Additive Manufacturing: Solid-State Phase Transformations and Microstructural Evolution: Steels
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Additive Manufacturing Committee, TMS: High Temperature Alloys Committee, TMS: Phase Transformations Committee
Program Organizers: Bij-Na Kim; Andrew Wessman, University of Arizona; Chantal Sudbrack, National Energy Technology Laboratory; Eric Lass, University of Tennessee-Knoxville; Katerina Christofidou, University of Sheffield; Peeyush Nandwana, Oak Ridge National Laboratory; Rajarshi Banerjee, University of North Texas; Whitney Poling, General Motors Corporation; Yousub Lee, Oak Ridge National Laboratory
Wednesday 8:30 AM
March 17, 2021
Room: RM 5
Location: TMS2021 Virtual
Session Chair: Eric Lass, The University of Tennessee Knoxville; Peeyush Nandwana, Oak Ridge National Laboratory
8:30 AM
The Crystallography and Orientation of Cellular Features in Additively Manufactured 316L: Richard Fonda1; Joseph Aroh2; Jerry Feng1; David Rowenhorst1; 1Naval Research Laboratory; 2Carnegie Mellon University
Laser powder bed fusion of 316L stainless steel produces a fine cellular substructure within the grains. Although these cellular structures have often been associated with enhancements in the as-built properties, their origins and characteristics are not well understood. They exhibit a variety of morphologies and orientations on polished 2D surfaces, with aspect ratios ranging from equiaxed to very elongated. In addition, the cells can exhibit multiple orientations even within the same grain. We will present a systematic characterization of the two- and three-dimensional crystallography and orientation of these cellular features, and will discuss how the observed characteristics relate to the local crystallography, local crystal growth direction, thermal gradient, and overall build direction.
8:50 AM
The Dislocation and Composition Microstructure Evolution and Mechanical Properties of Selective Laser Melted Stainless Steels: Markus Sudmanns1; Yejun Gu1; Jaafar El-Awady1; 1Johns Hopkins University
One major challenge in Additive Manufacturing (AM) of metallic components is developing an understanding of the relationship between the microstructural evolution due to extreme processing conditions involving large thermo-mechanical stresses and the final mechanical properties of the manufactured part. Various studies attribute the enhanced mechanical properties of Selective Laser Melted (SLM) metallic parts to the formation of cellular dislocation structures, which are usually accompanied by solute segregation to the dislocation cell walls. However, the formation of those cellular structures as well as their effects on the mechanical properties are still poorly understood. Here, we present three-dimensional (3D) discrete dislocation dynamics (DDD) simulations of the dislocation and composition microstructure evolution during SLM manufacturing and their effects on the mechanical properties of 316L stainless steel accounting for solute segregation. These results provide an enhanced understanding of the experimentally observed microstructures and their effect on the mechanical response of SLM manufactured part.
9:10 AM
Microstructural Characterization of Maraging 300 Steel Fabricated by Select Laser Melting: Johnnatan Rodriguez1; Elizabeth Hoyos1; Fabio Conde2; André Jardini Munhoz3; Julian Avila4; 1EIA University; 2University of Sao Paolo; 3BIOFABRIS - National Institute of Science and Technology in Biomanufacturing; 4UNESP – São Paulo State University
Additive manufacturing has been used in different industries like aerospace, medical and automotive. In the aerospace, materials with high performance are needed to fulfill the requirements of the industry. Maraging steels are among the materials widely used due to its high strength and toughness. In this work, a Maraging 300 steel powder was used to produce components by SLM. Two heat treatments were applied to study the martensite-to-austenite reversion, HT1: 480 °C/3 h and HT2: 980 °C/1h + 2x690 °C/5 min + 480 °C/6h. The microstructural characterization was assessed by OM, SEM and EBSD. As-built condition revealed a cellular and dendritic morphology with segregation of Ti, Ni and Mo to the grain boundaries. Direct aging treatment does not erase the typical AM morphology, but a solubilization at 980 °C/1h was capable of fully recrystallize the microstructure. The EBSD analysis showed the increase of reverted austenite for the HT2.
9:30 AM
Recrystallization-based Grain Boundary Engineering of 316L Stainless Steel Produced via Selective Laser Melting: Shubo Gao1; Zhiheng Hu2; Sravya Tekumalla1; Matteo Seita1; 1Nanyang Technological University; 2Singapore Institute of Manufacturing Technology
Applying conventional grain boundary engineering (GBE) processing to near-net-shape parts—including those produced via additive manufacturing (AM) technology—is challenging due to the large mechanical strains involved. In this study, we present an alternative route to GBE, which is based on recrystallization of as-built AM alloys. Focusing on selective laser melting (SLM) of 316L stainless steel (316LSS), we investigate how different combinations of process parameters affect the recrystallization fraction—and thus the twin boundary fraction—in the alloy upon heat treatment. Interestingly, we find that higher laser scanning speed yields higher residual stress, but lower recrystallization fraction. We demonstrate that this surprising result stems from the properties of the cellular structures that form during directional solidification of the alloy, which are also a function of laser scanning speed. Our results provide the groundwork for devising AM-compatible GBE strategies to produce high-performance parts with complex geometry.
9:50 AM Invited
Grain Orientation Analysis of Additively Manufactured 316L Stainless Steel: Anthony Rollett1; 1Carnegie Mellon University
Process variables in additively manufactured (AM) 3D metal print designs can affect their microstructural evolution, texture and defect structures. In particular, variations in laser parameters such as power, velocity and hatch spacing 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 grain growth behavior and orientation evolution. Results obtained from electron backscatter diffraction will be used to visualize and quantify grain growth direction and grain orientation gradients on AM parts built with various laser process parameters.
10:20 AM
Phase Transformation Modeling of Functionally Graded Materials Made by Direct Energy Deposition: Noah Sargent1; Wei Xiong1; Richard Otis2; 1University of Pittsburgh; 2Jet Propulsion Laboratory
Directed Energy Deposition is a powder-based additive manufacturing technique with the advantage of fabricating Functionally Graded Materials (FGMs) through a dynamic variation of composition in consecutive layers along the building direction. FGMs have gained attention for their potential to enhance the performance of components that require a combination of material properties not available in traditional monolithic alloys. Despite the promise of incorporating multifunctional material properties, precipitation of brittle intermetallic phases and microsegregation often lead to undesirable properties. This work aims to address these issues by using the CALPHAD-based ICME (CALPHAD: CALculation of PHAse Diagrams, ICME: Integrated Computational Materials Engineering) method to model solidification, solid-state phase transformations, microsegregation, stacking fault energy, and Martensite start temperature in an FGM from Stainless Steel 316 to High Strength Low Alloy steel. Model-predictions will be compared with experimental results to assess the accuracy of the model developed in this work.
10:40 AM
Effect of Low-temperature Plasma Nitriding on the Wear and Corrosion Resistance of Additive-manufactured Stainless and Maraging Steels: Matjaz Godec1; Črtomir Donik1; Aleksandra Kocijan1; Bojan Podgornik1; Danijela Anica Skobir Balantič1; 1Institute of Metals and Technology
The aim of this work was to investigate whether the same positive effect of nitriding could be obtained for austenitic stainless steel AISI 316 L and maraging steel MS300 that were both additive manufactured using selective laser melting and appropriate heat treatments or aging, selectively, and low-temperature plasma nitriding at different temperatures. This study was designed to better understand the microstructure of additive-manufactured and low-temperature plasma-nitrided surface as well as developing a nitride and a diffusion layer. The comparison of the wear and corrosion resistance, the microhardness and the microstructure changes of the additive-manufactured steels in different post-treated conditions with commercial steels was carried out. It was found that the post-treated low-temperature plasma nitriding improves the wear and corrosion resistance of the additive-manufactured samples. Finally, we were able to explain the microstructures at the nano level as well as correlating the wear and corrosion properties.
11:00 AM
Section Thickness Dependent Behavior in Additively Manufactured Stainless Steel: Thomas Slagle1; Alexandra Vyatskikh1; Sen Jiang1; Salma El-Azab1; Umberto Scipioni Bertoli1; Lorenzo Valdevit1; Enrique Lavernia1; Julie Schoenung1; 1University of California Irvine
In this work, we evaluated the effect of selective laser melting (SLM) process parameters and scan strategy on residual stresses and microstructures of 316L stainless steel parts. We fabricated parts using the NIST AMB2018-01 AM-Bench geometry, and analyzed the microstructure and phase composition as a function of the leg thickness and process parameters. Cooling rates were found to vary threefold (e.g., from ~7x10E5 to ~25x10E5 °C/s) within the same part depending on the leg thickness. In addition, cooling rates were strongly influenced by the scan strategy, with 67° hatch rotation between layers causing ~2x lower cooling rates than 90° hatch rotation. Moreover, higher energy input during printing caused formation of larger surface residual stresses: a ~60% increase in energy input resulted in a ~62% increase in surface residual stress as measured by X-Ray diffraction. Our findings suggest strong relationships between process parameters, part geometries, and resulting microstructures and residual stresses.