Additive Manufacturing of Metals: Establishing Location-Specific Processing-Microstructure-Property Relationships: Processing-Microstructure Relationships
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.

Wednesday 8:30 AM
March 1, 2017
Room: 7B
Location: San Diego Convention Ctr

Session Chair: Judy Schneider, University of Alabama-Huntsville

8:30 AM  Invited
Accelerated Certification of Additively Manufactured Metals: Wayne King1; Andrew Anderson2; Robert Ferencz2; Neil Hodge2; Chandrika Kamath2; Saad Khairallah2; Manyalibo Matthews2; Alexander Rubenchik2; Otis Walton2; Morris Wang2; 1Lawrence Livermore National Laboratories; 2Lawrence Livermore National Laboratory
    In this presentation, we give a review of our recent progress in developing physics-based models for the metal powder bed fusion process. We first discuss a high fidelity simulation model that resolves the individual powder particles in three dimensions. We also discuss a model at the scale of the part that is used to computationally build a complete part and predict properties such as residual stress in three dimensions. The presentation highlights our effort for code validation and verification and comparison to experiments. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

9:00 AM  
Multiscale Modeling of Coupled Melt Pool Evolution and Solidification Morphology in the LENS Process: Matthew Rolchigo1; Peter Collins1; Micheal Mendoza1; Richard LeSar1; 1Iowa State University
    Evolution and solidification of the LENS melt pool are complex and interdependent processes, involving movement of fluid, heat, and solute at various length and time scales. Since as-solidified microstructures play a large role in mechanical property determination, understanding how materials and process parameters can be chosen to produce desired microstructures is critical to utilizing LENS’ full potential. We present work in which heat transport, melting, and fluid flow are modeled at the macroscale via a thermal Lattice Boltzmann model, accounting for laser absorption and Marangoni flow in the melt pool. At the microscale, solidification and solute transport are modeled using a cellular automaton model for binary alloy solidification and information passed from the macroscale. This allows linking among process parameters, melt pool conditions, and microstructure. Modeled solidification morphology as functions of both material/process parameters as well as position in the solidified melt will be examined and compared with experimental results.

9:20 AM  
Process Window Optimization for Powder Bed Additively Manufactured Molybdenum: Mustafa Megahed1; Wolfgang Ottow1; Amanda Field2; Luke Carter2; Moataz Attallah2; Michael Gorley2; Michael Porton2; 1ESI Group; 2University of Birmingham
     Molybdenum is interesting for nuclear fusion applications. It provides high temperature structural strength for in-vessel components that must withstand prolonged thermal, mechanical and irradiation loads. Powder bed additive manufacturing offers the possibility to achieve high performance concept geometries previously unattainable through traditional manufacturing routes. This paper focusses on the identification of an optimal processing window. Experiments performed using a variety of powders from different suppliers are supported by numerical models resolving the coating process, the laser powder interaction and material consolidation. Numerical models validated for nickel and titanium alloys are applied to Molybdenum to verify their applicability to refractory material analysis. Maximum component density of 97.5% was achieved using a linear energy density of 0.75 J/mm. There was little variation in results between powders tested. Directional cracking along the build direction was improved by varying build parameters.

9:40 AM  
In Situ Time and Location Resolved Measurements of Residual Stresses in Additively Manufactured 308L Stainless Steel: John Carpenter1; Donald Brown1; Bjorn Clausen1; Jason Cooley1; Adrian Losko1; Mark Bourke1; 1Los Alamos National Laboratory
    A portable additive manufacturing platform developed for in situ studies on high energy x-ray beamlines is utilized to capture both radiographic imaging and diffraction data during deposition of 308L stainless steel. Diffraction data measured at the Advanced Photon Source provides quantified phase fractions, residual stresses, and temperatures. Distinct changes in both microstructure and property evolution as a function of time and locations 100 um, 500, and 1000 um from the substrate are observed. Ex situ characterization is utilized to investigate dendrite arm spacing providing an estimate of solidification rate. Evolution of solidification rate as a function of both distance from the substrate and distance from the edge of the point deposition is shown. Implications of both ex situ and in situ results with respect to the use of additive manufacturing in repair applications are discussed.

10:00 AM Break

10:20 AM  Cancelled
Real Time Composition Control of Weld-based Additive Manufacturing: Rachel Clark1; Gerald Anzalone1; Paul Sanders1; 1Michigan Technological University
    For additive manufacturing (AM) to establish itself as a practical manufacturing method for metals, the field must develop inexpensive feedstock and processes. Rapid cooling, finer microstructure, and greater control of properties are advantages powder-based AM holds over weld-based; however the former is significantly more expensive with slower deposition rates. Previous research in weld-based AM has successfully characterized existing alloys, creating the opportunity for developing new alloys and processes to allow weld-based AM performance to compete with that of powder-based. This study explores using real time composition control of weld-based AM in order to achieve greater control of properties. Real time composition control can be achieved with a gas tungsten arc weld (GTAW) system using multiple wire dabbers, each feeding a different alloy into the weld. By taking advantage of weld-based AM’s unique processing capabilities to control microstructure and improve properties, weld-based AM can bring AM of metals to more industries.

10:40 AM  
Effect of Laser Scan Strategy on Microstructure-property Relations in Additively Manufactured Stainless Steel: Brandon McWilliams1; Jian Yu1; Andrew Gaynor1; Tomoko Sano1; Andelle Kudzal2; 1US Army Research Laboratory; 2Worchester Polytechnic Institute
    The microstructure and properties of metallic components additively manufactured (AM) using powder bed fusion processes are dependent on a large number of process variables, including laser power, hatch spacing, and orientation on the build plate as examples. The scan strategy, or path that the laser follows, is often proprietary information of the printer manufacturer, and as such, is a less studied AM design consideration. In this work the effect of the laser scanning strategy on the resulting microstructure and mechanical properties of 17-4 stainless steel is studied. Compression and tension mechanical test specimens were printed and tested using a variety of laser path scan strategies, including unidirectional, bi-directional, and concentric. The crystallographic texture and grain size of these specimens were characterized using EBSD and SEM respectively.

11:00 AM  
Microstructure Control in Additive Manufacturing of Aluminum Alloys: Hunter Martin1; Brennan Yahata2; Eric Clough2; Jacob Hundley2; Tobias Schaedler2; Tresa Pollock3; 1HRL Laboratories ; 2HRL Laboratories; 3University of California, Santa Barbara
    Additive Manufacturing of aluminum alloys has been limited to a select group of weldable Al-Si alloys, however many applications require materials with significantly higher strength. Standard high strength aluminum alloys, 2000 and 7000 series, suffer from hot tearing during solidification making them unsuitable for processing in additive manufacturing. We have developed modeling techniques to identify alloys susceptible to hot tearing and mechanisms to reduce this tendency in the unique solidification conditions during direct laser melting. By modifying material feedstock and controlling processing parameters, the hot tear susceptibility can be reduced. In addition, the microstructure and mechanical properties of additively manufacture aluminum alloys can be optimized. Through simulations the optimum solidification path can identified and parameters are tailored to control solidification of the melt pool accordingly. We will show that application of this process can be used to enable additive manufacturing of new high strength aluminum alloy systems.

11:20 AM  
Numerical and Experimental Investigation of Residual Stress Evolution in Additively Manufactured 17-4 PH Stainless Steel by Selective Laser Melting: Md Shamsujjoha1; Sean Agnew1; James Fitz-Gerald1; 1University of Virginia
    A fundamental understanding of the correlation between processing variables and mechanical deformation is essential to control the residual stress develop during selective laser melting (SLM) of 17-4 PH steel due to cyclic heating, cooling, and solid-state phase transformation. A finite element model which accounts for heat transfer, phase transformation kinetics, and elastic-plastic deformation was developed using ABAQUS. The temperature distribution in the deposited part was predicted by modeling the interaction between a moving laser heat source and the powder bed. Metallurgical transformations are taken into account using the latent heats of transformation and temperature-dependent material properties. The model works in a decoupled fashion, where the temperature field results are used in a subsequent mechanical analysis to predict the residual stresses. X-ray diffraction phase fraction and residual stress measurement was performed to validate the model. The effect of post-SLM heat treatment on the internal stresses was also investigated.

11:40 AM  
In Situ Structure and Microstructure Investigation of Heat Treatment’s Effect on AM Inconel 625: Fan Zhang1; Lyle Levine1; Andrew Allen1; Eric Lass1; Sudha Cheruvathur1; Mark Stoudt1; Maureen Williams1; Yaakov Idell1; Greta Lindwall1; Carelyn Campbell1; 1National Institute of Standards and Technology
    Additive manufacturing (AM) of metals features repetitive rapid melting and solidification in the build process, which often leads to compositional and microstructural heterogeneities. If untreated, such heterogeneities could adversely affect materials performance. Heat treatments, including stress-relieving, solutionizing, and ageing treatments, are often used to optimize the microstructures of AM materials. We have integrated synchrotron-based ultra-small angle X-ray scattering, small-angle X-ray scattering, and X-ray diffraction to simultaneously interrogate the microstructure evolution and detect emerging structural phases during various in-situ heat treatment procedures for a wide range of AM materials, such as Inconel 625, ATI 718+, and 17-4 steel. Here, we will focus on our studies of AM Inconel 625. Particularly, we will report the homogenization kinetics and the microstructural and structural evolution of precipitates and carbides. These results will be directly compared with predictions of thermo-kinetic models aimed at improving our understanding of the process-structure-properties of these alloys.