constant VED. The orientation maps and IPF indicated that the grains were irregular and elongated columnar rather than equiaxed, with grain orientation in the build direction.  

The lack of understanding of the microstructural characteristics at constant VED with variable process parameters is an area that is less investigated by the research community. The goal of this research is to elucidate the microstructural characteristics of SS316L specimens under varying process parameters while maintaining a constant VED of 100 Jmm^-3. By conducting a comprehensive investigation into the effects of laser scan speed and power variations on surface and microstructural features such as surface morphology, grain size, grain orientation, grain morphology and molten pool behavior, the study seeks to provide valuable insights for optimizing LPBF process parameters to achieve the desired microstructural properties in SS316L components.

Presenting Author: Saneej Samad UTAH STATE UNIVERSITY

Presenting Author Biography: PhD candidate in Mechanical Engineering from Utah State University. Currently, working in projects primarily focusing on understanding the process-structure-property relationship of AM single alloy (SS316L) and Multi-material additive manufacturing.

Authors:

Saneej Samad UTAH STATE UNIVERSITY
Tasrif Ul Anwar utah state university
Patrick Merighe Utah State University
Nadia Kouraytem Utah State Univeristy