Additive Manufacturing of Metals: Applications of Solidification Fundamentals: Solidification of Advanced Materials II
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Additive Manufacturing Committee, TMS: Solidification Committee
Program Organizers: Wenda Tan, The University of Michigan; Alex Plotkowski, Oak Ridge National Laboratory; Lang Yuan, University of South Carolina; Lianyi Chen, University of Wisconsin-Madison
Thursday 8:30 AM
March 23, 2023
Room: 21
Location: SDCC
Session Chair: Lang Yuan, University of South Carolina; Lianyi Chen, University of Wisconsin-Madison
8:30 AM
Improving Ductility of 316L Stainless Steel by Inducing Melt Pool Instability in Directed Energy Deposition: Lin Gao1; Wenhao Lin1; Zhongshu Ren1; Ma Ji1; Tao Sun1; 1University of Virginia
Developing effective printing strategies to fabricate structural materials with superior mechanical performance is an active research area in metal additive manufacturing (AM). In our work, we applied a wiggle deposition pattern in wire laser-directed energy deposition of 316L stainless steel. The as-built sample exhibits much-improved ductility without compromise of strength. Using multi-physics simulation, operando near-infrared imaging and synchrotron X-ray diffraction, we discovered that the wiggle deposition pattern induces highly dynamic melt flow and oscillating thermal gradient in the melt pool, which interrupts the directional grain growth in the mushy zone and generates considerable grain boundary (GB) protrusions (a.k.a. serrated GBs). This unique GB structure can accommodate intergranular deformation, and therefore improve the tensile property of the sample. We believe the fundamental principle of inducing melt pool instability can be readily implemented in other metal AM processes to further expand the classical strength–ductility envelope of conventional and emerging alloys.
8:50 AM
Interface Characteristics of a 2205 Duplex Stainless Steel Processed by Laser Powder Bed Fusion Additive Manufacturing: Nima Haghdadi1; Hansheng Chen2; Zibin Chen3; Sudarsanam Babu4; Xiaozhou Liao2; Simon Ringer2; Sophie Primig1; 1UNSW Sydney; 2University of Sydney; 3The Hong Kong Polytechnic University; 4University of Tennessee, Knoxville
Thermal gyrations during metals additive manufacturing (AM) may lead to microstructural complexities, particularly at interfaces. In this study, using advanced characterization techniques, we unveil some of such phenomena in a duplex stainless steel processed by laser powder bed fusion. For the austenite-ferrite interfaces, ferrite grains are shown to have a higher tendency to terminate on (100) habit planes instead of crystallographically and energetically favoured (110) planes. This is due to the character of parent ferrite-ferrite boundaries, dictated by the sharp <100> texture, and the geometry of austenite grains, enforced by directional solidification and epitaxial growth of ferrite in AM. We also report local fluctuations in Fe and Cr contents in regions adjacent to ferrite-ferrite grain boundaries, providing Cr-rich precursors for Cr2N formation. This is believed to be due to increased thermal gyrations and stresses associated with AM, triggering non-equilibrium grain boundary segregation.
9:10 AM
Microstructural Control of a Multi-Phase PH Steel Printed with Laser Powder Bed Fusion.: Brandon Fields1; Diran Apelian1; Lorenzo Valdevit1; 1University of California Irvine
The microstructure and properties have been observed to vary substantially in different locations of laser powder bed fusion parts. This variation is due to local changes in cooling rates and thermal gradient direction when varying the part geometry. Understanding and controlling this phenomenon is crucial towards optimizing the properties of a printed part. This microstructural control can be utilized when applied to a material which has differing phases with distinct advantageous properties (such as strong & brittle versus weak & ductile), that can be tuned locally to optimize the overall part. We demonstrate this understanding and control in a dual phase 17-4 precipitation hardened steel, quantify the differences in mechanical properties between the microstructures, and determine the ability and scale of microstructural control. Control of local and bulk properties by tuning the microstructure are observed.
9:30 AM
Origin of Epitaxy Loss in Laser Powder Bed Fusion: Prosenjit Biswas1; Ji Ma1; 1University of Virginia
Although the epitaxial growth from the substrate dominates the initial grain development during laser powder bed fusion, epitaxial solidification is lost quickly after a small transition region on the order of <1 to several layer thickness, based on processing conditions and substrate texture. This study examines the texture transition mechanism and the condition that leads to a larger transition region. Two SS316L samples with different printing speeds were printed on an SS316L Single Crystal substrate. The misorientation analysis from the cellular-solidification features and the EBSD map shows that the misorientation accumulates from the meltpool boundary to the center to accommodate for the change in local temperature gradient direction towards the meltpool center. This misorientation continuously accumulates from layer to layer, starting from the substrate, contributing to a large discontinuous jump, once reaches 12°~15°, to form a completely new grain. The rate of accumulation is inversely proportional to scan speed.
9:50 AM
Phase Transformation Pathways and Solute Behaviour at Boundaries in Ti-6Al-4V Manufactured via Electron Beam Powder Bed Fusion: William Davids1; Andrew Breen1; Simon Ringer1; 1The University of Sydney
Additively manufacturing Ti-6Al-4V involves a complex combination of phase transformations, leading to microstructural, property and solute heterogeneity within a single as-fabricated build. Here, we study (i) the phase transformation pathway specific to Ti-6Al-4V manufactured via electron beam-powder bed fusion, and (ii) its implication on the solute distribution at all unique Burgers orientation relationship boundaries. We reveal that the high-temperature β phase can be separated into two categories, depending on whether it was retained from cooling from above the β transus temperature, or nucleated below it. This insight was enabled via the development of novel post-processing techniques. We use correlative transmission Kikuchi diffraction and atom probe tomography to show the heterogeneous nature of V, Fe and Al across the interface plane, and quantify their interfacial excess w.r.t misorientation across each unique boundary type. While this study concerns E-PBF Ti-6Al-4V, it is a first for the alloy in general.
10:10 AM Break
10:25 AM
Process-Structure-Property Relationship in Selective Laser Melting of 18Ni-300 Maraging Steel: Tianyi Lyu1; Sagar Patel2; Yu Zou1; 1University of Toronto; 2University of Waterloo
Selective laser melting (SLM) of 18Ni-300 maraging steel has gathered considerable popularity in both industries and academia. Nevertheless, there lacks a comprehensive paradigm that correlates the process parameters, microstructure, and mechanical properties of as-built maraging steel. In this study, defect-free maraging steel samples are successfully fabricated under three melting modes (i.e., keyhole, transition, and conduction) with significantly different energy inputs. Microscopic characterization and mechanical tests reveal subtly different microstructures caused by initial solidification and cyclic reheating, as well as correspondingly distinct mechanical performances. The results bring insights into the thermophysical phenomena taking place at the melt pool during the printing process and serve as theoretical foundations for SLM of microstructural graded maraging steel.
10:45 AM
Phase Selection of Intermetallic Compounds for an Al-10Ce-8Mn (wt.%) Alloy: Kevin Sisco1; Suresh Babu1; Alex Plotkowski2; 1University of Tennessee Knoxville; 2Oak Ridge National Laboratory
Additive manufacturing allows the ability to control the thermal gradient (G) and solidification velocity (V) at each voxel in a part. Using the G and V from thermal models we can implement the interface response function (IRF) discussed by Kurz and Trivedi. The IRF can be modified to directly compute thermodynamic terms from Gibbs free energy databases, which allow the undercooling of a phase to be determined. With the development of new aluminum alloys, such as Al-10Ce-8Mn (wt.%), the ability to determine phase selection can assist in selecting a desirable microstructure. Solidification phase selection can manipulate the mechanical properties and microstructure stability of an alloy. There are challenges yet to be addressed including the stoichiometry of intermetallic phases. In this talk, the Al-10Ce-8Mn system is used as a template for discussion because of the ability to manipulate the primary solidification phases: Al10Mn2Ce, Al20Mn2Ce, and a eutectic FCC Al + Al20Mn2Ce.
11:05 AM
Solidification-Microstructure Relationship Study of Single-track Laser Scanned Mg-RE Alloys: Wan Ye1; Aijun Huang1; Yuman Zhu1; Robert Wilson2; Kun Yang2; 1Monash University; 2The Commonwealth Scientific and Industrial Research Organisation
Magnesium (Mg) is the lightest structural metal and its high specific strength makes it competitive in weight-sensitive applications. It is difficult to manufacture complex-shaped parts with internal structures via conventional manufacturing. Hence, additive manufacturing (AM), a net-shape technology with high cooling rate nature, became an attractive fabrication method for Mg alloys. While there has been some work in additive manufactured Mg alloys, the solidification-microstructure-mechanical property relationship is still incomplete. In this work, single-tracked laser scans with various linear energy inputs were applied to Mg-RE (rare earth) alloys. It showed that different scanning parameters and RE additions can both tune the grain structures to columnar or equiaxed. Besides, a refined cellular structure and cellular structure morphology transition could be observed. The work aims at understanding the formation mechanisms of the different grain structures and cellular structures and illustrating the effect of both scanning parameters and RE additions.
11:25 AM
Alleviate Hot Cracking for Nickel-based Superalloys in Additive Manufacturing: Zhongji Sun1; Yan Ma2; Dirk Ponge2; Stefan Zaefferer2; Eric Jägle3; Baptiste Gault4; Anthony Rollett5; Dierk Raabe2; 1Max-Planck-Institut für Eisenforschung GmbH, Institute of Materials Research and Engineering, A*STAR, Singapore; 2Max-Planck-Institut für Eisenforschung GmbH; 3Universität der Bundeswehr München; 4Max-Planck-Institut für Eisenforschung GmbH, Imperial College London; 5Carnegie Mellon University
Nickel-based superalloy is an indispensable alloy group for high-temperature applications. However, most of the nickel-based superalloys suffer from solidification/hot cracking during the additive manufacturing process. Aided by the near-atomic scale characterisation through atom probe tomography, the elemental partitioning information during solidification was successfully captured. Subsequent interpretation using thermodynamic Calphad calculations shedded light on the origin of cracking for this material class. Effects of individual element towards hot cracking are quantified using a commercial IN738LC alloy as an example. Solutions to the hot cracking issue in nickel-based superalloys are then conceptualised and validated.