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

Monday 8:00 AM
October 10, 2022
Room: 301
Location: David L. Lawrence Convention Center

Session Chair: Alber Sadek, Edison Welding Institute; Michael Eff, Ewi


8:00 AM  
Binder Jetting of Ultra-fine 316L Austenitic Stainless Steel Powder: Microstructure Observation and Mechanical Properties: Mohammad Jamalkhani1; Mohammadreza Asherloo1; Amir Mostafaei1; 1Illinois Institute of Technology
    Ultra-fine austenitic 316L stainless steel (SS) powder was binder jetted using an advanced compaction technology equipped with an ultrasonic dispenser and double roller to enhance powder packing density. Densification was studied by vacuum sintering under subsolidus and supersolidus temperatures. It was demonstrated that supersolidus sintering facilitated densification and a final relative density of 99.4% was achieved at 1400 °C for 2 h. Microstructure analysis displayed formation of equiaxed austenitic grain with a mean size of ~33 μm in which delta-ferrite and sigma phases formed at the grain boundaries. Anisotropy shrinkage was seen with a maximum linear shrinkage of 18.4%, 17.7%, 21.5% in X-, Y-, Z-directions. Mechanical testing results showed a yield strength of 202 MPa, tensile strength of 574 MPa, elongation of 90%, and microhardness of 132 HV0.5. Fractography revealed a ductile fracture containing deep dimples in sintered parts with densities of > 99%.

8:20 AM  
Understanding Variations in Solidification Behavior of Additively Manufactured 316L Printed via Laser-Wire Directed Energy Deposition: Olivia Denonno1; Charles Smith1; Matthew Schreiber1; Kip Findley1; John Speer1; Anthony Petrella1; Craig Brice1; Jonah Klemm-Toole1; Zhenzhen Yu1; 1Colorado School of Mines
    Understanding the solidification behavior and microstructure evolution of additively manufactured austenitic stainless steels is essential for qualification of the alloy system across additive manufacturing platforms. Ferritic primary solidification that is commonly observed in conventional processes (e.g., wire-arc welding) may not necessarily occur in rapid solidification additive manufacturing processes. In this study, it was determined that solidification conditions and composition can affect the stability of austenite as the primary solidification phase relative to delta ferrite. The impacts of solidification pathway, thermal gradients and solidification velocities, and composition on solidification behavior of thin and thick laser-wire directed energy deposition 316L parts will be discussed and compared. The observed shift in solidification modes among these two builds can be modeled and understood via a comprehensive microstructure map developed using analytical solidification models. This microstructure map can be used to predict microstructure morphology and size as well as solidification mode across additive manufacturing platforms.

8:40 AM  
Understanding the Effects of Residual Stress in Mechanical Behavior of SS-316L Manufactured by Laser-wire DED Process: Sandeep Dhakal1; Allyssa Bateman1; Boyd Panton2; Jeffrey Bunn3; Brian Jaques1; 1Boise State University; 2Ohio State University; 3Oak Ridge National Laboratory
    Recent advancements in the AM technologies have shifted the focus from rapid prototyping towards high-value industrial usage. Laser-wire direct energy deposition (LW-DED) can increase the scalability of current AM processes to manufacture large scale industrial components. Since DED technology is characterized by high-energy sources which generate high temperature fields with high temperature gradients, it results in non-uniform residual stresses, causing distortion and plastic deformation of the manufactured components. Since wire-based DED process is less understood as compared to its powder counterparts, understanding the distribution of residual stress with varying process conditions and its effect on mechanical properties would provide us with insight on its structural performance for industrial usage. To do so, spatially resolved residual stress was measured across varying build geometries and interlayer temperatures, using neutron diffraction and X-ray diffraction. These values were then correlated to the microstructure and mechanical behavior of the printed components.

9:00 AM  
Influence of Substrate Geometry and Feedstock Morphology on the Mechanical and Metallurgical Properties of Direct Energy Deposition Stainless Steel 316L: Samantha Sorondo1; Jakob Hamilton1; Iris Rivero1; 1Rochester Institute of Technology
    This investigation focuses on the effect of substrate geometry and feedstock morphology on the mechanical and metallurgical properties of directed energy deposition (DED) multilayered stainless steel 316L. In remanufacturing, features to be repaired are often unchangeable; this constrains the factors that can be controlled: feedstock morphology and print parameters. Thus, understanding the interaction between feedstock morphology and substrate geometry is crucial in the decision of picking wire or powder as feedstock. For this purpose, these morphologies were compared by depositing them on substrates with varying widths and thicknesses. Statistical models to correlate microhardness, porosity, and dilution percentages were used to identify their interactions. Powder was seen to have higher dilution and microhardness for the thickest substrate while using wire showed less porosity than powder for all substrate geometries. These results are proposed in an effort to contribute to the guidelines for repairs with DED.

9:20 AM  
Effect of Surface Roughness on the Fatigue Behavior of Binder Jet Printed Ultra-fine 316L Austenitic Stainless Steel Powder: Mohammad Jamalkhani1; Amir Mostafaei1; 1Illinois Institute of Technology
    Binder jetting is an additive manufacturing method in which powder is deposited layer-by-layer and selectively joined in each layer with binder. Ultra-fine gas atomized 316L stainless steel powder is binder jetted followed by supersolidus liquid phase sintering at 1400 °C for 2 h. Micro-computed tomography observations show that though the density of the as-printed sample is ~54%, near full density of 99.4% is achieved with sintering at 1400 °C for 2 h. The objective of this research is to investigate fatigue life of as-sintered and surface treated binder jetted 316L SS samples. Surface topology analysis reveals trace number of open pores with an average surface roughness of 1.0 µm. Fatigue tests are performed under tension-compression condition at R=-1 with 20 Hz frequency. Fracture surface study is conducted on the fatigue samples to study the mechanism associated with crack initiation and propagation.

9:40 AM  
Effects of Process Parameters on Mechanical Behavior of Wire Arc Additive Manufactured (WAAM) AISI 316LSi: Vishnu Ramasamy1; John Lewandowski1; 1Case Western Reserve University
    Wire Arc Additive Manufacturing (WAAM) attracts many industries due to its high productivity, low cost, and wide range of materials. The effects of changes in process parameters on the microstructure and preliminary mechanical properties of AISI 316L(Si) produced via WAAM will be reported. Large scale deposits (≈ 10” X 2.5” X 7”) of 316LSi were manufactured in collaboration with Lincoln Electric Additive Solutions using their robotic deposition cells. The effect of changes in process parameters (P, V, travel/wire-speed/deposition rate, interpass temperature) on the microstructure, ferrite content and preliminary mechanical properties will be reported, along with the measurement of surface roughness on the as-deposited conditions.

10:00 AM Break

10:20 AM  
Effect of Hyaluronic Acid and Proteins on the Corrosion Behavior of Additively Manufactured Stainless Steel 316L: Deeparekha Narayanan1; Lin Chen1; Bilal Mansoor1; Matthew Vaughan1; Ibrahim Karaman1; Homero Castaneda1; 1Texas A&M University
    Additive manufacturing (AM) techniques such as directed energy deposition (DED) and selective laser melting (SLM) are starting to gain momentum to produce parts used in structural and biomedical applications. With the advent of newer manufacturing techniques and parameters, it has become important to study the effect of these on the corrosion resistance and development of micro-galvanic cells that could lead to localized dissolution from specific active locations. This work aims to study the corrosion and tribo-corrosion behavior of stainless steel 316L manufactured using DED and SLM in conditions simulating the inflamed joint after a total hip/knee replacement to attempt to identify unfavorable microstructural features. The individual effect of hyaluronic acid, bovine serum albumin and γ – globulin on the passive film characteristics will be studied to determine the effect of the manufacturing technique on these properties.

10:40 AM  
The Effects of Microstructure and Chemistry on Corrosion Behavior in Additively-manufactured 316L Stainless Steel: Ryan Khan1; Michael Melia1; Michael Heiden1; Sara Dickens1; Paul Kotula1; Frank DelRio1; 1Sandia National Laboratories
    Stainless steels are an important class of alloys in a variety of different structural applications. This is due in large part to their corrosion resistance, and the formation of an oxide passivation layer. In additively manufacturing (AM) stainless steels formed via powder bed fusion (PBF), processing parameters such as scan speed and laser power strongly affect the local microstructure and thereby their corrosive behavior. In this study, we employed X-ray computed tomography, white-light interferometry, electron backscatter diffraction, transmission electron microscopy, electrochemical impedance spectroscopy, and Kelvin probe force microscopy to elucidate the multiscale behavior of AM 316L stainless steel and uncover how local changes in microstructure, chemistry, and surface potential track to large scale corrosion. Moreover, five different PBF samples with varying manufacturing parameters were studied to shed light on the variability of the behavior with processing. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

11:00 AM  
Design of Decarburization after Application of Self-Terminating Dissolution to SS316L Processed by Laser Powder Bed Fusion: Soumya Sridar1; Noah Sargent1; Stephanie Prochaska2; Mitra Shabani1; Owen Hildreth2; Wei Xiong1; 1University of Pittsburgh; 2Colorado School of Mines
    Components fabricated using the laser powder bed fusion process require extensive post-processing to remove trapped powders, support structures, and surface roughness. Existing post-processing techniques, such as mechanical milling, cannot access the interior cavities. Dissolvable support technology, based on self-terminating dissolution process, has been developed for several materials to address these issues. In this work, self-terminating dissolution is applied to SS316L using sensitization at 800oC followed by etching. Using this process, the surface roughness of the as-printed part is reduced from 20 to 2 μm. This smoother surface is expected to improve mechanical performance and fluid flow. After etching, carbon accumulation was observed at the surface and decarburization heat treatment was designed using kinetic simulations performed with DICTRA. Using both simulation and experiments, the decarburization time and temperature were optimized using chemical and microstructural analysis. The mechanical properties were evaluated before and after the application of the decarburization by tensile testing.

11:20 AM  Cancelled
Corrosion Assessment of Additively Manufactured Stainless Steel 316L in Various Concentrations of Chlorides: Lin Chen1; Deeparekha Narayanan1; Bilal Mansoor2; Ibrahim Karaman1; Homero Castaneda1; 1Texas A&M University; 2Texas A&M University Qatar
    Additive manufacturing (AM) is a rapidly growing metal processing technique that not only enables the making of complex geometries but faster times to have a final product that is difficult to produce by using traditional methods. In this work, we aim to study the active-passive characteristics of stainless steel 316L manufactured using directed energy deposition (DED) and selective laser melting (SLM). Solutions with different concentrations of sodium chloride maintained at a stable pH of 8 adjusted by borate buffer were used as the electrolytes to study the effect of concentration of chlorides on the corrosion resistance of the materials. A comprehensive understanding of corrosion performance of materials was obtained by DC and AC methods. Apart from general electrochemical techniques, a microcapillary set-up will be used to target specific microstructural features to determine the most favorable features for the best corrosion resistance.

11:40 AM  
Framework for Designing Additively Manufactured Metallic Functionally Graded Materials: Allison Beese1; Zi-Kui Liu1; 1Pennsylvania State University
    By selectively depositing different powder metal feedstock at different locations within a component, directed energy deposition (DED) additive manufacturing (AM) can be used to fabricate functionally graded materials (FGMs) with spatially varying composition, and therefore, properties. However, in liquid-phase processing of mixtures of dissimilar alloys or metals, along with the far from equilibrium processing conditions accessed in AM, undesired phases (e.g., brittle intermetallics) may form, resulting in cracking during fabrication aided by thermal stresses, or resulting in failure-prone regions within the FGM. This presentation will describe our combined computational-experimental approach for understanding and predicting phase formation during AM of FGMs where the computational method of predicting phases, e.g., through equilibrium and Scheil solidification simulations, is validated or improved based on comparison with experimental findings.