6th International Congress on 3D Materials Science (3DMS 2022): Additive Manufacturing II: Deformation Mechanisms
Program Organizers: Dorte Juul Jensen, Technical University of Denmark; Marie Charpagne, University of Illinois; Keith Knipling, Naval Research Laboratory; Klaus-Dieter Liss, University of Wollongong; Matthew Miller, Cornell University; David Rowenhorst, Naval Research Laboratory
Tuesday 9:30 AM
June 28, 2022
Room: Capitol A
Location: Hyatt Regency Washington on Capitol Hill
Session Chair: Patrick Callahan, US Naval Research Laboratory
9:30 AM Invited
Characterization of Microstructures and Deformation Mechanisms in Additively Manufactured 316L Stainless Steels: Jean-Baptiste Forien1; Nicolas Bertin1; Tatu Pinomaa2; Anssi Laukkanen2; Kirubel Teferra3; Margaret Wu1; Marissa Linne1; Sylvie Aubry1; Nathan Barton1; Y. Morris Wang4; Thomas Voisin1; 1Lawrence Livermore National Laboratory; 2VTT Technical Research Center of Finland; 3US Naval Research Laboratory; 4University of California Los Angeles
Rapid thermomechanical cycles during laser powder-bed-fusion (L-PBF) additive manufacturing (AM) gives as-fabricated metals none-equilibrium microstructures, most often resulting in improved properties. In L-PBF 316L stainless steels (316LSS), this means breaking off the strength/ductility tradeoff. So-called cellular structures have explained the significant increase in strength. However, these structures are complex, with high density dislocation cells containing precipitates and trapped solutes. We will present our recent investigations of the plasticity of L-PBF 316LSS, first introducing the multi-scale microstructural features present in the as-fabricated and annealed materials. The second part will focus on how we test, characterize, and simulate the plastic deformation of L-PBF 316LSS materials, with and without post-process heat treatment. We use electron microscopy (SEM and TEM), in-situ high energy X-ray diffraction (HEXRD), cellular automata, 3D crystal plasticity simulations, and 3D virtual HEXRD. This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344.
10:00 AM
Evaluation of an Improved Void Descriptor Function to Uniquely Characterize Three-dimensional Pore Networks and to Predict Failure Location in Additively Manufactured Metals: Dillon Watring1; Jake Benzing2; Orion Kafka2; Li-Anne Liew2; Newell Moser2; John Erickson3; Nikolas Hrabe2; Ashley Spear3; 1Naval Research Laboratory; 2National Institute of Standards and Technology; 3University of Utah
Subtle differences among additive manufacturing process parameters lead to variations in three-dimensional pore networks and complicate the prediction of void-sensitive mechanical behaviors. The current work expands upon a recently developed pore metric, the void descriptor function (VDF), by accounting for interactions among three-dimensional neighboring pores and stress concentrations induced by non-spherical pores. The modified VDF is evaluated against 120 computationally generated fracture simulations and six physical mesoscale tensile specimens of as-built laser powder bed fused IN718. The latter set of experiments, which include X-ray computed tomography measurements, enables evaluation against pore populations that are representative of three-dimensional defects commonly observed in AM metals. In the experimental data set, the modified VDF accurately predicts the location of fracture in five out of six specimens compared to only two out of the six for the original VDF. This improved function enables accurate predictions of fracture locations in AM metals.
10:20 AM
Application of 3D Characterization for Mechanical Modelling of Additively Manufactured AlSiMg: Andrew Polonsky1; Thomas Ivanoff1; Nathan Heckman1; Kyle Johnson1; 1Sandia National Laboratories
Additive Manufacturing (AM) offers enhanced flexibility of design for complex engineered components, enabling the fabrication of geometries otherwise inaccessible to conventional manufacturing processes. Application of AM components for critical applications, however, has largely been limited due to the variability observed in mechanical response and the stochastic nature of failure in these parts. Here we present the application of conventional and three-dimensional (3D) microstructural characterization of samples of AM AlSiMg to validate and improve modelling approaches to predict mechanical response in AM materials. In situ computed tomography (CT) loading experiments reveal the role of defects and surface artifacts inherent to the manufacturing process. Given a well-calibrated material model, a finite element modelling framework can accurately predict failure in these AM parts. The sensitivity of the modelling framework to mesh size, as well as it’s extensibility to larger-scale, real-world components will also be discussed.
10:40 AM Break
11:00 AM
Plateau-Rayleigh Instability with a Grain Boundary Twist: Omar Hussein1; Keith Coffman2; Shen Dillon3; Fadi Abdeljawad1; 1Clemson University; 2University of Illinois Urbana-Champaign; 3University of California, Irvine
High-precision manufacturing techniques have enabled the fabrication of three-dimensional materials architectures with intricate nanoscale features, including nanolattices and nanowires. However, the microstructural stability of such nanoscale morphologies remains poorly understood. Recent experimental findings have revealed a morphological instability, in which polycrystalline nanoscale rods/ligaments break up into spatially isolated structures; a behavior that is reminiscent of the Plateau-Rayleigh instability observed in liquids. Here, we present a theoretical and a 3D Phase-Field computational studies to investigate the mechanisms controlling such pinch-off instabilities in polycrystalline nanoscale morphologies. An analytical model is used to derive a stability surface in terms of grain boundary and free surface energies, which demarcates stable and unstable perturbations. Computational studies are used to reveal self-similar scaling describing the critical time to pinch-off. In broad terms, our results show that the thermodynamic and kinetic aspects of this nanoscale instability in solids are mechanistically different from the classic Plateau-Rayleigh model.
11:20 AM
Understanding the Influence of Porosity and Defects on
Mechanical Behavior in Additive Manufactured 316L Stainless Steel Using
In-situ X-ray Computed Tomography: Aeriel Murphy-Leonard1; Dave Rowenhorst1; Richard Fonda1; 1Naval Research Laboratory
Three-dimensional techniques such as x-ray micro-computed tomography (XCT) enable the ability to fully visualize and quantify porosity and provide fundamental relationships between pore size and morphology on mechanical behavior and damage evolution. In the current study, the influence of pore and void size, morphology, and distribution on crack initiation, growth, and coalescence during tensile and cyclic loading was examined using a lab based XCT system and in-situ synchrotron XCT. The material examined was additively manufactured (AM) 316L stainless steel. The specimens were produced using laser powder bed fusion techniques where the gauge diameter was 1 mm. Static XCT revealed that in conditions where the cross-sectional area is small majority of the porosity was in-homogeneously distributed where a higher distribution of porosity was found near the surface which is commonly seenin additively manufactured materials. It was also determined that cracks initiated at near surface defects in the specimen during fatigue.