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

Monday 6:00 PM
February 27, 2017
Room: Hall B1
Location: San Diego Convention Ctr

A-1: A Study of Multiple Interfaces in Stainless Steel 316L Components Fabricated by Laser Powder Injection Deposition: Baolong Zheng1; Nancy Yang2; Joshua Yee2; Thale Smith3; James Haley1; Yizhang Zhou1; Enrique Lavernia1; Julie Schoenung1; 1University of California at Irvine; 2Sandia National Laboratories; 3University of California at Davis
    During direct fabrication of stainless steel (SS) 316L components by directed energy deposition (DED), an additive manufacturing (AM) technique, multiple interfaces were formed between subsequent tracks (inter-pass interfaces) and layers (inter-layer interfaces). Moreover, interfaces between the mesh-like cellular structures, as well as well-fused epitaxial interfaces, were also formed, due to directional solidification that follows the fast moving heat source of the laser beam. The microstructure and physical nature of these various types of interfaces can influence the mechanical behavior of laser deposited materials which was discussed earlier. In this study, laser deposition of SS316L components was carried out, with the formation of various interfaces. Furthermore, a comprehensive analysis of these multiple interfaces was performed using OM, SEM, EDS, EBSD and TEM. The objectives are to identify the physical nature of these interfaces and to provide an interpretation of their effects on the properties of AM deposited metals.

A-2: Additive Manufacturing of Ti6Al4V with GMAW: Correlation between Processing and Homogeneous Microstructural Properties: Philipp Henckell1; 1Technische Universitšt Ilmenau
    This work examines the additive manufacturing of Ti6Al4V using a wire based gas metal arc welding process. The experimental results show on the one hand the correlation of geometrical properties of the additively built structure (e.g. layer width and – height) with the processing parameters and programmed path ways. On the other hand homogeneous material properties over all layers need to be adjusted throughout a specific temperature time regime during the welding process. Therefore, hardness measurements of the additively built structures and the substrate of the same material are carried out as well as microstructural cross sections. To avoid the creation of an alpha-case oxide coating on the surface of the geometries, novel approaches of shielding additively manufactured structures from atmospheric gases are applied. The implementation and analysis of these objectives is conducted on wall and pole geometries with specified dimensions in height, width and length.

A-4: Aiming for Modeling-assisted Tailored Designs for Additive Manufacturing: Dayalan Gunasegaram1; Anthony Murphy1; Sharen Cummins1; Vincent Lemiale1; Gary Delaney1; Vu Nguyen1; Yuqing Feng1; Daniel East1; 1CSIRO
    It is well recognised that there are gaps in knowledge on the strongly intertwined process-microstructure-property-performance relationships inherent in the metallic additive manufacturing processes. Computational modelling can assist with filling in some of these gaps by increasing in-depth understanding of these relationships and highlighting cause-and-effect. Additionally, it can capture the knowledge of materials scientists and engineers and apply established physics-based rules to simulate the processes and thus predict the final outcomes. Modelling can also help optimise processes. Some even predict that future generations of additive manufacturing machines will employ ‘model-assisted feed forward algorithms’ that would leapfrog feedback control methods. In the current article the authors describe the several computational efforts sponsored by CSIRO’s Lab 22 – Australia’s Centre for Additive Innovation - aimed at modelling-assisted tailored design. The models in development, e.g. microstructure prediction (both fundamental and empirical), powder bed raking and residual stress predictions, are described in some detail.

A-5: Alloy Design for Additive Manufacturing: Preliminary Results for Al-Ce Alloys: Alex Plotkowski1; Niyanth Sridharan1; Zachary Sims2; Ryan Ott3; Ryan Dehoff2; Sudarsanam Babu1; Orlando Rios2; 1University of Tennessee - Knoxville; 2Oak Ridge National Laboratory; 3Ames National Laboratory
    Cerium is the most abundant rare earth element but is considered only a by-product of mining efforts for more critical rare-earths due to its lack of high-volume applications. Finding a large scale use for Ce would reduce the instability in extraction and stabilize the global supply of more valuable rare earths. Recent research has demonstrated the potential for Ce as the primary alloying element in a new series of Aluminum casting alloys that have shown superior fluidity and thermal stability. The goal of this work is to evaluate their viability for use in laser additive manufacturing. The microstructure of laser welds made on Al-Ce plates was evaluated and compared to the as-cast structure for two compositions. Non-equilibrium growth theory was used to rationalize the microstructural features in the weld pools. Approximate microstructural selection maps were developed to guide the choices of composition and process parameters in future additive manufacturing experiments.

A-6: Bonding Features and Microstructural Evolution in Cold Sprayed Metallic Coatings and Bulks: A New Materials Perspective: Yu Zou1; Eric Irissou2; Jean-Gabriel Legoux2; Stephen Yue3; 1Massachusetts Institute of Technology; 2National Research Council Canada (NRC); 3McGill University
    Cold spray, initially a coating technique, is being touted as a ‘near-net shape’ manufacturing technology that minimizes material waste by virtue of the high rate of deposition. During the cold spray process, metallic bulk components can be produced by spraying metal powders at high velocity, generating bonding through severe plastic deformation at temperatures well below the melting point of the powders. To fully understand the cold spray processing, we systematically study the bonding features and microstructure evolution in Cu, Ni, Al, Ti, Ti-6Al-4V samples prepared by cold spray using electron backscatter diffraction, transmission electron microscopy and nanoindentation. We show complex microstructure in these powder particles after cold spraying: nanocrystalline, nanotwins, annealing twins, gradient grains, deformation bands, dynamic/static recovery, and recrystallization. Of particular interest are grain refinement, recrystallization and particle/particle bonding mechanisms. [1]Assadi H, et al. Acta Materialia 2016 [2]Zou Y, et al. Scripta Materialia 2010 & 2009

A-7: Build Theme Modifications to Investigate Microstructural Development in Additively Manufactured 17-4PH Stainless Steel Parts: Yu Sun1; Mark Aindow1; Rainer Hebert1; 1University of Connecticut
    A combination of scanning and transmission electron microscopy studies has been used to investigate the microstructures in 17-4PH stainless steel components manufactured by selective laser melting powder-bed processing. These studies reveal a complex microstructure consisting of regions with fine and coarse ferrite grains, small amounts of retained austenite, and inclusions retained from the powder. The use of default cross-hatch scanning patterns inclined at 45˚ to the component edges complicates the analysis of the microstructure and frustrates attempts to relate these features to the melt pools from the laser tracks. To overcome these problems we have produced test samples in which the laser is scanned in a single direction parallel to the component edges, and the spacing of the tracks is increased to produce clearer separation between the melt pools. The analysis of such samples provides a clear insight into the origins of and relationships between each of the microstructural features.

A-8: Characterization of Carbide Precipitates in Nickel-Base Superalloy MAR-M247 Fabricated through Scanning Laser Epitaxy: Amrita Basak1; Suman Das1; 1Georgia Institute of Technology
    Nickel-base superalloys develop high-temperature strength primarily due to the solid-solution-strengthening and the precipitation-strengthening mechanisms typically through cobalt/chromium and aluminum/titanium, respectively. Certain other elements such as boron and zirconium are chosen for grain boundary strengthening. Such elements tend to segregate to the grain boundaries, which reduce the grain boundary energy resulting in better grain boundary cohesion and ductility. Another form of grain boundary strengthening is achieved through the addition of carbon and various carbide formers. The carbide formers drive precipitation of carbides at grain boundaries thereby reducing grain boundary sliding. Various types of carbides are possible in the microstructure of superalloys depending on the composition and processing. However, in MAR-M247 fabricated through SLE, only blocky carbides were predominantly observed. Scanning electron microscopy and energy dispersive X-ray spectroscopy investigations were carried out and the carbides were found to be tantalum-rich. This work is sponsored by the ONR through grant N00014-14-1-0658.

A-9: Characterization of Dissimilar Joint between Inconel 718 and Alloy Steel by Laser Engineered Net Shaping: Hoyeol Kim1; Zhichao Liu1; Yingge Zhou1; Weilong Cong1; Hong-Chao Zhang1; 1Texas Tech University
    Direct laser deposition is used to produce metallurgically well-bonded and higher quality coating by the advantages of reduced production time, enhanced thermal control, small heat-affected zone, and high satisfactory repair of parts. Substrate/clad interface plays a vital role in determining overall performance of the component. Most coating/hardfacing materials research focused on wear and hardness due to thin coated thickness/layer. However, in case where coating/repair area is deeper and larger, thick/multi-layer coating is highly required. Therefore there is lack of knowledge on bonding characteristics/properties of as-deposited nickel-base superalloys on dissimilar substrates. The objective of this study is to investigate fracture behavior of laser deposited Inconel 718 powders on alloy steel substrates hybrid specimens with specific emphasis on adhesion/bonding performance through tensile test. Tensile fracture surface of the hybrid specimens and tensile failure mechanisms will be discussed in detail.

A-11: Cold Gas Dynamic Spray Deposition for Additive Repair of AA7075 and AA2024 Structures: Luke Brewer1; William Story1; Sieglind Ngai1; Florian Vogel1; Benjamin White1; James Jordon1; Gregory Thompson1; 1University of Alabama
    This presentation will discuss cold gas dynamic spray deposition for the additive repair of AA7075 and AA2024 structures. Additive repair is used to replace material lost through corrosion, erosion, or wear in metallic components. High pressure cold spray deposition with both helium and nitrogen gases produced large repair volumes (6mm x 25mm x 75mm) of both alloys over a range of spray temperatures and pressures. The results show that high-quality material for both alloys can be added to the structure, but helium gas is required. Unlike plate material, cold sprayed material has microscale regions of eta (AA7075) or S (AA2024) phase, which were generated by the gas atomization process used to produce the feed stock powders. The nanoscale precipitate phases are much larger (approximately 100nm) than those found in the AA7075-T6 or AA2024-T3 plate material. Correspondingly, the as-sprayed hardness of the deposited material is considerably lower than the plate.

A-12: Additive Manufacturing of High Performance NdFeB Bonded Permanent Magnets: M. Parans Paranthaman1; Ling Li1; Orlando Rios1; Brian Post1; Vlastimil Kunc1; Cajetan Nlebedim2; 1Oak Ridge National Laboratory; 2Ames Laboratory
    The main goal of this research is to minimize the critical materials waste associated with NdFeB based permanent magnet manufacturing and reduce the overall cost. One of the ways in which we can achieve this goal is by using additive manufacturing techniques to create different shapes and complex geometries of bonded magnets. We have recently demonstrated the fabrication of near-net shape magnets with complex geometries and high energy product using 65 vol % MQP NdFeB nylon composites using Big Area Additive Manufacturing System. We will report in detail about the relationship between the processing, microstructure and property of additively printed bonded magnets. This work was supported by the Critical Materials Institute, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office.

A-14: Development of Diffusion Mobility Descriptions for Additive Manufactured Ti-6Al-4V: Greta Lindwall1; Kil-Won Moon1; Yaakov Idell1; Maureen Williams1; Fan Zhang1; Andrew Allen1; Nikolas Hrabe1; Lyle Levine1; Carelyn Campbell1; 1National Institute of Standards and Technology
    Essential for the success of additive manufacturing using electron beam melting (EBM) is control of the microstructure evolution during post-processing of the as-built part, e.g. during hot isotactic pressing (HIP). In this work, we study the role of diffusion during HIP of an EBM manufactured Ti-6Al-4V alloy. A CALPHAD-diffusion mobility description for diffusion in the α and β phase in the Ti-Al-V system is developed using information obtained from diffusion-couple experiments. The developed model is used to simulate diffusional reactions under conditions relevant to HIP post-processing. The results are discussed based on comparison with experimental investigations of the microstructure evolution using combined in situ X-ray probe (USAXS/SAXS/WAXS) measurements.

A-15: Direct Metal Writing: Controlling the Rheology through Microstructure: Wen Chen1; Luke Thornley1; Hannah Coe1; Eric Duoss1; Andrew Pascall1; Joshua Kuntz1; Christopher Spadaccini1; 1Lawrence Livermore National Laboratory
    Additive manufacturing of metals is a challenge. Most metal additive manufacturing approaches are based on powder-bed melting techniques such as laser selective melting or electron beam melting, which often yield uncontrolled microstructures containing remarkable defects (e.g., pores or microcracks) and residual stresses. Here, we introduce a proof-of-concept prototype of three dimensional metal freeform fabrication process by direct writing of metallic alloys in the semi-solid regime. This is achieved through controlling the particular microstructure and the rheological behavior of semi-solid alloy slurries which demonstrate a well suited viscosity and shear thinning properties to retain shape upon solidification. The versatile microstructural manipulation within this method yields a flexible manufacturing route to fabricating three dimensional metal parts with full density and complex geometries that is unachievable by conventional metal additive manufacturing or processing methods such as casting or forming. Prepared by LLNL under Contract DE-AC52-07NA27344.

A-16: Effect of Build Orientation on the Microstructure and Mechanical Properties of Selective Laser Melted Ti-6Al-4V Alloys: Patrick Hartunian1; Mohsen Eshraghi1; 1California State University, Los Angeles
    Ti-6Al-4V alloy has a high strength-to-weight ratio, high corrosion resistance, along with good fatigue and creep properties. Developments and advances in additive manufacturing have created new horizons for enhanced processing and manufacturing of Ti-6Al-4V alloy. A major challenge of the additive manufacturing techniques is the inability to achieve identical microstructure and mechanical properties in different build orientations. In this work, the microstructure and mechanical properties of additively manufactured samples were studied and compared with traditionally processed samples. Rectangular samples were printed using the Renishaw’s AM250 selective laser melting system. The samples were fabricated in three perpendicular orientations. Tensile test specimens were machined from the printed samples and the fracture toughness specimens were tested as fabricated. Effect of build orientation on the microstructure and mechanical properties of selective laser melted Ti-6Al-4V samples was studied.

A-18: Effect of Microstructure on the High-temperature Oxidation Behavior of Inconel 718 Manufactured via Electron Beam Melting: Alfred Okello1; Michael Kirka1; Ryan Dehoff1; 1Oak Ridge National Laboratory
    The nickel-iron-base superalloy Inconel 718 is the most widely used superalloy in the aerospace community due its high-temperature creep strength, weldability, corrosion and oxidation resistance. Fabrication via additive manufacturing with electron beam melting (EBM) uses an electron beam as a heat source to melt successive powder layers, and provides an alternative for fabrication of complex near-net shape Inconel 718 parts that are impossible through traditional forging and casting processes. Another advantage of EBM is the possibility to control microstructure to produce columnar or equiax grains within the material. The current study presents an evaluation of the oxidation behavior of EBM 718 with different microstructures (equiax/columnar grains) in comparison to the traditionally wrought alloy. The morphology and extent of oxidation will be investigated by optical and scanning electron microscopy.

A-19: Effect of Print Parameters on Microstructure of EBM Printed Ti-6Al-4V: Colleen Hilla1; Sean Yoder2; Peeyush Nandwana2; Ryan Dehoff2; Kinga Unocic2; 1University of Pittsburgh ; 2Oak Ridge National Laboratory
    As Additive Manufacturing (AM) rapidly transitions from small laboratory production to real world applications, the correlation between microstructure, mechanical properties and processing parameters needs to be fully understood. In Electron Beam Melting (EBM) a number of processing parameters can be adjusted with each having an effect on the microstructure of the final component. In addition, layer preheat and print location also impact sample microstructure causing multidirectional microstructure gradients throughout the sample. In this study Ti-6Al-4V powder was used to build complex shape component and the goal is to correlate the effect of processing parameters, feature size of the component, and print location in an EBM Ti-6Al-4V complex component, on the microstructural evolution. An EBM printed workpiece will be sectioned into metallographic samples for detailed microstructural analysis using optical microscopy, scanning electron microscopy in conjunction with energy dispersive x-ray spectroscopy, and electron backscatter diffraction analysis.

A-20: Effects of Recycled Powder on Build Integrity in Metal Based Additive Manufacturing: Katherine Terrassa1; Nancy Yang2; Julie Schoenung1; 1University of California, Irvine; 2Sandia National Laboratories
    Metal based additive manufacturing has struggled to become a widely utilized process partially due to the need to improve the economic impact of these techniques. For direct laser deposition, 90% of feedstock powder is unused. The convention is often for this powder to be discarded to prevent negative effects on build quality if reused due to the possible morphological and microstructural changes in the powder resulting from interactions with the laser. However, recent studies have shown that the morphology of the powder can be maintained for multiple deposition cycles if properly processed. In this study, 316L stainless steel powder is used as feedstock in a Laser Engineered Net Shaping (LENS) machine. The effects of the recycled powder, including the particle morphology, agglomeration, composition and microstructure, on the quality of the build are investigated through scanning electron microscopy, particle size analysis, and mechanical testing.

A-21: Electron Microscopy Study of Non-metallic Inclusions in Additively Manufactured 17-4PH Stainless Steel Parts: Yu Sun1; Mark Aindow1; Rainer Hebert1; 1University of Connecticut
    Traditional steel processing inevitably introduces non-metallic inclusions in microstructures with oftentimes detrimental effects on mechanical properties. Non-metallic inclusions are also present in 17-4 PH virgin powder that is used for additive manufacturing and are furthermore observed in parts that were manufactured with a 3D Systems ProX-300 powder bed machine. In this study, advanced analytical electron microscopies (TEM, SEM) are applied to characterize the morphology, chemistry and size of non-metallic inclusions in 17-4 PH virgin powders and parts. Inclusion particles vary in size from tens of nanometers to several micrometers in diameter. The similarity in size and chemistry between the inclusions in the starting powders and the finished parts suggests that the inclusions in the starting powder are maintained in the final parts. The apparent survival of inclusions during the additive manufacturing process offers opportunities to control additively manufactured part properties with initial powder control.

A-22: Fatigue and Fracture in Additive Manufacturing Metals: Findings from a Recent NIST/ASTM Workshop: Nikolas Hrabe1; Steve Daniewicz2; Nima Shamsaei2; Nicholas Barbosa1; 1National Institute of Standards and Technology; 2Mississippi State University
    There is a large industrial motivation to expand use of additively manufactured metals to fatigue and fracture critical applications, but this is made difficult by a general lack of understanding of fatigue and fracture behavior of these materials. Findings from a recent workshop (NIST/ASTM “Workshop on Mechanical Behavior of Additive Manufactured Components”, ASTM Committee Week May 4-5 2016, San Antonio, TX) will be presented to provide clarification on the current state of understanding as well as specify current industrial needs and priorities (including preferences for certain fatigue and fracture properties, material systems, and metal additive manufacturing platforms). These findings will help the research community focus and provide motivation for its efforts in this area.

A-23: Finite Element Analysis of Hybrid Additive Manufacturing to Print Location Specific Mechanical Properties by Sequential Laser Shock Peening: Michael Sealy1; Guru Madireddy1; Chao Li2; Yuebin Guo2; 1University of Nebraska-Lincoln; 2The University of Alabama
    Hybrid additive manufacturing is the combination of two or more manufacturing processes or materials that synergistically affect the quality and performance of a printed part. In this study, a hybrid-AM approach entails coupling laser shock peening (LSP) and selective laser melting (SLM) for the purpose of printing location specific mechanical properties that could benefit corrosion and fatigue performance. LSP is a surface treatment to impart residual stresses and increase microhardness. When coupled with SLM, the heat from the laser has the potential to relax any favorable compressive residual stresses from LSP. Thus, the objective of this study was to better understand the relationship between a hybrid-AM process and the resulting mechanical properties. Sequential LSP was coupled with SLM in a 2D finite element simulation in Abaqus to quantify the resulting residual stress fields. The effects of multiple peening was investigated.

A-24: Grain Growth and Heat Flux Direction during Selective Laser Melting of CoCrMo Alloy: Zhan Chen1; M.A.L. Phan1; K. Darvish1; 1Auckland University of Technology
    The propensity of forming microcracks during selective laser melting (SLM) and mechanical properties of SLM parts closely link to how grains grow during SLM solidification. Epitaxial and columnar (cellular or dendritic) growth are the prevalent forms of solidification within a melt track during SLM, particularly during SLM of CoCrMo alloy which has been extensively studied. However, depending on scanning strategy and thus variation of heat flux direction from one layer to another, morphology of grains may vary. In this work, SEM imaging and EBSD analysis of SLM CoCrMo samples make using zigzag hatching strategy have been conducted. Long columnar grains across many tracks with each grain consisting a large number of cells, as often observed, and grains with growth directions of cells and thus the grains changed at track boundaries are shown. These growth manners related to heat flux directions, influenced by the scanning strategy, will be explained.

A-25: High-strength, Corrosion-resistant, Weldable Aluminum Powders for Additive Manufacturing: Nhon Vo1; Amirreza Sanaty Zadeh1; Davaadorj Bayansan1; Evander Rumos1; David Seidman1; David Dunand1; 1NanoAl LLC
    In contrast to the rapid growth of additive manufacturing of metals, including aluminum alloys, there is currently a limited number of commercial aluminum powders that are suitable for powder-bed 3D-printing. The mechanical strength of these aluminum powders is, however, relatively low. Aluminum alloys containing magnesium and high concentrations of scandium are promising in terms of excellent mechanical strength, corrosion resistance and 3D-printing capability. These alloys are, however, expensive due the high cost of scandium. We present the development of new, economical, high-strength and corrosion resistant aluminum powders. The powders do not contain expensive elements, thereby having a low material cost. The strengthening mechanisms are a combination of solid-solution hardening and a high number density of primary micro-precipitates and secondary nano-precipitates. The powders have good weldability, thus they are suitable for powder-bed 3D-printing. Powder fabrication methods and additive manufacturing processes for the developed aluminum powders are discussed.

A-27: In Operando Synchrotron X-ray Imaging of Selective Laser Melting: Chu Lun Alex Leung1; Robert Atwood2; Michael Towrie3; Philip Withers1; Peter Lee1; 1University of Manchester; 2Diamond Light Source Ltd; 3Science Technology Facilities Council
    Synchrotron X-ray imaging was used to observe and quantify the melting and solidification processes during laser additive manufacturing (AM), termed in operando imaging. In this study a unique Laser Additive Manufacturing Process Replicator (LAMPR) was designed, implemented, and coupled into the Joint Engineering, Environmental, and Processing (JEEP) beamline at Diamond Light Source. The LAMPR was used to perform real-time observations of melt pool evolution beneath the powder surface during selective laser melting (SLM) of SS316 powder. The results of this study provide new insights in particle and melt pool dynamics, helping both inform and validate numerical models of melt pool evolution during SLM.

A-28: Incorporating Complex Thermal Histories in Grain Microstructure Simulations of Additively Manufactured 316L SS: Kyle Johnson1; Theron Rodgers1; Joseph Bishop1; 1Sandia National Laboratories
    Predicting microstructure evolution due to the rapid solidification and complex thermal histories of additive manufacturing (AM) is key to understanding the resulting process-structure-property relationships. To meet this objective, this research employed numerical heat transfer modeling combined with kinetic Monte Carlo (KMC) simulations. Previously, the KMC technique has been utilized to predict grain morphology using linear temperature gradients without time evolution. To further refine microstructure predictions using this method, spatial temperature histories were generated by simulating the production of a 316L stainless steel tube via powder bed technique. The temperature histories were then used in KMC simulations to model microstructure evolution of grain morphology. These results provide a novel methodology linking physically based thermal simulations to microstructure. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.

A-29: Laser Additive Manufacturing of Nanoparticles Reinforced Aluminum: Ting Chiang Lin1; Jingzhou Zhao1; Chezheng Cao1; Xiaochun Li1; 1University of California Los Angeles
    Metal matrix nanocomposite (MMNCs) have emerged as an important class of metallic material exhibiting excellent mechanical, physical, and chemical properties. Lightweight MMNCs, such as nanoparticle reinforced aluminum, will be of significance to improve energy efficiency for numerous applications. In this work, the additive manufacturing of TiC nanoparticles reinforced aluminum was studied via Selective Laser Melting (SLM). The novel Al/TiC nanocomposite powders used for SLM were prepared through a nanoparticle self-assembly mechanism in molten salts. The experimental study revealed the effects of TiC nanoparticles and laser processing parameters on microstructure characteristics (distribution of nanoparticles, grain size, and phase morphology of the matrix) and material properties (hardness, surface topography, and geometrical accuracy) of the Al/TiC nanocomposites.

A-30: Machine Learning Approaches to Optimize Additive Manufacturing Parameters for SLM of Inconel 718: Branden Kappes1; Henry Geerlings1; Senthamilaruvi Moorthy1; Andrew Petersen1; Douglas Van Bossuyt1; Aaron Stebner1; 1Colorado School of Mines
    We have tested samples from five SLM build plates, each with 625 cylindrical Inconel 718 samples, and have used these 3125 samples to develop high throughput characterization and analysis procedures. These data serve as the basis for development of machine learning (ML) algorithms, from principal component analysis to ensemble classification and neural networks, that focus on two-way modeling of the process-property and process-structure relationships. Our results show that laser power, speed, spot size, pass overlap, even sample orientation and position on the build plate significantly effect microstructure, particularly porosity, which in turn, has a pronounced effect on the mechanical performance of the sample. We will present on the data collection, processing, validation and distribution framework; on ML performance, accuracy and validation procedures; and conclude with a brief discussion on the extension of this model to other data input streams and materials systems.

A-31: Microstructure vs. Mechanical Properties for Different Al Alloys Deposited by Cold Spray Process: Reza Rokni1; Steve Nutt1; 1University of Southern California
    In cold spray process, coatings are produced by depositing powder particles at high velocity onto a substrate, creating bonding with the substrate at temperatures below the melting point of the powder particles. our investigations underscored the retaining of feedstock microstructures into deposits. However, metastable microstructures including high dislocation density, ultra fine grained, nano, and pancaked grained structures were observed through detailed microstructure characterization of different regions in the deposits. It was also found that those metastable microstructures remarkably affect the local deposition properties such as nanohardness. The evolution mechanisms of metastable microstructure in different cold sprayed aluminum depositions were examined via different microscopy techniques. Also, the microstructural stability of these metastable features were investigated by in-situ heating to a fully annealed state via a hot-stage transmission electron microscope.

A-32: Modeling the Effects of Texture on Process-structure-property Evolution in Additively Manufactured Metals: Judith Brown1; Joseph Bishop1; Theron Rodgers1; 1Sandia National Laboratories
    A process-structure-property modeling approach was developed to study texture evolution in additively manufactured structures and the resulting effects on mechanical properties. Texture evolution was modeled as a function of thermal gradients and solidification processes in the melt pool, and the macroscale mechanical properties were determined through computational homogenization of the resulting microstructures. The approach is used to investigate the effects of processing parameters such as laser power and scan speed on both microscale and macroscale behavior in FCC metals. The predictions indicate the resulting mechanical properties can have various degrees of anisotropy related to the solidification textures present.

A-33: Phase Field Modeling of Solidification Microstructure during Laser Sintering of Inconel 625: Supriyo Ghosh1; Jonathan Guyer1; 1National Institute of Standards and Technology
    Additive manufacturing via direct metal laser sintering (DMLS) is a relatively recent technology in which metallic parts are produced in a layer by layer fashion by melting (or sintering) and fusing the metallic powders. The evolution of microstructure in this process depends primarily on the melt-pool characteristics as well as the processing conditions. To study this, we use a phase field model for directional solidification of a dilute binary alloy approximating Inconel 625. The resulting morphologies vary from columnar to dendritic to equiaxed depending on temperature gradient and the laser scan speed. Moreover, events like solute trapping and spacing selection may reveal new insights in this rapid solidification regime. Finally, results are compared with existing findings.

A-34: Physics Based Modeling of Laser Powder Bed Fusion Process Applied to Inconel 718: Ranadip Acharya1; John Sharon1; Alexander Staroselsky1; Tahany El-Wardany1; Vijay Jagdale1; Gajawalli Srinivasan1; William Tredway1; 1United Technologies Research Center
    In the powder bed fusion process, material is deposited layer-by-layer by utilizing a heat source to melt the powder material of interest on a substrate or previously deposited layer. Melting, re-melting and solidification processes introduce thermal gradients in the material which give rise to residual stresses and distortions. The melt pool analysis accounts for moving heat source, melt convection and Marangoni effect in order to accurately estimate its shape and temperature distribution. The results obtained from melt pool analysis were further used for as-deposited microstructure prediction. Using fully coupled phase-field equations, the development and growth of dendritic structures has been analyzed. Models are validated using single track laser powder bed deposition experiments for Inconel718 feedstock. Predicted melt pool shapes, microstructures specific for different processing parameters have been compared against experimental melt pool dimensions and dendritic structure. Finally, the developed modeling framework allows predicting the microstructure-driven mechanical properties of additively-manufactured parts.

A-35: Prediction of the Balling Defect by a Mesoscale Transient Model Combining Heat Transfer and Fluid Flow: Yi Li1; Yousub Lee1; Ji-Cheng Zhao1; Wei Zhang1; 1The Ohio State University
    Laser-powder bed fusion (L-PBF) additive manufacturing involves a complex combination of physical phenomena, and understanding of which will help predict the formation of defects and facilitate quality control. Existing mesoscale heat transfer and fluid flow models were utilized to simulate the temperature distribution, fluid flow and surface profile of the molten pool in the powder particle level during laser fusion. The effect of processing conditions on weld pool geometry and defect formation was also investigated experimentally by varying the laser power and scan speed on multiple linear single tracks that were fused using AISI 316L powder and L-PBF. High-speed infrared thermography was incorporated co-axially with the laser beam to track the local laser beam temperature profile. After deposition, optical profilometer was used to examine the balling defect. Both transverse and longitudinal weld pool geometries were observed and compared with the simulation predictions.

A-36: Progress toward Predicting Rapidly Solidified Microstructures of Metallic Alloys: John Roehling1; Aurelien Perron1; Jean-Luc Fattebert1; Gabe Guss1; Manyalibo Matthews1; Patrice Turchi1; Joseph McKeown1; 1Lawrence Livermore National Laboratory
    Complete prediction of rapidly solidified microstructures requires full knowledge of the thermal, solutal, and free-energy fields of the solidifying material. Phase-field simulations have the ability to properly track these fields and therefore predict solidification microstructures. However, to achieve suitably predictive models, the results must be informed by experimental data. This work highlights recent progress toward validating predictive (phase-field) modeling capabilities with in situ and ex situ experimental observations of rapidly solidified alloys, using the dynamic transmission electron microscope (DTEM) at LLNL. The in situ DTEM measurements allow two-dimensional experiments to be compared directly with phase-field models in order to better understand the non-equilibrium structures produced during rapid solidification. This work was performed under the auspices of the U.S. Department of Energy (DOE) by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Work was funded by the Laboratory Directed Research and Development Program at LLNL under project tracking code 15-ERD-006.

A-37: Role of Grain Orientation and Prior Beta Grain Structures on the Anisotropic Behavior of Additively Manufactured Ti-6Al-4V Components: Jay Keist1; Daudi Waryoba2; Todd Palmer1; 1Applied Research Laboratory Penn State; 2Penn State DuBois
    As-deposited additively manufactured (AM) Ti-6Al-4V components fabricated by laser based directed energy deposition (DED) exhibited both location and orientation dependent mechanical properties. In addition, the thermal expansion behavior was also dependent on orientation. Secondary processing by hot isostatic pressing (HIP) reduced the location dependencies but the orientation dependencies remained. This anisotropic behavior for both the mechanical and thermal expansion properties appeared to be related to the prior-beta grain morphology. The prior-beta grain morphology depended on such considerations as geometry, size of the component, and the dwell time between the deposition of individual layers. Electron backscattered diffraction (EBSD) analysis and other characterization tools were used to connect the prior-beta grain boundary region morphologies with the resulting material properties of AM Ti-6Al-4V components. By connecting the structure of these prior beta grain boundary regions with the role of different processing conditions, the origins of anisotropy in these AM structures can be determined.

A-38: Strengthening of 316L Stainless Steel by the Addition of Nanoparticles: Bandar AlMangour1; Dariusz Grzesiak2; Jenn-Ming Yang1; 1University of California Los Angeles; 2West Pomeranian University of Technology
     The 316L stainless steel alloys are known for their excellent resistance to corrosion and suitably high ductility. However, even though 316L stainless steel is a desirable material, it exhibits poor mechanical properties at high temperatures, undergoes thermal shock, and has limited wear resistance. Strategies to solve these issues have entailed incorporating secondary phases such as ceramic particulates with sizes in the nano range at the matrix grain boundaries. One way to produce nanostructured materials is by "mechanical alloying," which is a nonequilibrium, low-temperature, and solid-state powder processing technique. In this work, we introduced selective laser melting to fabricate 316L stainless steel nanocomposites. The microstructure-properties relationship were established, so that nanocomposite parts with a novel nanoscale reinforcement architecture and improved performance can be fabricated successfully. We believe that the current research work as it concentrate in alternative fabrication route, it would significantly increase their widespread use in the future.

A-39: Sub-surface Material Interactions in Laser Polishing Electron Beam Additive Manufactured Ti6Al4V Components: Yingtao Tian1; Wojciech Gora2; Aldara Pan Cabo2; Lakshmi Parimi3; Duncan Hand2; Philip Prangnell1; 1The University of Manchester; 2Heriot-Watt University; 3GKN Aerospace
    Laser polishing (LP) is an emerging technique with potential for smoothing the rough fatigue initiation prone surface of additive manufactured (AM) components. It uses a laser to re-melt a thin surface layer and smooth the surface due to surface tension in the melt pool. However, re-melting and solidifying the surface layer can significantly modify the subsurface material. This study has used an EBM Ti6Al4V component as an example to address these key issues and evaluate the capability of this technique for improving the surface quality of AM parts. Experiments have shown that the surface roughness can be reduced by over 85%, but the re-melted layer undergoes a change in texture and a martensitic transformation which results in a small increase in hardness. In addition, a significant level of surface residual stresses was generated, but these can be relaxed to virtually zero by standard stress relief heat treatment.

A-40: Sulfuric Acid Corrosion to Simulate Microbial Influenced Corrosion on Stainless Steel 420: Jacob Miller1; Holly Martin1; 1Youngstown State University
    The continued improvement of additive manufacturing is progressively eliminating the geometric limitations of traditional subtractive processes. Because parts are built up in thin layers, such as in processes like Selective Laser Sintering, complex parts can be manufactured easily. However, this manufacturing method causes the parts to be more porous than their traditional counterparts. The effect of this difference has not been researched thoroughly, but may have a significant impact on the properties of the parts. For example, the porous additive manufactured parts could easily collect micro-organisms that produce sulfuric acid as byproducts of their metabolic processes. Uninhibited microbial growth within the pores could produce enough sulfuric acid to degrade the parts through hydrogen embrittlement. This research contrasts the tensile strength and corrosion behavior of 420 stainless steel between traditional and additive manufactured parts based on exposure time to a 0.75 molar sulfuric acid solution, which mimics microbial metabolic byproducts.

A-41: Synchrotron X-ray Characterization of Powder-bed Fusion Laser Melt Traces on Solid Nickel-based Super Alloy Plates: Thien Phan1; Lyle Levine1; Mark Stoudt1; Jarred Heigel1; 1National Institute of Standards and Technology
    Additive manufacturing using powder-bed fusion laser sintering allows fabrication of complex metal parts. However, the microstructures and residual stresses of the as-built parts depend on numerous processing parameters and powder variables. Therefore, it is crucial to understand the influences of the processing parameters, starting with the simplest case: laser melt traces on bare alloy plates. Here, we investigate the geometries, 3D microstructures and local (sub-micrometer length scale) residual stresses of single and multiple laser melt traces for two combinations of laser power level and scan speed on bare IN625 plates. Stresses are measured using synchrotron microbeam X-ray diffraction. Optical methods and SEM are used to study the melt pool cross sections, primary and secondary dendritic arm spacings, and compositional segregation. These single melt trace results serve as a foundation for correlating microstructures and residual stresses to processing parameters and provide essential validation tests for FEA simulations.

A-43: Utilization of In Situ Process Monitoring for Determining Consistency in Additive Manufacturing and Flaw Detection: Jake Raplee1; Suresh Babu1; Michael Kirka2; Ralph Dinwiddie2; Ryan Dehoff2; 1University of Tennessee Knoxville; 2Oak Ridge National Laboratory
    In most cases Additive Manufacturing provides better handling of complex geometries and greater design freedom over traditional manufacturing processes. However, little is known about what takes place during the build process in terms of material structure and consistency of the finished products. In order to gain a better understanding of what is taking place during additive manufacturing processes some research has started using in-situ process monitoring techniques with both optical and thermal imaging equipment to understand flaws and analyze the process in real time. The goal of this work is to determine how these technologies can be used to gain a better understanding within the additive build process as well as understand what factors outside of process parameters may have an impact on the additive manufacturing process.