Additive Manufacturing: Materials, Alloy Development, Microstructure and Properties: Additive Manufacturing of 316L
Program Organizers: Prashanth Konda Gokuldoss, Tallinn University of Technology; Zhi Wang, South China University of Technology; Jurgen Eckert, Erich Schmid Institute of Materials Science; Filippo Berto, Norwegian University of Science and Technology

Tuesday 2:00 PM
November 3, 2020
Room: Virtual Meeting Room 3
Location: MS&T Virtual

Session Chair: Somayeh Pasebani, Oregon State University

2:00 PM
Microstructure Analysis of Laser Additive Manufactured 316L Stainless Steel: Sudhakar Vadiraja¹; Penn Rawn¹; ¹Montana Technological University
    The objective of this research is to investigate the microstructures of 316L stainless steel produced by laser additive manufacturing (LAM), as a function of build angle orientations and global energy densities. Microstructures were characterized using a Leica DM750P optical microscope, paired with Leica application suite software. Microstructure studies revealed that the grain size was only marginally affected by the build angle orientation. Higher energy density samples showed relatively coarser cellular structure with highly aligned dendritic morphology. At relatively lower energy densities, several large faceted voids were observed with unfused powder particles within the voids. Micro-voids were minimal and almost no unmelted particles were noticed at relatively higher GED values, due to more complete melting conditions. A combination of fine and coarse cellular structures was observed for 30° build angle orientation samples as opposed to only very fine cellular or dendritic structures for the 0° orientation samples.

2:20 PM
Grain Orientation Analysis of Additively Manufactured 316L Stainless Steel: Ann Choi¹; Anthony Rollett¹; ¹Carnegie Mellon University
     Process variables in additively manufactured 3D metal print designs are known to affect their microstructural evolution, texture and defect structures. In particular, variations in power and velocity are known to affect melt pool geometry in 316 stainless steel parts built with laser powder bed fusion. Consequently, it is expected that these parameters will also directly affect how the solidifying grains grow into the fusion zone. Results obtained from electron backscatter diffraction will be used to visualize and quantify grain growth direction and grain orientation gradients as a function of different laser process parameters. Honeywell Federal Manufacturing & Technologies is operated for the United States Departmentof Energy under Contract Number DE-NA-0002839

2:40 PM
Microstructure and Corrosion Characteristics of 316L Stainless Steel Fabricated by Laser Powder Bed Fusion Process: Balachander Gnanasekaran¹; Yao Fu¹; ¹University of Cincinnati
    In this study, microstructural and corrosion characteristics of AM 316L SSs have been investigated using advanced microscopic characterization techniques and electrochemical testing. The variation of critical microscopic features with printing parameters are identified. Correspondingly, the changes observed in the corrosion resistance in 3.5% NaCl indicated by the pitting corrosion resistance and their relationship with microstructure and printing conditions are identified. It is found that the AM 316L SSs, in general, demonstrate an improved corrosion resistance compared with conventionally manufactured 316L, reflected by increased pitting potential. Both hatch spacings show an increase in pitting potential with laser power followed by a decrease. Solidification texture affects the corrosion resistance as shown by the difference in pitting potential tested on the two perpendicular surfaces. The enhanced pitting corrosion resistance of AM 316L compared with the conventional ones is likely to relate to the dislocation cells and solidification texture of the AM sample.

3:00 PM
Failure Evolution and Mechanisms in Additively Manufactured Stainless Steel 316L Under Dynamic Loading Conditions: Katie Koube¹; Kaila Bertsch²; Greg Kennedy¹; Dan Thoma²; Josh Kacher¹; Naresh Thadhani¹; ¹Georgia Institute of Technology; ²University of Wisconsin - Madison
    Here we describe the spall evolution and failure mechanisms in 3D printed Stainless Steel 316L (SS316L) fabricated through Powder Bed Fusion (PBF). Spall failure is driven by the interaction between defect structures and grain orientations relative to shock wave propagation. Thus, the spall properties and failure responses of PBF SS316L vary based on the process parameters and resulting microstructures. PBF manufactured cylinders were impacted using an 80-mm gas gun at a range of pressures in order to generate varying levels of failure. The target fixture employs two samples, one instrumented to capture free surface velocity profiles and one soft recovered for postmortem microstructure characterization. EBSD in combination with SEM and TEM is used to determine the role of microstructure on spall initiation and propagation. Effects of heterogeneous microstructural defects including voids, melt pool lines, and texture preferences, as contributing to initiation of dynamic tensile and spall failure will be discussed.

3:20 PM
Understanding The Influence of Porosity and Microstructure On Mechanical Behavior in Additive Manufactured 316L Stainless Steel Using In-situ X-ray Computed Tomography and Electron Microscopy: Aeriel Murphy-Leonard¹; David Rowenhorst¹; Richard Fonda¹; ¹Naval Research Laboratory
     Three-dimensional techniques such as x-ray micro-computed tomography (XCT) enable the ability to fully visualize and quantify porosity and provide fundamental relationships between pore size and morphology on mechanical behavior and damage evolution. In the current study, the influence of pore and void size, morphology, and distribution on crack initiation, growth, and coalescence during tensile and cyclic loading was examined using a lab based XCT system and in-situ synchrotron XCT. The material examined wasadditively manufactured (AM) 316L stainless steel. The specimens were produced using laser powder bed fusion techniques where the gauge diameter was 1 mm. Static XCT revealed that in conditions where the cross-sectional area is small majority of the porosity was in-homogeneously distributed where a higher distribution of porosity was found near the surface which is commonly seen in additively manufactured materials. It was also determined that cracks initiated at near surface defects in the specimen during fatigue.