Additive Manufacturing of Metals: Establishing Location-Specific Processing-Microstructure-Property Relationships: Advances in Methods, Characterization, and Modeling Tools
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: High Temperature Alloys Committee, TMS: Shaping and Forming Committee, TMS: Additive Manufacturing Bridge Committee
Program Organizers: Eric Lass, NIST; Judy Schneider, University of Alabama-Huntsville; Mark Stoudt, National Institute of Standards and Technology; Lee Semiatin, AFRL; Kinga Unocic, Oak Ridge National Laboratory; Joseph Licavoli, Michigan Technological University; Behrang Poorganji, YTC America Inc.

Tuesday 2:00 PM
February 28, 2017
Room: 7B
Location: San Diego Convention Ctr

Session Chair: Lee Semiatin, AFRL; Ayman Salem, Materials Resources LLC

2:00 PM  Invited
Cloud-based Integrated Computational Microstructure-informed Response for Titanium Additive Manufacturing: Ayman Salem1; Daniel Satko1; Joshua Shaffer1; Richard Kublik1; Mohsen Seifi2; John Lewandowski2; S.L. Semiatin3; 1Materials Resources LLC; 2Case Western Reserve University; 3Air Force Research Laboratory
    Location-specific mechanical response in parts made by additive manufacturing (AM) of titanium alloys (e.g., Ti-6Al-4V and -TiAl) is directly related to the underlying location-specific microstructure. The inherent variability in AM processing results in a spatial variability of microstructure constituents including defects as well as the morphology and crystallography of various phases. Microstructure quantification using traditional single-point statistics (e.g. average lath thickness and distribution) does not account for such variability. Alternatively, higher-order statistics (e.g., 2-point correlations) provide robust quantification of microstructure heterogeneities. However, its wider use among designers and manufacturers is hindered by the unavailability of the tools and the need to exchange massive microstructure data. This talk will summarize an effort to address both issues and enable microstructure-informed designs using cloud computing (MiCloud.AM) of AM parts made by powder-bed-fusion (PBF).

2:30 PM  Invited
Understanding Structure Property Relationships in Electron Beam Melting through Data Analytics and Visualization: Ryan Dehoff1; Vincent Paquit1; Michael Kirka1; Ralph Dinwiddie1; Kinga Unocic1; Peeyush Nandwana1; Sean Yoder1; Naren Ragav2; William Halsey1; Chad Steed1; Suresh Babu1; 1Oak Ridge National Laboratory; 2University of Tennessee
    Electron Beam Melting (EBM) is a powder bed Additive Manufacturing (AM) technology for the creation of 3D parts from metal powders. Although the process has demonstrated the ability to fabricate complex geometries that are difficult to create with conventional manufacturing technologies, the process-structure-property relationships are still not well understood. This work focuses on the development and application of both 2 and 3-dimensional data visualization and data analysis tools for determining process parameter and geometrical influence on the resulting microstructure and mechanical properties of materials. Specific tools for visualizing data include DREAM3D, EDEN, and FALCON. These tools allow for tracking processing parameters (beam current, speed, etc.), modeling data, in-situ process monitoring data such as near infrared and infrared data, post inspection information (microstructure, x-ray CT, microstructure) and mechanical properties across multiple layer or builds. Specific examples using Ti-6Al-4V and Inconel 718 will be discussed.

3:00 PM  
Three-dimensional Tomography of EBM-manufactured IN718: Andrew Polonsky1; McLean Echlin1; William Lenthe1; Ryan Dehoff2; Michael Kirka2; Tresa Pollock1; 1University of California, Santa Barbara; 2Oak Ridge National Laboratory
    Electron Beam Melting (EBM) is an additive manufacturing technique that enables the fabrication of geometrically complex components in near-net shape. Process parameters employed to build additive parts result in a wide range of microstructural features and defects as compared to traditional wrought parts, limiting the structural properties of these manufactured components. The TriBeam, a femtosecond laser-based tomography technique, was employed to obtain chemical, structural, and crystallographic data on mm-scaled representative volumes of EBM-manufactured Inconel alloy 718. TriBeam tomography was used to analyze the segregation of secondary phases in relation to lack of fusion and porosity defects. The three-dimensional grain structure and crystallographic texture that result from solidification of the melt pool during EBM processing will also be discussed.

3:20 PM  
High Strain Rate Mechanical Behavior of Stainless Steel 316L Processed by Selective Laser Melting: Travis Kneen1; Christopher Barrett1; Brett Conner1; Guha Manogharan1; 1Youngstown State University
    This presentation is a study on stainless steel 316L AM parts processed in a Selective Laser Melting (SLM) machine under two different sets of process parameters in multiple build orientations. Microstructural characterization, dynamic, impact, and quasi-static strain rate mechanical tests were conducted to analyze the as-fabricated AM mechanical properties when compared to wrought 316L. It was found that laser scanning speed and point difference were critical parameters that affected the microstructure and mechanical properties. It was observed that during quasi-static loading that specimens from both sets of AM process parameters had a higher yield strength when compared to wrought specimens. At strain rates of 10^3/s, both SLM produced 316L and wrought 316L showed strain rate sensitivity (hardening), but this effect was more pronounced in the wrought material. The influence of build orientation was also found to impact the overall results for both sets of SLM process parameters.

3:40 PM Break

4:00 PM  Invited
Recent Progress in Low-cost Open-source Metal 3-D Printing: Joshua Pearce1; Paul Sanders1; 1Michigan Tech
    The open-source release of the self-replicating rapid prototyper (RepRap) 3-D printer design enabled an explosion of innovation and access to additive manufacturing technology. This work was primarily limited to polymers, however, by augmenting RepRap 3-D printer designs a low-cost metal 3-D printer utilizing gas metal arc welding (GMAW) technology was developed. These designs have matured with integrated open source electronic monitoring and control systems, as well as porting the concept to augmented CNC router tables. This enables small businesses and even individuals to print 3-D objects in metal. Initial work to characterize the porosity, hardness, and ultrasonic moduli of steel and aluminum parts produced found mechanical properties similar to the bulk wrought material. Additional mechanical properties tests have been undertaken to optimize processes for conventional alloys in GMAW-based 3-D printing and to identify 3-D printing-specific alloys and approaches for improved resolution. Recent progress in this burgeoning field will be reviewed.

4:30 PM  
The Effect Process Parameters have on Residual Stress and Texture of Additively Manufactured Ti-6Al-4V Components: Nathan Levkulich1; Gregory Loughnane1; Nathan Klingbeil1; 1Wright State University
    Laser powder bed fusion processes are typically characterized by extremely high cooling rates and thermal gradients, often resulting in undesirable residual stress. Both nondestructive (X-ray diffraction (XRD)) and semi-destructive (hole drilling) techniques are used to estimate principal stresses in additively manufactured components. XRD is used to measure residual stress on the surfaces Ti-6Al-4V as-built components, while the hole drilling technique is leveraged to investigate stress variations throughout the depth of each component. Various methods for preparing substrates, including grit-blasting, milling, grinding, and heat treating are also reviewed via XRD. Finally, Knoop hardness measurements are compared with the material texture observed in electron back-scatter diffraction imaging (e.g., inverse pole figures, inverse pole figure maps), and these findings are correspondingly correlated to residual stress.

4:50 PM  
Synchrotron X-ray and Neutron Diffraction Measurements of Multi-scale Full Tensor Residual Stresses in Nickel-based Super Alloy Built through Direct Metal Laser Sintering Technique of Additive Manufacturing: Thien Phan1; Lyle Levine1; Thomas Gnaeupel-Herold1; Yaakov Idell1; 1National Institute of Standards and Technology
    While the direct metal laser sintering technique of additive manufacturing allows for the fabrication of parts with complex shapes, large residual stresses are present in the as-built condition due to localized rapid heating and solidification. Stresses at the macroscopic length scale can result in dimensional tolerance issues as well as detrimental effects on mechanical properties. At the submicron length scale, residual stresses provide the driving force for microstructure evolution and grain growth. Thus, post-build heat treatments are used to relieve these residual stresses. To study the effectiveness of the heat treatment in our goal to obtain an optimized microstructure, the residual stresses of as-built and heat treated Inconel 625 samples were assessed. Depth-resolved microbeam synchrotron X-ray diffraction was used to determine the full elastic strain and residual stress tensors from sub-micrometer volumes within Inconel 625 samples; meanwhile, neutron diffraction was used to determine residual stresses at the millimeter length scale.

5:10 PM  
Study on the Effects of Microsegregation, Temperature, and Stress on IN625 Microstructures by Phase Field Simulations: Trevor Keller1; Jonathan Guyer1; 1National Institute of Standards and Technology
    High levels of microsegregation near melt pool boundaries promotes precipitation of deleterious phases in additively manufactured parts. It is desirable, at a minimum, to limit growth of such particles during post-processing. While Ni-based superalloys are chemically and microstructurally complex, a minimally representative model has been implemented using the phase field method with contributions from diffusion and solid state phase transformations with misfit and residual stress. Initial conditions for the simulations are informed by experimental characterization of additively manufactured Ni-based superalloy parts using electron and X-ray techniques. The effects of microsegregation and residual stress on deleterious particle evolution will be discussed for representative isothermal heat treatments.