2023 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2023): Materials: Metals-Mechanical Properties I
Program Organizers: Joseph Beaman, University of Texas at Austin

Monday 1:30 PM
August 14, 2023
Room: Salon F
Location: Hilton Austin

Session Chair: Joseph Beaman, University of Texas at Austin

1:30 PM
Effect of Heat Treatment on the Microstructure and Mechanical Properties of Monel K500 Alloy Fabricated via L-PBF and LP-DED: Indrajit Nandi¹; Seyed Ghiaasiaan¹; Nabeel Ahmad¹; Paul R. Gradl²; Shuai Shao¹; Nima Shamsaei¹; ¹Auburn University; ²NASA
    This study examines and compares the effects of different heat treatments on microstructure and mechanical properties of additively manufactured (AM) Monel K500 alloy fabricated using laser powder bed fusion (L-PBF) and laser direct energy deposition (LP-DED) technologies. The as-fabricated AM Monel K500 specimens displayed dendritic microstructure and elemental micro-segregation, due to high cooling rates induced during AM fabrication process, which differs significantly from its wrought counterparts. Applicability of standard heat treatments (HT) proposed in literature for wrought material was validated for the AM Monel K500 alloy using multi-step HT such as hot isostatic pressing, solution annealing, and different aging processes. The mechanical properties of test specimens were evaluated using uniaxial tensile and fatigue testing at room temperature. Microstructural evolution of the test specimens during HT was analyzed using scanning electron microscope. The mechanical properties of the L-PBF and LP-DED test specimens were discussed and compared in various heat treatment conditions.

1:50 PM
Effect of Post Thermal Processing Conditions on Physical and Mechanical Properties of LPBF Processed Inconel 718: Swathi Vunnam¹; ¹AddUp Inc
    Laser powder bed fusion (LPBF) processed material performance strongly depends on the post thermal processing conditions. This study investigates the material properties of Inconel 718 processed through a roller recoating process with fine powder having a median particle size D50 <11 痠 in different post-thermal conditions. Three sets of specimens were printed using identical printing conditions and tested in as-built, stress-relieved, and solution-aged post thermal conditions. Average material density ≥ 99.95% and surface roughness Ra < 4 痠 was achieved across the build platform in as-built condition. Homogenization coupled with double aging achieved superior mechanical properties with a significant increase in hardness and tensile strength. This study demonstrates that the combination of the roller spreading mechanism with fine powder can be utilized to produce high-quality parts by employing the appropriate post thermal processing.

2:10 PM
A Comparison of Microstructure and Mechanical Performance of Inconel 718 Manufactured via L-PBF, LP-DED, and WAAM Technologies: Nabeel Ahmad¹; Alireza Bidar¹; Reza Ghiaasiaan¹; Paul Gradl²; Shuai Shao¹; Nima Shamsaei¹; ¹Auburn University; ²National Aeronautics and Space Administration
    The microstructure and mechanical properties of additively manufactured (AM) alloys can be significantly affected by variations in cooling rates, resulting from different process conditions across different additive manufacturing (AM) platforms. Therefore, it is crucial to understand the effect of manufacturing process on the microstructure and mechanical properties of AM Inconel 718. This study examines three AM processes: laser powder bed fusion, laser powder directed energy deposition, and wire arc additive manufacturing. Results show that fully heat treated laser powder bed fused (L-PBF) and wire arc additively manufactured (WAAM) Inconel 718 specimens exhibit higher strength compared to laser powder directed energy deposited (LP-DED) ones due to finer grain structure in L-PBF and retained dendritic microstructure in WAAM. The ductility in LP-DED Inconel 718 was slightly higher compared to WAAM and L-PBF due to relatively small carbide size, which causes stress concentration in a small material volume, leading to delayed fracture.

2:30 PM
Microstructure and Mechanical Properties of Additively Manufactured Haynes 282: A Comparative Analysis between L-PBF and LP-DED Technologies: Nabeel Ahmad¹; Reza Ghiaasiaan¹; Paul Gradl²; Shuai Shao¹; Nima Shamsaei¹; ¹Auburn University; ²National Aeronautics and Space Administration
    This study compares the microstructure and tensile properties of Haynes 282 fabricated using laser powder bed fusion and laser powder directed energy deposition. Both sets underwent stress-relieving, followed by hot isostatic pressing, and the standard double aging heat treatment. Tensile testing was conducted at room temperature on specimens fabricated with both technologies to evaluate and compare their tensile behaviors. Results show that the ultimate tensile and yield strengths of laser powder bed fused specimens were 18% and 57% higher, respectively than those of laser powder directed energy deposited ones, whereas the elongation to failure was similar in both. The difference in strengths is attributed to the differences in the size of γ' precipitates and grains, i.e., those in the LP-DED specimens being larger, whereas similar elongation to failure is attributed to the carbide debonding dominating the fracture mechanism in both batches.

2:50 PM
Mechanical Performance of LPBF Manufactured Haynes 282: Nicholas Lamprinakos¹; Junwon Seo¹; Anthony Rollett¹; ¹Carnegie Mellon University
    Haynes 282 is a nickel-based superalloy which excels in high temperature structural applications. While it has traditionally been used as a wrought product, its relatively high weldability makes it a good candidate for laser powder bed fusion (LPBF). But parts produced via LBPF often have significantly different microstructures, and thereby properties, compared to wrought parts. Furthermore, as a precipitation strengthened alloy, Haynes 282 generally requires heat treatment, which needs to be optimized for the printed material. In this study, Haynes 282 samples were printed with different printing parameters and orientations and were subject to varying post-printing heat treatments. The microstructures of the samples were observed before and after heat treatment to characterize grain structure, crystallographic texture, and precipitate structure. Hardness, tensile, and creep testing was performed to evaluate the effect of the processing conditions on the mechanical properties and to compare the properties to literature values for wrought Haynes 282.

3:10 PM Break

3:40 PM
Effect of Heat Treatments on the Tensile Properties of Additively Manufactured 15-5 PH Stainless Steel: Rukesh Gusain¹; Paul Gradl²; Shuai Shao¹; Nima Shamsaei¹; ¹Auburn University; ²NASA Marshall Space Flight Center
    This study investigates the effect of post-manufacture heat treatments on the mechanical properties of 15-5 PH stainless steel (SS) fabricated by laser powder-directed energy deposition (LP-DED). Two different heat treatment procedures (CA-H900 and CA-H1150) were performed, and their influence on the microstructure was examined using the scanning electron microscope. Tensile tests were performed to evaluate the mechanical properties at cryogenic and room temperatures. The elongation at failure was significantly higher for specimens treated with CA-H1150 than those with CA-H900 at both testing temperatures. In contrast, the ultimate tensile and yield strengths of CA-H900 specimens were higher than CA-H1150 specimens. The fractography examinations reveal that the specimens treated with CA-H900 exhibited brittle behavior at cryogenic temperature.

4:00 PM
Johnson-Cook Failure Model for Additively Manufactured 304L Stainless Steel Parts: Henry Haffner¹; Manoj Kumar Reddy Rangapuram¹; Siva Sai Krishna Dasari¹; Sriram Praneeth Isanaka¹; K. Chandrashekhara¹; Mario F. Buchely¹; Joseph W. Newkirk¹; ¹Missouri University of Science and Technology
    Laser powder bed fusion (LPBF) process is a type of additive manufacturing technique which uses a powder bed to form complex metal parts in a layer-by-layer process. This study aims to understand the damage initiation in the parts manufactured by LPBF process using 304L stainless steel powder, which is widely used in numerous applications. The tensile specimens were manufactured using 304LSS powder through LPBF. Tensile specimens with varying notches were tested to calibrate the parameters of the constitutive Johnson-Cook failure model. To obtain the strength parameters, the tensile tests were performed at different temperatures and strain-rates. The material model developed was used in numerical simulation of the tensile tests and compared with the experimental results.

4:20 PM
Influence of steel alloy composition on the process robustness of as-built hardness in laser-directed energy deposition: Jonathan Kelley¹; Joseph Newkirk¹; Laura Bartlett¹; Todd Sparks²; Sriram Praneeth Isanaka¹; Saeid Alipour¹; Frank Liou¹; ¹Missouri University of Science and Technology; ²Product Innovation and Engineering, LLC
    To ensure consistent quality of additively manufactured parts, it is advantageous to identify alloys which can meet performance criteria while being robust to process variations. Toward such an end, this work studied the effect of steel alloy composition on the process robustness of as-built hardness in laser-directed energy deposition (L-DED). In-situ blending of ultra-high-strength low-alloy steel (UHSLA) and pure iron powders produced 10 alloys containing 10-100% UHSLA by mass. Thin-wall samples were deposited, and the hardness sensitivity of each alloy was evaluated with respect to laser power and interlayer delay time. The sensitivity peaked at 40-50% UHSLA, corresponding to phase fluctuations between lath martensite and upper bainite depending on the cooling rate. Lower (10-20%) or higher (70-100%) alloy contents transformed primarily to ferrite or martensite, respectively, with auto-tempering of martensite at lower cooling rates. By avoiding martensite/bainite fluctuations, the robustness was improved.

4:40 PM
The Variation of Mechanical Properties of M300 Maraging Steel Manufactured with Varying Process Parameters in Laser Powder Bed Fusion: Haley Petersen¹; Bradley Sampson¹; David Failla¹; Matthew Priddy¹; Zackery McCleland²; ¹Mississippi State University; ²US Army Engineer Research and Development Center
    Laser powder bed fusion (L-PBF) is a type of additive manufacturing (AM) that uses layers of powdered metal and a laser to manufacture a part in a layer-by-layer fashion. L-PBF has the ability to use a variety of process parameters for production of fully dense parts with satisfactory mechanical properties. Maraging 300 steel (M300) is a material of interest due to its combined tensile strength and high strength-to-weight ratio. This study aims to determine optimal process parameters of M300 manufactured using L-PBF by comparing the parameters effects on the resulting mechanical properties. Specifically, the primary process parameters (e.g., laser power and scan speed) were varied based on literature review and the as-built properties (e.g., tensile strength, and hardness) and conditions (e.g., surface roughness and porosity) were explored through statistical means for determining an acceptable parameter range.