2024 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2024): Materials: Metals I
Program Organizers: Joseph Beaman, University of Texas at Austin

Monday 1:30 PM
August 12, 2024
Room: 602
Location: Hilton Austin

Session Chair: John Obielodan, University of Wisconsin-Platteville; Arnoldas Sasnauskas, Trinity College Dublin

1:30 PM
Compressive Strength of 3D Printed 17-4 PH Honeycomb Structure: Haijun Gong¹; Juan Sierra¹; Reece Woodard¹; Yue Zhang¹; Lianjun Wu¹; Shaowen Xu¹; ¹Georgia Southern University
    Engineered honeycomb structures are commonly used to reduce part weight and material usage. However, the traditional manufacturing processes for honeycomb structures are inflexible and only limited to simple shapes. With 3D printing, the honeycomb structure can be effectively manufactured and integrated into complex part designs. This study adopted the newly introduced metal-polymer filament of 17-4 PH stainless steel and conducted fundamental research about the compressive strength and engineering-absorption capability of 17-4 PH honeycomb structures fabricated sequentially by material extrusion based 3D printing, debinding, and sintering. Compression testing was performed to evaluate the in-plane compressive strength of the honeycomb structure. The stress-strain curve was acquired to identify the plastic collapse and densification onset, to further understand its energy-absorption capability. Metallographic characterization and porosity measurement were also conducted to discuss the failure mode under the compression loading scenario.

1:50 PM
Evolution of Porosity in Additively Manufactured Steel 316L Dog Bone Specimens Under Tension: X-Ray Computed Tomography Study: Fidel Baez¹; David Moore²; Borys Drach¹; ¹New Mexico State University; ²Sandia National Laboratories
     An ex-situ study of porosity evolution under tension was performed on laser powder bed fusion manufactured stainless steel 316L dog bone specimens with a 2.4x2.4 mm cross-section and 10.4 mm long test section using X-ray computed tomography (CT). Five specimens were scanned before loading was applied and after each of the three tensile loading steps: (1) 20% strain, (2) maximum stress, and (3) failure. CT data were analyzed to compute the volume and maximum linear dimensions of individual pores, as well as to obtain spatial distributions of these quantities within the specimens. Additionally, the fracture surfaces were analyzed using a scanning electron microscope (SEM). Initiation locations of cracks that led to ultimate failure were identified in the initial scans. The results showed that cracks leading to failure grew as a result of the coalescence of small pores in closely spaced clusters.

2:10 PM
Effect of Heat Treatment on the Micro-/Defect-structure and Mechanical Behavior of Additively Manufactured Alf357 Aluminum Alloy: Md Faysal Khan¹; Paul Gradl²; Donald Godfrey³; Jacky Diemann⁴; Shuai Shao¹; Nima Shamsaei¹; ¹Auburn University; ²NASA Marshall Space Flight Center; ³SLM Solutions NA, Inc.; ⁴SLM Solutions Group AG
    This study investigated the effect of heat treatment (HT) on the micro-/defect-structure and room temperature tensile and fatigue behaviors of AlF357 fabricated using laser powder bed fusion. Two different HT sequences, consisting of stress relieving (SR), hot isostatic pressing (HIP), and T6 (i.e., SR+HIP+T6 and SR+T6+HIP), were examined. For SR+T6+HIP, all defects still present after T6 were eliminated after the final HIP. For SR+HIP+T6 a few defects closed after HIP had reopened. The grain structure remained comparable for both HTs. SR+HIP+T6 exhibited approximately 45% and 32% higher yield and ultimate tensile strength, respectively, due to increased Mg2Si precipitate population and size compared to SR+T6+HIP. However, the presence of large and populous η-Fe (Al8Mg3FeSi6) precipitates lowered ductility by around 6% for SR+HIP+T6 compared to SR+T6+HIP. Specimens in SR+HIP+T6 showed higher fatigue resistance for the alloy than those in SR+T6+HIP.

2:30 PM
Effect of Heat Treatment on the Micro-/Defect-structure and Tensile Behavior of Additively Manufactured A6061-RAM2 Aluminum Alloy: Md Faysal Khan¹; Reza Ghiaasiaan¹; Paul R. Gradl²; Shuai Shao¹; Nima Shamsaei¹; ¹Auburn University; ²NASA Marshall Space Flight Center
    This study investigated the effect of heat treatment (HT) on micro-/defect-structure and room temperature tensile behavior of A6061-RAM2 alloy fabricated using laser powder bed fusion. Specimens were fabricated via reactive additive manufacturing strategy, using a mixture of Ti and B4C inoculant particles into pre-alloyed A6061 powder. These particles acted as grain boundary pinners and facilitated the formation of equiaxed grains. Effect of different post-process HTs, including hot isostatic pressing (HIP), solutionizing (SOL), and aging (AGE), conducted at varying temperatures and durations were examined. All HTs incorporating HIP greatly reduced defect content compared to non-heat-treated condition but had minimal impact on the grain structure of the alloy. It showed noticeable changes in tensile strengths and ductility with variations in SOL (at 500-530 °C for 1.5-2 hrs) and AGE (at 160-180 °C for 8-34 hrs) temperature and duration. Tensile strengths increased, while ductility decreased with higher SOL temperature and longer AGE durations.

2:50 PM
Phase-field Simulations of Solute Element Segregations at Various Interfaces in Additively Manufactured IN718 Ni-based Superalloy: Masayuki Okugawa¹; Katsuhiko Sawaizumi¹; Yuichiro Koizumi¹; Takayoshi Nakano¹; ¹Osaka University
    Solute segregation significantly affects material properties and is a critical issue in the laser powder bed fusion (L-PBF) additive manufacturing (AM) of Ni-based superalloys. Therefore, understanding solute segregation is essential for fabricating reliable parts avoiding cracks. In the L-PBFed parts, there are various interfaces, such as interdendritic boundaries, melt pool boundaries, and impinging interfaces at the central part of the melt pool. Segregation behavior and crack susceptibilities are suggested to differ in these interface regions. In the present study, we investigated the solute element segregation behavior at the various interfaces under rapid cooling conditions by the multiphase-field method. We found that significant solute segregations occur at the interfaces, and the solute segregation behavior of solute elements largely depends on the regions of the melt pool. Moreover, the sensitivities of the various interfaces to liquation and solidification cracks also differ, reflecting the solute segregation behavior.

3:10 PM Break

3:40 PM
Hydrogen Embrittlement Relaxation of Stainless Steel via Powder Metallurgy Manufacturing Technology: Jihoon Jeong¹; Seung-Wook Baek²; Jung Hyun Kim³; ¹Texas A&M University; ²Korea Research Institute of Standards and Science; ³Hanbat National University
    Hydrogen is considered a sustainable energy carrier for the future, but it impacts negatively on the mechanical characteristics of metal materials, called hydrogen embrittlement. A new mechanism to ensure hydrogen embrittlement resistance in austenitic stainless steel metal parts is studied for hydrogen service based on powder metallurgy manufacturing technology. An advanced method for ensuring high hydrogen embrittlement resistance is developed by controlling nitrogen content in the gas atomization and powder metallurgy manufacturing processes so that martensite phase transformation is suppressed and a stabilized austenite phase is maintained. Through precise in-situ mechanical testing in a gaseous hydrogen environment, it is observed that the deformation and work hardening are substantially alleviated. Additionally, a nitrogen-controlled SS304L material produced using powder metallurgy-based manufacturing technology exhibits “caramel-like high-strength superplastic deformation” that significantly reduces the necking phenomenon occurring during general metal deformation by avoiding local stress concentration and inducing stress relaxation.

4:00 PM
The Impact of Different HIP Treatment Cycles on Fatigue Behavior during 4-Point Bending of Additively Manufactured (AM) Ti-6Al-4V: Diego Ariza¹; Edel Arrieta¹; Cristian Banuelos¹; Chad Beamer²; Ryan Wicker¹; Francisco Medina¹; ¹The University of Texas at El Paso; ²Quintus Technologies
    The fatigue behavior of Additive Manufacturing (AM) Ti-6Al-4V has been widely investigated under axial loading, with limited analysis of its performance under bending conditions. Internal defects in AM parts can detrimentally affect the integrity of 3D-printed specimens, impacting their fatigue performance. Researchers have previously implemented the Hot Isostatic Pressure (HIP) post-processing method to address the presence of defects. This study explores the fatigue life of L-PBF Ti-6Al-4V after three HIP treatments: standard, low temperature/high pressure (LTHP), and super beta HIP, alongside annealed heat treatment. Optical techniques were utilized to assess microstructure, while tensile and hardness testing examined mechanical properties. Fracture morphologies and stress-life (S-N) curves were analyzed to understand fatigue behavior. Initial findings indicate that specific HIP post-processing can enhance the fatigue performance of Ti-6Al-4V under 4-point bending.

4:20 PM
Exploring Convergent Manufacturing Pathways For 316L Hot Isostatically Pressed Parts: Kameswara Pavan Kumar Ajjarapu¹; Fred List III¹; Jason Mayeur¹; Sam Bell¹; Chase Joslin¹; Brian Jordan¹; Sebastien Dryepondt¹; Soumya Nag¹; Ryan Dehoff¹; ¹Oak Ridge National Laboratory
    Metal additive manufacturing (AM) evolved over the last decade to serve the current manufacturing needs. However, the tradeoff between cost, lead time, part complexity, size, and scalability for parts produced via AM versus powder metallurgy (PM) is still a point of contention. This talk demonstrates the feasibility of a combined AM + PM approach to fabricate metal parts which benefit from the intrinsic advantages of both AM and PM. Powders of 316L stainless steel (SS) were poured into canisters fabricated via (1) conventional extrusion, (2) laser powder bed fusion (LPBF), and (3) blown powder directed energy deposition (BP-DED) and then degassed and subjected to HIPing. Post-HIP specimens were characterized for microstructure, physical, and mechanical properties. This study provides a preliminary overview of the opportunities and challenges associated with the AM + PM approach and offers valuable insights that can further guide the fabrication of complex, large-scale metal components.

4:40 PM
Variations Across Length Scales in Additively Manufactured Ti- 6Al-4V Parts: Challenges to Repeatability and Reproducibility: Venkatavardhan Sunderarajan¹; Utkarsh Thakre¹; Suman Das¹; ¹Georgia Institute of Technology
    Repeatability and reproducibility of parts produced in Laser Powder Bed Fusion (LPBF) Metal Additive Manufacturing (AM) remains a major challenge despite significant research on the process' capabilities. This study focuses on the variations in microstructural, dimensional and static mechanical properties of Ti-6Al-4V parts produced by LPBF Metal AM. The property variations within different regions of a part, from part-to-part, build-to-build and machine-to-machine will be presented. In addition to part geometry, the location, orientation as well as layer thickness have varying impacts on the measured part properties. Vast amounts of heterogeneous data from multiple sensors capture process information in real-time across length and time scales. The correlations of in-situ process signatures with post-build property measurements will also be presented. Finally, the challenges of (and limits to) successfully manufacturing multiple parts with critical geometries repeatably across the build plate will be explored.