Additive Manufacturing: Advanced Characterization with Synchrotron, Neutron, and In Situ Laboratory-scale Techniques: Residual Stress: Neutron, X-ray, and Other Measurements
Sponsored by: TMS: Additive Manufacturing Committee
Program Organizers: Fan Zhang, National Institute of Standards and Technology; Tom Stockman, Los Alamos National Laboratory; Tao Sun, Northwestern University; Donald Brown, Los Alamos National Laboratory; Yan Gao, Ge Research; Amit Pandey, Lockheed Martin Space; Joy Gockel, Wright State University; Tim Horn, North Carolina State University; Sneha Prabha Narra, Carnegie Mellon University; Judy Schneider, University of Alabama at Huntsville
Tuesday 2:00 PM
February 25, 2020
Room: 8
Location: San Diego Convention Ctr
Session Chair: Donald Brown, Los Alamos National Laboratory
2:00 PM Invited
Toward Validation of Residual Stress Predictions in Additively Manufactured Parts: Destructive and Non-destructive Characterization: Kyle Johnson1; Donald Brown2; Bjorn Clausen2; Phillip Reu1; Paul Farias1; Christopher D'Elia3; Michael Hill3; Michael Prime3; Bradley Jared1; Shaun Whetten1; Joseph Bishop1; 1Sandia National Laboratories; 2Los Alamos National Laboratory; 3University of California Davis
Additive Manufacturing (AM) has many potential benefits over traditional manufacturing techniques, such as increased geometric flexibility, rapid prototyping capability, and tailored material properties. However, due to the high thermal gradients present in most AM processes, residual stresses remain a significant issue. Accurate prediction of residual stress profiles is desirable from both a qualification point of view and also to investigate opportunities such as optimized stress profiles. In order for modeling techniques to be trusted, they must be validated with experimental measurements. In this talk, results from multiple experimental methods used to examine residual stress states in as-built Directed Energy Deposition (DED) and Laser Powder Bed Fusion (LPBF) parts are presented and compared to numerical predictions. Experimental methods include non-destructive neutron diffraction as well as destructive methods such as incremental hole drilling. Strengths and weaknesses of the different approaches will also be presented and discussed.
2:30 PM
Neutron-based Research on Additive Manufactured Materials at the Paul Scherrer Institute: Jan Capek1; Efthymios Polatidis1; Manuel Morgano1; Pavel Trtik1; Markus Strobl1; 1Paul Scherrer Institute
Additive manufacturing (AM) is known for the complexity of its processing parameters that greatly influence the materials properties such as porosity, residual stresses, microstructure and mechanical behavior. Neutron-based experimental methods are particularly important for characterizing the bulk material in AM components non-destructively, due to their high penetrability. Synergy of multiscale characterization techniques is applied for studying AM components within the Neutron Imaging and Applied Materials group at the Paul Scherrer Institute. Neutron diffraction studies are undertaken at the instrument POLDI for residual stress characterization and in-situ investigations of the deformation behavior of AM materials. The imaging beamlines ICON and NEUTRA and the novel “Neutron Microscope” are employed for the characterization of the internal structures in length-scales ranging from about 10 microns to cm. Finally, diffraction contrast imaging on the BOA beamline is undertaken for mapping the phase, strain and texture distribution with high spatial resolution.
2:50 PM
Thermomechanical Model Residual Stress Prediction Assessment for Stainless Steel 316L Laser Powder Bed Fusion Components: Nicholas Bachus1; Donald Brown2; Robert Ferencz3; Rishi Ganeriwala3; Michael Hill1; Neil Hodge3; 1University of California Davis; 2Los Alamos National Laboratory; 3Lawrence Livermore National Laboratory
During the additive manufacturing process, residual stress is introduced by the large thermal gradients present in the components as they are built in a layer by layer approach. As we demand additive manufacturing to be more flexible in the pursuit of engineering solutions, we need novel build strategy approaches to control residual stress distributions, as well as models to accurately forecast component characteristics. A set of samples, each with an identical feature built via a distinct protocol are produced, predicted, and evaluated. A total of three samples are produced: the first with a square notch near the build top free surface, the second with the notch built directly above the build plate, and the third with no notch. The residual stress distribution for each sample are predicted by leveraging Lawrence Livermore’s Diablo thermomechanical finite element simulations and compared against neutron diffraction measurements at the Los Alamos SMARTS diffractometer.
3:10 PM
Geometric Influences on Residual Stresses in Components Manufactured by Directed Energy Deposition: Christopher D'Elia1; Michael Hill1; Nicholas Bachus1; Michael Stender1; Christopher San Marchi1; 1University of California, Davis
An assessment of residual stresses that arise naturally in metal additive manufacturing is reported. In additive manufacturing by directed energy deposition (DED), residual stresses develop in components from repeated thermal cycles as each layer is deposited in a series of laser melting paths. Component size and geometry inform laser path planning and influence the local thermal history of material within the additively manufactured component. Rectangular components with various lengths, widths, and heights are fabricated by DED. Residual stresses, at multiple length scales, layer and component scale, are measured in the build direction and build plane using mechanical and diffraction techniques. These measurements are compared to predictions from process simulations within Sandia’s SIERRA computational mechanics code. The simulations also provide information on in-situ strain hardening, which is compared to hardness maps on multiple planes in the builds. The experimental and computational results are interpreted in the context of predicted thermal history.
3:30 PM Break
3:50 PM Invited
Residual Strain Characterization of Additively Manufactured IN625 and 15-5SS
Using Energy Dispersive X-ray Diffraction
: Maria Strantza1; Nicholas Bachus2; Bjorn Clausen2; Thien Phan3; Lyle Levine3; Darren Pagan4; John Okasinski5; Donald Brown2; 1Lawrence Livermore National Laboratory; 2Los Alamos National Laboratory; 3National Institute of Standards and Technologies; 4Cornell High Energy Synchrotron Source; 5Advanced Photon Source
The laser-powder bed fusion additive manufacturing process for metallic parts belong to a novel and innovative production technology. However, understanding and predicting the mechanical response of the produced additively manufactured (AM) components is crucial for engineering applications. The objective of this investigation is to produce high quality residual strain measurements in order to provide input on the controlled benchmark tests (AM-Bench) for AM specimens. In support of this effort, we performed energy dispersive X-ray diffraction measurements on AM Inconel 625 and 15-5 stainless steel components. Our aim is to use the measured lattice parameter to calculate and profile the residual strains on the parts. Our results will be used as a strong validation challenge to modeling agencies. During this presentation, the results on the residual strain along the build and the longitudinal direction will be discussed, as well as the shear residual strain component.
4:20 PM
Advanced Techniques for Characterization of SLM Manufactured Alumina: Malgorzata Makowska1; Kevin Florio2; Stefan Pfeiffer3; Thomas Graule3; Konrad Wegener2; Federica Marone1; Dario Ferreira Sanchez1; Nicola Casati1; Helena Van Swygenhoven1; 1PSI; 2ETH Zurich; 3Empa - Swiss Federal Laboratories for Materials Science and Technology
Applying the Selective Laser Melting (SLM) technology to ceramics is challenging due to not fully understood mechanisms of interaction of the powder with laser light, high melting temperature and low thermal shock resistance. In order to optimize the process, studies of micro- and macrostructure of the ingredient powder and the printed parts are essential. This is achieved by employing advanced synchrotron techniques. The powder used for SLM is composed of alumina granules spray-dried from a mixture of 3-sizescales of Al2O3 particles doped with metal oxide nanoparticles. The composition and crystallographic structure of the granules and printed parts is studied by means of combined micro-XRD/micro-XRF 2D and 3D imaging (microXAS, PSI) and high-resolution powder diffraction (MS beamline, PSI). These studies demonstrated a uniform dopant distribution in as-produced alumina granules and capability to modify it prior to laser treatment. Quantitative analysis of porosity and cracks is performed by synchrotron tomography (TOMCAT, PSI).
4:40 PM
Microscale Residual Stresses in Additively Manufactured Stainless Steel: Yin Zhang1; Ting Zhu1; Wen Chen2; Morris Wang3; 1Georgia Institute of Technology; 2University of Massachusetts, Amherst; 3Lawrence Livermore National Laboratory, Livermore
Additively manufactured (AM) metallic materials commonly possess substantial microscale internal stresses. However, the impact of these residual stresses on the mechanical behaviour remains largely unexplored. Here we combined in-situ synchrotron X-ray diffraction (SXRD) experiments and computational modelling to quantify the lattice strains in different families of grains with specific orientations and associated residual stresses in AM 316L stainless steel. The results reveal the effects of elastic anisotropy, progressive yielding and work hardening on the behaviours of lattice strains. We also measured pronounced tension-compression asymmetries in yield strength and work hardening. Such asymmetries are associated with the back stresses that originate from heterogeneous dislocation distributions and resultant intragranular residual stresses. Furthermore, stress-relief heat treatment was shown to reduce the tension-compression asymmetries as well as the magnitude and non-linearity of lattice strains. This work establishes the mechanistic connections between the microscale residual stresses and mechanical behaviour of AM stainless steel.
5:00 PM
Investigating Local Microstructural Response During Short Fatigue Crack Growth in SLM IN718 Subjected to High Cycle Fatigue Loading: Priya Ravi1; Diwakar Naragani1; Jun-Sang Park2; Peter Kenesei2; Michael Sangid2; 1Purdue University; 2Argonne National Laboratory
Additive manufacturing (AM) has gained immense popularity over the past decade due to its advantages over the conventional manufacturing methods. However, the performance of AM parts in fatigue and fracture critical applications is still uncertain. This study explores the short fatigue crack growth (SFCG) mechanisms in AM Inconel 718 using in situ high-energy diffraction techniques. The evolution of the 3D microstructure and grain-averaged stresses in the vicinity of a propagating crack as well as delayed crack opening was captured during loading. The SFCG was observed to follow a mixed mode style of propagation (mode I opening and mode II shear), which were analyzed via the alignment of the crack growth direction with the stress state experienced in the grains ahead of the crack tip, such as maximum principal stress, resolved shear stress (RSS), and normal stress to the plane experiencing the maximum RSS.