Additive Manufacturing: Alloy Design to Develop New Feedstock Materials: Session I
Sponsored by: TMS: Additive Manufacturing Committee, TMS: Alloy Phases Committee
Program Organizers: Joseph McKeown, Lawrence Livermore National Laboratory; Aurelien Perron, Lawrence Livermore National Laboratory; Manyalibo Matthews, Lawrence Livermore National Laboratory; Christian Leinenbach, Empa, Swiss Federal Laboratories for Materials Science and Technology; Peter Hosemann, University of California, Berkeley
Wednesday 8:00 AM
November 4, 2020
Room: Virtual Meeting Room 4
Location: MS&T Virtual
Session Chair: Christian Leinenbach, Empa; Manyalibo Matthews, LLNL
8:00 AM Invited
High-Throughput Accelerated Alloy Development: Kenneth Vecchio1; Olivia Dippo1; 1University of California, San Diego
To accelerate alloy development, we designed an integrated, high-throughput method focused on parallelizing, miniaturizing, and automating each step: sample synthesis, preparation, characterization, and analysis. In this method, alloy test samples are built using laser metal deposition in 15-sample libraries that facilitates rapid and automated characterization by XRD, EDS, and EBSD. These analyses are coupled with machine learning to accelerate subsequent composition and processing decisions. We demonstrate this method for conventional alloy modification and to design a functionally graded material from 316L stainless to Ti-6Al-4V, without forming brittle intermetallic compounds. To mitigate intermetallic formation, a CALPHAD-based alloy design algorithm was developed to calculate phases formed and create a gradient path from 316L to Ti-6Al-4V, utilizing a third alloy as an additive. A sample library of discrete steps along the gradient alloy path have been printed and characterized to gain full understanding of microstructure development and develop a crack-free graded material.
8:30 AM Invited
Accidental Alloy Development: In-situ Evolution of AM Powder and Opportunities for New Material Synthesis Pathways: Tim Horn1; Chris Rock1; 1North Carolina State University
During powder bed Additive Manufacturing (AM) metallic powders interact with directed energy sources such as laser or electron beam, varying partial pressures of process gasses, vaporized/condensed material, plasma and ejected liquids. This results in morphologies, compositions, and phases not observed in as-atomized feedstocks. Localized concentrations on the scale of powder and the melt pool have a profound impact on solidification, local composition, microstructure evolution, solid-state phase transformations and subsequently properties in surprising and unexpected ways. This is further complicated by AM thermal cycling which can form far-from-equilibrium interfaces. While this creates an additional level of complexity towards understanding, and is typically considered a shortcoming of AM to be eliminated, it also motivates research to elucidate these mechanisms and create new tools for the intentional interfacial control of these effects for exploitation of newly emerged properties. We will present several recent case studies of unique material interactions in LPBF/EB-PBF AM.
9:00 AM
Characterization of Spatter with Organized Features in Laser Powder Bed Fusion: Christopher Rock1; Tim Horn1; 1North Carolina State University
Spatter observed in laser powder bed fusion has different particle morphologies, sizes and features specific to its formation mechanism and alloy composition. However, it has been observed that organized features on selected spatter particles, such as lens shaped spots and related surface configurations, have similarities among different alloy systems used in PBF. This research characterizes spatter with organized surface features across multiple alloy systems and develops a hypothesis for its formation.
9:20 AM Invited
Optimization of Nitrogen-Atomized 17-4 Stainless Steel Feedstock for AM Processing: Carelyn Campbell1; James Zuback1; Mark Stoudt1; 1National Institute of Standards and Technology
Wrought martensitic precipitation hardened stainless steel, 17-4 PH, is widely used in the aerospace and marine industries when high strength and corrosion resistance are needed. Additively manufactured (AM) nitrogen-atomized 17-4 parts often have unexpected properties that result in poor performance, primarily as the nitrogen acts as an austenite stabilizer and the desired martensitic matrix microstructure is not achieved. This work focuses on optimizing the feedstock composition within the composition specification to control the influence of the nitrogen on the AM part. The current alloy specification allows for significant composition variation in the Cr, Ni, Cu, and Nb contents. The Cr and Ni contents are optimized with respect to the solubility of nitrogen at the processing temperatures and influence on the martensitic start temperature. The Cu and Nb contents are optimized to maximize the precipitation strengthening during aging. The models are validated using experimental results from AM nitrogen-atomized powder 17-4 parts.
9:50 AM
Sensitivity Analysis and Composition Design for Metal Additive Manufacturing Using CALPHAD-based ICME Framework: Xin Wang1; Soumya Sridar1; Wei Xiong1; 1University of Pittsburgh
During powder manufacture for metal additive manufacturing, the final composition will deviate from the designed composition, which may lead to undesired properties in the printed part. It is critical to perform an uncertainty quantification during alloy design to identify a proper composition range that meets all property requirements. In this work, we developed a CALPHAD-based ICME framework (CALPHAD: calculations of phase diagrams, ICME: integrated computational materials engineering) to optimize the composition and perform uncertainty quantifications, using high-strength low-alloy (HSLA) steel as a case study. Critical properties, such as impact transition temperature, yield strength, and printability were evaluated. With the same uncertainty as initial composition, a new nominal composition was determined, and it increased the probability of successful builds by 47%. Feedstock produced based on the designed composition was printed and systematically characterized. The printed samples exhibited high room temperature strength, good printability, and excellent toughness at -20°C.
10:10 AM Invited
Laser Additive Manufacturing of Nanocomposite Powders: Bilal Gokce1; Stephan Barcikowski1; 1University of Duisburg-Essen
During the past few years laser synthesis and processing of colloids (LSPC) has been established as an economically feasible synthesis method that addresses real-world problems. In this contribution, we show that by pH-controlled, colloidal adsorption of laser-generated nanoparticles on metal powders we are able to produce new composite materials that are highly relevant for powder-based 3D-printing methods such as laser powder bed fusion (LPBF). These composite powders contain a homogeneous distribution of nanoparticles on its surface. Due to the barrier-free surface of the small, highly dispersed colloidal nanoparticles, a high surface coverage can be achieved even with mass loadings of 0.1wt%, as will be shown for Y2O3 nanoparticles supported on steel powder that is used as feedstock for LPBF of ODS steels. Studies on L-PBF-built parts show that the homogeneity of the surface coverage can be transferred to the metal alloy part.
10:40 AM
Residual Stress Mitigation of Additive Manufactured Stainless Steel 316L Components through the Directed Energy Deposition Inclusion of TiC Nanoparticles: Jakob Hamilton1; Samantha Sorondo1; Andrew Greeley1; Denis Cormier1; Iris Rivero1; 1Rochester Institute of Technology
Directional solidification in directed energy deposition (DED) additive manufacturing (AM) often leads to detrimental residual stresses (RS) and thermal distortion in as-fabricated components. Residual stresses exacerbate cyclic loading and reduce the fatigue life of DED components. Recent efforts to mitigate residual stresses in DED include altering deposition parameters and inclusion of ceramic reinforcements. These particles act as nucleation sites and disrupt columnar grain growth from rapid material solidification. This work explores how the inclusion of TiC nanoparticles in the build of stainless steel 316L AM components affects RS distribution. Nondestructive residual stress measurement through x-ray diffraction yielded that components possessing TiC nanoparticles exhibited compressive residual stresses near TiC agglomerates. Likewise, the TiC distribution was found to depend on DED parameters, thus providing a method to affect residual stress patterns in AM metal composite components. This work quantifies modification of residual stresses in AM through the direct inclusion of TiC nanoparticles.