Additive Manufacturing of Metals: Establishing Location-Specific Processing-Microstructure-Property Relationships: Local Microstructural Control and Graded Materials
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 8:30 AM
February 28, 2017
Room: 7B
Location: San Diego Convention Ctr

Session Chair: Mark Stoudt, NIST; John Lewandowski, Case Western Reserve University

8:30 AM  Invited
Location- and Orientation-dependent Properties in AM Systems: John Lewandowski1; 1Case Western Reserve University
    The talk will review recent collaborative work where both location- and orientation-dependent properties have been obtained in Ti-6Al-4V produced via EBM in both as-deposited and HIP conditions. Microstructure characterization has been conducted via EBSD while defect distribution has been quantified via tomography. The effects of build orientation, test location, machine generation, and subsequent post processing on the mechanical behavior of EBM Ti-6Al-4V will be demonstrated.

9:00 AM  Invited
Development of Ti-6Al-4V to 304L Stainless Steel Functionally Graded Components Fabricated with Laser Deposition: R. Peter Dillon1; John Paul Borgonia1; Ashley Reichardt2; Bryan McEnerney1; Andrew Shapiro1; Peter Hosemann2; 1Jet Propulsion Laboratory; 2University of California, Berkeley
    High integrity joints between Ti-alloys and austenitic stainless steels are highly sought after in the aerospace, nuclear, and other industries. However, they continue to present a problem for both fusion and non-fusion welding techniques due to cracking, unwanted residual stresses, and poor bend ductility resulting from brittle FeTi intermetallic formation. In contrast to most welding techniques, laser deposition allows for the fabrication of components and joints in which composition can be varied gradually layer by layer. This allows a path from one alloy to another to be strategically chosen to avoid unfavorable regions of composition space. Using this technique, several components transitioning from Ti-6Al-4V to 304L SS were fabricated with laser deposition, using different interlayer materials such as V and NiCr alloy to reduce intermetallic formation. Microstructural characterization was performed using SEM, EBSD, and EDS along the composition gradient, and mechanical properties were assessed with Vickers indentation.

9:30 AM  
Characterization of Maraging Steel to Austenitic Stainless Steel Gradient Components Fabricated with Laser Deposition: Ashley Reichardt1; John Paul Borgonia2; R. Peter Dillon2; Bryan McEnerney2; Andrew Shapiro2; Peter Hosemann1; 1University of California, Berkeley; 2Jet Propulsion Laboratory
    Laser deposition systems, when equipped with multiple powder feeders, enable layer-by-layer tailoring of composition within a single component. Using this technique, components which transition gradually between two dissimilar metals can be fabricated, thus reducing the stress concentrations and abrupt property changes typically associated with welding. Here we report on the results of additively manufacturing a functionally graded component transitioning from C300 precipitation-hardened maraging steel to 316L austenitic stainless steel in a series of 15 0.5mm-thick layers. Detailed microstructural characterization via SEM, EBSD, and EDS facilitate the mapping of grain morphology, phase, and element concentration along the composition gradient. Mechanical properties along the gradient are assessed with Vickers hardness and nanoindentation. The effects of hot isostatic pressing and age-hardening heat treatments on microstructure, mechanical properties, and observed fabrication defects such as porosity and solidification cracking are also explored.

9:50 AM  
Microstructural Control in SLM Ti-6Al-4V: Key Factors Facilitating In Situ α Martensite Decomposition: Wei Xu1; Edward Lui2; Ma Qian2; Milan Brandt2; 1Macquarie University; 2Royal Melbourne Institute of Technology University
    α martensite is usually dominant in Ti-6Al-4V additively manufactured by SLM and it is not easily achievable to transform it in situ into more desired (α+β) microstructures in the current SLM practice. Such a metastable microstructure is problematic as it leads to inadequate mechanical performances at room temperature while affecting the structural stability under loading or impacting conditions in service. Consequently, post-SLM heat treatment is often necessary. This study is motivated to optimize the SLM processing windows to achieve preferred (α+β) microstructures in situ for superior mechanical properties. We show that, through a proper selection of the SLM processing parameters, it is practical to realise significant in-situ α' martensite decomposition for precise microstructural control to produce lamellar (α+β) microstructures with a tuneable α lath width in the range of 0.18-0.75 μm. A microstructure “fingerprint” for SLM Ti-6Al-4V has thus been proposed for its future additive manufacturing with desired mechanical properties.

10:10 AM Break

10:30 AM  
Multiphase Samples Built by Additive Manufacturing: Thomas Watkins1; Amit Shyam1; Yukinori Yamamoto1; Niyanth Sridharan1; Ercan Cakmak1; Kinga Unocic1; Ryan Dehoff1; Sarma Gorti1; Srdjan Simunovic1; S. Suresh Babu2; 1ORNL; 2University of Tennessee
    In the last decade, metal additive manufacturing (AM) process has shown the potential to fabricate complex components of homogenous materials. Most of international research focuses on maturing AM to compete with traditional manufacturing processes including casting, forging and machining. None of the current efforts focuses on using the inherent site-specific building capabilities of AM. Recently, ORNL researchers have shown the proof of principle for manipulating the crystallographic texture (face-centered-cubic, FCC) in a homogeneous alloy (i.e. alloy 718). However, the generality of this scientific methodology for wide range of composition and phases has not been proven. Our overarching scientific question is the following: is it possible to disperse materials with different crystal structures (e.g. FCC, BCC and HCP) in precise geometric locations at different length scales (nm to mm) to induce tailored properties, while maintaining stability of these structures during long-term cyclic loading or thermal exposure? Current work will be shown.

10:50 AM  
Tailoring the Mechanical Properties of Ni-base Superalloys Processed by Direct Metal Laser Melting (DMLM): Thomas Etter1; Fabian Geiger1; Karsten Kunze2; 1General Electric (Switzerland) GmbH; 2ETH Zurich (ScopeM)
    Direct Metal Laser Melting (DMLM) is an additive manufacturing technology which is used to produce metallic parts from powder layers. Test specimens of the Ni-base superalloys Hastelloy X and IN738LC were built with the loading direction oriented parallel (z-specimens) and perpendicular to the building direction (xy-specimens). Specimens were investigated in the “as-built” condition and after heat treatment. The elastic anisotropy of “as-built” material is well reflected in the Young’s modulus and is different for z- and xy-specimens. It is shown that suitable scanning strategies allow tailoring the texture and thus anisotropy of mechanical properties. Otherwise, a subsequent recrystallization heat treatment significantly reduces the anisotropy and improves the creep properties of DMLM-processed IN738LC. The characterisation of microstructural and textural anisotropy was done by Electron Back Scatter Diffraction (EBSD) analysis. Predictions on Young’s modulus calculated from the measured textures for Hastelloy X compare well with the data from tensile tests.

11:10 AM  Cancelled
Characterization of Microstructure and Material Properties of Selective Laser Sintered Ni-alloy 625: Kevin Kaufmann1; Tyler Harrington1; Kenneth Vecchio1; 1University of California San Diego
    Additive manufacturing is becoming an important tool in fields including rapid prototyping and custom parts fabrication. While traditional metallurgy lacks the control of site-specific microstructure and material properties, additive layer-by-layer fabrication methods offer variability during the manufacturing process, and therefore tunability of the location-specific properties of the end product. To demonstrate this novel precision controlled processing technique, bulk samples of Ni-alloy 625 were manufactured using selective laser sintering, laser input power varied from 1.2 kW to 2 kW in 0.4 kW steps. To determine the effect of laser power on texture and microstructural development, optical microscopy and electron backscatter diffraction (EBSD) were utilized. Hardness variation throughout the samples was quantified in order to connect location specific mechanical properties to microstructure and processing parameters, and comparison to wrought 625 will be made. Overall this work serves to advance knowledge of the processing-microstructure-property relationships of laser additive manufactured Ni-based superalloys.

11:30 AM  
Influence of Processing Parameters on the Development of Microstructure and Texture in EBM Ti-6Al-4V: Todd Butler1; Kevin Chaput2; Benjamin Georgin2; Edwin Schwalbach2; 1UES, Inc. / AFRL; 2Wright-Patterson AFRL
    This work investigates the effect of build geometry on the microstructure in electron beam melted (EBM) Ti-6Al-4V. Through variation in build geometry the extremes in the “optimal” processing window of energy density could be evaluated on two regions in a single build. Microstructural characterization revealed little variation in the size of the features between regions. However, vastly different solidification textures were observed. In contrast to the <001> texture of the beta grains found in higher energy density regions, the low energy density regions exhibited a preferential alignment of <110> with the build direction, facilitating a distinctly different texture in the transformed alpha. Tensile tests conducted on specimens extracted from each region showed comparable ductility, but clear differences in yield and ultimate tensile strength. An elementary thermal process model is employed to demonstrate a rationale for the different textures.

11:50 AM  
Mapping the Decomposition of β to α in Composition and Temperature Space in Titanium Alloys: Deep Choudhuri1; Srinivas Mantri1; Chris Yannetta1; Rajarshi Banerjee1; Dipankar Banerjee2; 1University of North Texas; 2Indian Institute of Science
    The laser engineered net shape (LENS) technique has been used to prepare compositionally graded samples in the Ti-Mo system with Mo concentrations ranging from 1.5at% to about 6 at%. These permit the rapid evaluation of the effect of Mo on α morphology and distribution on direct step aging at 750C and 600C following β solution treatment. Thus α morphology and distribution have been mapped as function of Mo content and show three distinct regimes of behavior. These are colony-dominated structures that originate from grain boundary α, bundles of multiply- branched α plates, and fine plate α. These maps will permit prediction of α structures that can form in commercial titanium alloys as a function of their Mo equivalent.