Additive Manufacturing: Building the Pathway towards Process and Material Qualification: Poster Session
Sponsored by: TMS Extraction and Processing Division, TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Mechanical Behavior of Materials Committee, TMS: Powder Materials Committee, TMS: Process Technology and Modeling Committee, TMS: Additive Manufacturing Bridge Committee
Program Organizers: John Carpenter, Los Alamos National Laboratory; David Bourell, University of Texas - Austin; Allison Beese, Pennsylvania State University; James Sears, GE Global Research Center; Reginald Hamilton, Pennsylvania State University; Rajiv Mishra, University of North Texas; Edward Herderick, GE Corporate
Monday 6:00 PM
February 27, 2017
Room: Hall B1
Location: San Diego Convention Ctr
A-44: A Partial Solution to Modeling the Anisotropic Material Properties of Fused Deposition Modeling ABS: Part 2 of 2: Ross Fischer1; Keenan Jewkes1; Scott Kessler1; 1Colorado Mesa University
This study utilized an artificial neural network (ANN) to develop a partial solution to modeling the anisotropic behavior of fused deposition modeling (FDM) manufactured parts in two-dimensions. Test specimens were printed with rectilinear patterns at variable raster orientations and their tensile properties were determined through tensile testing. The tensile data for the [0/90], [30/-60], and [45/-45] raster orientations where used to train the ANN – where raster orientation was ANN input and tensile properties were output. During the validation and testing phase tensile data for a [15/-75] orientation were predicted by the ANN. The ANN can accurately predict tensile properties in the XY-plane independent of load presence or configuration. If this ANN material model were incorporated within finite element analysis software – which past literature has shown to be reasonable – modeling the anisotropic behavior of FDM manufactured parts would be well within reach.
A-45: A Simulation Framework for Quantifying Uncertainty in the Mechanical Performance of Additively Manufactured Parts: Kai Wing Kelvin Leung1; Azadeh Keshtgar1; Nagaraja Iyyer1; 1Technical Data Analysis Inc.
Additive manufacturing (AM) technology offers rapid prototyping and large design freedom, however, it remains challenging to certify AM parts as final quality varies due to process variations. Therefore, we propose a simulation framework to quantify uncertainty in the mechanical performance during Selective Laser Melting process due to variations in laser characteristics and ambient temperature. The proposed framework consists of a thermo-mechanical finite element model to compute thermal history and residual stresses, a microstructure evolution model to predict grain size distribution and microstructure composition from the thermal history, and an analytic approach to estimate mechanical performance. A probabilistic prediction approach is proposed to quantify the uncertainties and reduce the computational cost. The proposed method characterizes the propagation of uncertainties due to the variabilities in laser power, laser beam width, scan speed and ambient temperature into the mechanical performance metrics using the developed simulation tool.
A-46: Composite Powder Consolidation Using Selective Laser Melting: Input Energy/Porosity Morphology/Balling Effect Relation: Hala Salem1; Hanadi Salem1; Moataz Attallah2; 1The American University in Cairo; 2University of Birmingham
In this study Al2O3/AlSi10Mg composite was processed via selective laser melting. The influence of different process parameters namely, laser power, scan speed and hatch spacing was investigated to determine their effect on the physical and mechanical properties of the consolidated powders. Input energy and balling effect, had a major influence the developed pore morphology. Poor consolidation associated with poor diffusion occurred at the low input energy. Intermediate input energy resulted in the formation of continuous porosity along the building direction separated by consolidated zones of equal width and associated with uniform balling effect. High input energy developed distorted porosity with nonuniform distribution associated with irregular coarse balling effect. The formed continuous porosity is attributed to the segregation and migration of alumina particles to the spacing between the deposited successive powder layers followed by their selective melting forming oxide films that acts as a barrier to the complete solidification.
A-47: Current Process Limitations of Synthetic Rock Fabrication Using Additive Manufacturing: Kevin Hodder1; John Nychka1; Rick Chalaturnyk1; 1University of Alberta
There is an economical and scientific drive for the fabrication of synthetic rock cores for study in the geological sector. Through additive manufacturing, sandstone can be fabricated using a powder bed system, where layers of sand are printed upon with a binder jet print head. With additive manufacturing, extrinsic defects caused by coring can be avoided and internal defects, such as voids and fractures, can be placed with precision during fabrication. However, although the dimensions and features of the synthetic rock can be controlled, the unconfined compressive strength of the samples is less than natural sandstone due to the polymer binder used during fabrication. The following paper will outline the current printing procedure, capabilities and limitations of the printing process.
A-48: Design and Additive Manufacturing of a Scale Model Heat Exchanger for Geothermal Applications: Adrian Sabau1; James Klett1; Derek Byrd1; Keith Carver1; Frederick List III1; Yarom Polsky1; 1Oak Ridge National Laboratory
Novel geometries for the flow path and overall architectures of the boiler/evaporator for geothermal applications need to be investigated in order to develop compact and efficient heat exchangers for geothermal power plants. Additive manufacturing, in which intricate near net shape parts are created by successive addition of metal under laser and/or electron beams to form near net shape parts, offers the opportunity of creating breakthrough designs. A new evaporator architecture was designed to allow better fluid transport and greater heat exchange between the brine and refrigerant. Computational Fluid Dynamics simulations were used to assess the performance of the newly designed evaporator. In order to test a new proposed evaporator design, a scale-down prototype was fabricated using a laser-based additive manufacturing process. Several challenges posed by the laser-powder-bed fabrication were presented and solutions were discussed. Finally, a modified geometry configuration that was successfully fabricated using additive manufacturing is presented.
A-49: Qualification of Products Manufactured by Additive Manufacturing as per DNVGL-SE-0160: Harsharn Tathgar1; Hanne Hjerpetjonn1; Sastry Kandukuri1; 1DNVGL – Section of Materials Technology
Additive manufacturing (AM) is not fully embraced for structurally critical parts in aerospace, maritime, and oil and gas; as the processes and material qualification programs from credible classification and certification societies are not fully developed to our knowledge. DNVGL is one of the world’s largest classification and certification society, has developed a systematic approach with basis in the technology qualification process described in DNVGL-RP-A203 to document that a technology is qualified according to DNVGL-SE-0160.When an adequate set of acceptance criteria and limits does not exist for a technology, then technology qualification with requirements validation enables the delivery of equipment, devices and facilities that are in demand, as well as the operation of these in the manner that is needed. Technology qualification entails developing and substantiating the acceptance criteria for products and the limits to operations which will assure the reliable, defined functionality. This poster will describe steps required in the technology qualification process.
A-50: Evaluation of Graphene Reinforced Aluminum Prepared by Ball Milling and Selective Laser Melting: Yachao Wang1; Jing Shi1; Shiqiang Lu2; 1University of Cincinnati; 2Nanchang Hangkong University
Graphene possesses many outstanding properties, such as high strengths, light weight, making it an ideal reinforcement for metal matrix composite (MMCs). Meanwhile, fabricating MMCs through laser assisted additive manufacturing (LAAM) has attracted much attention in recent years due to the advantages of low waste, high precision, short production lead time, and high flexibility. In this study, graphene reinforced aluminum is fabricated using selective laser melting. Composite powder is prepared using high-energy ball milling and the effect of ball milling duration on graphene quality is investigated. Moreover, room temperature tensile tests are conducted to evaluate the tensile properties. In order to understand the reinforcing mechanism, scanning electron microscopy (SEM) observations are conducted to investigate the microstructure and fracture surface of obtain composite. It is found that fabrication of GNPs reinforced aluminum using SLM is a viable approach. The obtained composite possesses dense microstructure and significantly enhanced tensile strength.
A-51: Experimental Technique for Extracting Local Mechanical Behavior from AM Components with Spatially Varying Mechanical Properties for Correlation with FEA Modeling: Denver Seely1; David Francis1; 1Mississippi State University/Center for Advanced Vehicular Systems
Predictively modeling the constitutive behavior of as deposited metal AM parts presents a challenge. Complex thermal histories can produce heterogeneous microstructures with varied mechanical behavior within a single part having a single chemical composition. In addition, by making use of the AM capability of varying composition locally, functional grading of mechanical properties can be intentionally introduced. Computational models of heterogeneous material distribution rely on accurate material models and valid assumptions about interactions between materials. Obtaining accurate local mechanical behavior is important for calibrating microstructurally sensitive constitutive models. This presents a challenge for calibration experiments with regard to specimen design. Validating the assumptions of computational models that make use of functionally graded properties also require accurate local mechanical measurements. We show the application of a digital image correlation technique to extract local mechanical behavior for model calibration, then show the application to a functionally graded experiment compared with an FEA model.
A-53: Feasibility Study of Making ã-TiAl Parts with Electron Beam Melting: Pathway towards Additively Manufacturing Complex Engine Components: Ercan Cakmak1; Indrani Sen2; Peeyush Nandwana1; Thomas Watkins1; Ryan Dehoff1; Roger England3; Allen Haynes1; 1Oak Ridge National Laboratory; 2India Institute of Technology Kharagpur; 3Cummins Inc.
Titanium aluminide alloys based on the γ-TiAl phase have been of great interest owing to their high specific strength, good strength retention and good corrosion and oxidation resistance at high temperatures. However, their brittle nature makes them hard to manufacture and machine using conventional techniques. Additive manufacturing is a promising alternative for the manufacture of complex geometries with its near net shape manufacturing capability. In this feasibility work, TiAl preforms have been manufactured using the electron beam melting technique. Mechanical testing was performed both at room and high temperature. Characterization experiments were performed to assess the constituent phases, residual stresses, microstructures and grain orientations. Effect of process conditions on the resultant microstructures and microstructure-mechanical property relations are discussed.
A-54: In Situ Neutron Diffraction Measurements on Additively Manufactured Stainless Steel: Bjørn Clausen1; Donald Brown1; John Carpenter1; Kester Clarke2; Amy Clarke2; John Bernardin1; Dusan Spernjak1; James Thompson1; 1Los Alamos National Laboratory; 2Colorado School of Mines
In the pursuit of achieving process based qualification of additively manufactured parts, the relationships between processing, structure, properties and performance (PSPP) of the final objects must be characterized and understood in order to develop predictive modeling tools. We will demonstrate how applying in-situ neutron diffraction measurements during processing (heat treatment and mechanical loading) can provide detailed experimental information about all PSPP steps. The in-situ measurements were performed using the SMARTS neutron diffractometer at Los Alamos National Laboratory (LANL) on material made from GP-1 (17-4) stainless steel powder (EOS) using the powder bed technique at LANL. The diffraction data provides direct information about the development of microstructure, phase, internal stress and texture during processing, as well as residual stresses in parts after manufacture. The experimental data will directly feed into microstructure aware models for the AM materials being developed at LANL.
A-55: In Situ Nondestructive Evaluation for Achieving Closed Loop Feedback Control of Ultrasonic Additive Manufacturing: Venkata Karthik Nadimpalli1; Li Yang1; Peter Nagy2; 1University of Louisville; 2University of Cincinnati
Ultrasonic Additive Manufacturing (UAM) is a layer by layer solid state fusion process. The power drawn during manufacturing has been theorized to be an indicator of bond quality which can be changed by controlling the vibration amplitude. An in-situ monitoring setup has been built that houses a 5 MHz ultrasonic transducer embedded in the base plate on which UAM processing occurs. A range of vibration amplitudes have been used to build components of varying degrees of qualities. An interfacial spring stiffness model is developed to predict ultrasonic wave propagation through layered media. Model based inversion is used to study the bond quality evolution with layer build up. The objective is to form correlations between the power drawn during each individual layer, nondestructively measured bond quality, and destructive tests performed after manufacturing. This study is a step towards in-situ monitoring and closed loop control of the UAM process.
A-56: Microstructure-property Relations of Additively Manufactured 17-4 PH and 316L Steels: John Smugeresky1; Josh Sugar2; David Keicher2; 1Additive Manufacturing Materials Consultants; 2Sandia National Laboratories
The number of metals used with the Powder Bed Fusion (PBF) process to additively manufacture parts has been increasing. In this study, PH 17-4 and 316 steels were used. Samples of 17-4 PH have been processed before and after the fabrication of actual net shaped parts and the microstructure and properties characterized. The objective was to determine the ability of the process to maintain consistent and reproducible microstructure and properties over the course of the fabrication. An actual part made from 316 stainless steel and its support structure were sectioned, mounted, and the microstructures were compared for the same part fabricated on different PBF machines from the same manufacturer. The characterization consisted of metallographic sample preparation and examination using a range of experimental techniques. Results will be presented for several locations and orientations relative to the build direction, and compared to microstructure and properties of conventionally processed material.
A-57: Microstructure and Mechanical Properties of Ti-6Al-4V Additively Manufactured by Selective Electron Beam Melting: H. P. Tang1; Shenglu Lu1; Jian Wang2; 1Northwest Institute for Nonferrous Metal Research ; 2Northwest Institute for Nonferrous Metal Research
In this work, Ti-6Al-4V rods and plates were additively manufactured by SEBM. The as-built microstructure was consisted of martensite, massive phases and equilibrium α and β phases. It was found that the smaller size of the sample is, the more non-equilibrium phase (i.e., martensite) exists. Along the building direction, it was revealed that the microstructure is the coarsest and near equilibrium in the top segment, while it is the finest and non-equilibrium in the bottom area. Although there are some variances in tensile properties especially in ductility, all the tensile properties of the rods and plates meet the requirements specified by ASTM F3001-14. Post HIP was used to homogenize the microstructure and realized consistent tensile properties. Additionally, the authors gave future perspective on 3D printing of titanium alloys by SEBM.
A-58: Microstructure Evolution in Additively Manufactured Ti-6Al-4V Alloys: Joseph McKeown1; Rupalee Mulay1; Jeffrey Florando1; Mukul Kumar1; 1Lawrence Livermore National Laboratory
Additive manufacturing of Ti-6Al-4V alloys is of great interest due to the ability to process complex parts in their near net shape. This work examines microstructure and its evolution upon heat treatment in Ti-6Al-4V manufactured by selective laser melting (SLM). The microstructures of the additively manufactured (AM) alloys are compared to those of conventional wrought Ti-6Al-4V. Characterization of the microstructures was conducted using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The observed grain morphologies, crystallographic phases, and phase fractions as a function of processing conditions will be presented for the wrought, AM, and heat-treated AM alloys. The effects of processing/microstructure on mechanical properties will be discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.
A-59: Microstructure, Mechanical and Electrical Properties of Pure Metallic Microstructures Fabricated Using 3D Localized Electrodeposition: Majid Minary1; 1University of Texas at Dallas
In this presentation, we will discuss material, mechanical and electrical properties of free-standing micro-nano-structures of pure metal fabricated using 3D electrodeposition. In this technique a glass capillary with a few micron to sub-micron tip is filled with the electrolyte of a metal of interest. A liquid capillary formed between the tip of the pipette and the conductive substrate completes the electronic-ionic circuit. Upon application an appropriate electric potential metal ions reduce and get deposited on the substrate. The pipette is steered precisely in 3D using precision nano-positioners, which results in formation of desired 3D objects from a CAD file. The process is mainly driven by evaporation of the liquid in the meniscus bridge. We present fabrication of various metallic structures, as well as characterization of their materials, mechanical an electrical properties. A Multiphysics computational model will be also presented to explain the detailed mechanisms governing the process.
A-60: Modeling and Testing of ‘Fundamental Primitives’ in Metal Lattices Fabricated via Electron Beam Melting (EBM): Rachel Collino1; Tyler Ray1; Steven Wehmeyer1; Matthew Begley1; 1University of California, Santa Barbara
Additive manufacturing offers important advantages for the fabrication of metal lattices, notably those that exploit open cells to combine mechanical, thermal, or biological performance. The development of such meta-materials, especially those with optimized strut topologies, will rely critically on the ability to accurately and efficiently predict the performance of struts and nodes (‘fundamental primitives’). This talk will describe theory and experiments to characterize the mechanical behavior of simple Ti-6Al-4V strut connections, fabricated via EBM in an Arcam Q10plus. The results indicate regimes where strut intersections either behave rigidly or introduce compliance into the lattice. With this understanding, calibrated models of these fundamental primitives of cellular connections are used to predict the performance of larger, more complicated lattices. The benefits and challenges of this modular approach will be outlined, particularly with respect to the development of fast, accurate simulation tools that play a critical role in topology optimization.
A-61: Nanomechanical Characterization of Functionally Graded Al-Fe MMC Processed by Additive Friction Stir Processing: Paul Allison1; Oscar Rivera1; Zack McClelland2; Jianqing Su3; Nanci Hardwick3; 1University of Alabama; 2US Army ERDC; 3Aeroprobe Corporation
The Solid State Additive Manufacturing (SSAM) process referred to as Additive Friction Stir (AFS) provides a new path for repair, coating, joining and additively manufacturing materials such as functionally graded metal matrix composites (MMC). This additive manufacturing process differs from traditional friction stir welding since metal powder or solid rod is fed through a non-consumable rotating cylindrical tool generating heat and plastically deforming the feedstock material through controlled pressure from the tool as successive layers are built upon a substrate. In this research, aluminum powder was mixed with iron particles and deposited on an 1100 aluminum alloy substrate with the iron content varying from 2%-iron at the base to 24%-iron at the top of the build. Nanoindentation performed on the deposited MMC was spatially correlated to scanning electron microscopy – energy dispersive X-ray spectroscopy (SEM-EDX) to provide a relationship of the nanomechanical modulus and hardness to the indent chemical composition.
A-62: Numerical Investigation of Surface Morphology with Different Laser Scanning in Selective Laser Melting: Yu Che Wu1; Weng Sing Hwang1; Cheng Hung San2; Yang Shan Lin2; Chih Hsiang Chang2; 1National Cheng Kung University (NCKU); 2Industrial Technology Research Institute (ITRI)
Re-solidified surface morphology in additive manufacturing is difficult to predict up to now. In this study, a three-dimension numerical model of selective laser melting is developed to investigate the phase transformation behaviors for Ti6Al4V, which coupled with phase change and free surface mechanisms by volume-of-fluid method. The parametric study of the laser scanning speed, melt pool dynamics, surface tension and surface morphology are proposed to discuss in this research. The simulation reveals that surface tension which driven the melt pool plays an important role in material melting course of events. To compare the parametric study in different laser scanning speed, the quantify factors as melt pool length, melt pool width and penetration depth show the inverse relationship between the quantify factors and laser scanning speed. On the other hand, shrinkage ratio corresponds to estimate the surface quality. The simulation result shows a good agreement with the experimental data.
A-64: Physics-based Surrogate Model for Uncertainty Quantification of Single Track Geometry in Selective Laser Melting: Alexander Wolfer1; Umberto Scipioni Bertoli2; Kevin Wheeler3; Dogan Timucin3; Manyalibo Matthews4; Saad Khairallah4; Andrew Anderson4; Rose McCallen4; Julie Schoenung2; Jean-Pierre Delplanque1; 1University of California, Davis; 2University of California, Irvine; 3NASA Ames Research Center; 4Lawrence Livermore National Laboratory
Statistically-based qualification of additive manufacturing processes presents sizeable challenges associated with the time and cost required in the production of the needed test data. In this work, a model-based Bayesian uncertainty quantification (UQ) framework is used to account for various sources of uncertainty in the prediction of the geometry of single tracks produced using selective laser melting (SLM). Due to the multi-physics complexity of the SLM process, the most accurate numerical simulations require prohibitive computational times, and are unusable in the context of typical UQ techniques. Instead, we present a physics-based surrogate model that is simplified and computationally efficient while still accounting for the key physics needed to quantify the overall uncertainty of the process. This surrogate model takes into account the effect of powder characteristics such as size distribution and morphology on light absorption and heat conduction in the powder layer to assess track geometry. This work was performed under the auspices of the U.S. Department of Energy by Lawerence Livermore National Laboratory under Contract DE-07NA27344.
A-65: Plasticity and Damage Modeling Capturing Strain-rate and Stress-state Effects of Solid State AFS Additive Manufactured Aluminum Alloys
: Oscar Rivera1; Omar Rodriguez1; J. Brian Jordon1; Zackery McClelland2; Jianqing Su3; Nanci Hardwick3; Paul Allison1; 1The University of Alabama; 2US Army ERDC; 3Aeroprobe Corporation
The Solid State Additive Manufacturing process referred to as Additive Friction Stir (AFS) that fabricated the samples in this study provides a new path for repair, coating, joining and additive manufacturing of metals and metal matrix composites. In this research, a microstructure-based internal state variable (ISV) plasticity-damage model was used to model the mechanical behavior of AFS 2219 aluminum alloy. Electron Backscattered Diffraction (EBSD) was used to characterize the as-fabricated microstructure, where a fully-dense equiaxed grain morphology with finer grains formed by dynamic recrystallization (DRX) was observed. Micro-hardness mapping of the as-built structures and monotonic tension and compression experiments at both quasi-static (0.001/s) and dynamic (2500/s) strain rates were performed to obtain the set of plasticity and damage constants necessary to capture the strain rate and stress state behavior of this additive material. The high rate experiments exhibited increased flow stress when compared to the quasi-static experiments, as expected.
A-66: Post-processing Effects on AM Pore Geometry: Richard Fonda1; Amanda Levinson1; David Rowenhorst1; 1Naval Research Laboratory
Additive manufacturing (AM) holds tremendous promise for a wide variety of applications, but current practices still generate pores within the AM structure that can be detrimental to performance. This presentation will discuss the morphology and distribution of pores generated within the AM structure as revealed by 2D analyses of cross section surfaces and 3D characterization using X-ray computed microtomography (XCMT), and the evolution of those pore structures during thermo-mechanical post-processing procedures such as hot isostatic pressing (HIP) and heat treating. Structure-property relationships will then be explored using mechanical testing.
A-68: Process Parameter Optimization Strategy for Ni-based Superalloy in Electron Beam Melting Additive Manufacturing: As-built Part Quality and Microstructure: Yousub Lee1; Mike Kirka1; Alfredo Okello1; Jake Bultman1; Naren Raghavan2; John Turner1; Ryan Dehoff1; 1Oak Ridge National Laboratory; 2University of Tennessee
Electron Beam Melting (EBM) additive manufacturing involves complex thermal characteristics stemming from different process parameters, which significantly influence as-built quality and microstructure. However, the thermal variations during deposition have not been fully understood due to lack of experimental measurement for EBM process. The optimization of the process highly requires an understanding of melt pool geometry and temperature distribution. A three dimensional transient numerical model is used to capture thermal profile and melt pool geometry at the EBM process. The parameters of scan velocity, focus offset, line offset and line order are systematically varied to find an optimal condition of EBM process in a Ni-based superalloy. Later, the predicted results are utilized to quantitatively study the effect of scan velocity, focus offset, line offset and line order on the formation of defects and as-built surface quality. The internal porosity and surface topology are characterized using optical microscopy and image processing software.
A-69: Processing-structure-property Correlation for Fused Deposition Modeling of Graphene-polylactic Acid Composites: Pranjal Nautiyal1; Daniela Montero Zambrano1; Benjamin Boesl1; Arvind Agarwal1; 1Florida International University
Graphene-Polylactic Acid (Gr-PLA) composites are fabricated by Fused Deposition Modeling (FDM), employing a novel composite filament. Printed layer morphology of Gr-PLA is compared with pure PLA to assess the influence of graphene on polymer curing during printing. Effect of printing speed and temperature on the material morphology is also studied to evaluate the influence of processing parameters on the morphology of material being printed. Tensile tests and post tensile microscopic examination is carried out to determine the mechanical strengths and deformation mechanisms. Since PLA is a material suitable for orthopedic applications, osseo-integrable cellular scaffolds of pure PLA and Gr-PLA are also printed and their response to compressive loading is probed. Deformation mechanisms are studied by electron microscopy.
A-70: Production and Additive Manufacturing of TiNi Powders by PREP: Gang Chen1; Jingou Yin1; Nan Liu1; Huiping Tang1; Muhammad Dilawer Hayat2; Peng Cao2; 1Northwest Institute for Nonferrous Metal Research; 2The University of Auckland
In this study, we fabricated spherical TiNi powders using plasma rotating electrode process. Scanning electron microscopy, X-ray diffraction and differential scanning calorimetry were extensively performed to investigate the microstructure of atomized TiNi powders. Tensile properties were characterized for TiNi parts made by selective electron beam melting. The results show that the powders exhibit B2 TiNi as the main phase, while powders with different particle sizes yield various martensitic transformation temperatures and different transformation steps. The additively manufactured TiNi mainly show B2 phase and sound superelasticity.
A-71: Recylability Study on a Gamma-TiAl Alloy for use in Electron Beam Melting Additive Manufacturing: Peeyush Nandwana1; Ryan Dehoff1; William Peter1; 1Oak Ridge National Laboratory
gamma-TiAl based alloys are candidate high temperature materials, but have found limited use owing to their poor machinability. Owing to their poor machinability, these alloys are well suited for fabrication via additive manufacturing (AM) techniques. Laser based techniques cause cracking in gamma-TiAl components resulting from high residual stresses. Electron beam melting (EBM) is a more viable technqiue for fabrication of such alloy systems. However, since the processing is carried out under vacuum and at elevated temperatures, there is a higher tendency for loss of high vapor pressure elements like Al, and Cr. The present work focuses on a recyclability study wherein the powder will be subjected to the electron beam over multiple processing cycles to understand the change in feedstock chemistry over time. This study will establish a guideline for maximizing the use of powders while keeping the alloy chemistry and subsequently properties within the required specifications.
A-72: Relating Crack Formation to Process Parameters in MarM-247 Fabricated by Electron Beam Melting: Christopher Romanoski1; Michael Kirka2; 1Vanderbilt University; 2Oak Ridge National Laboratory
High gamma prime containing nickel base (Ni-base) superalloys represent a defining class of materials that have the ability to operate in high-temperature, high-stress, and corrosive environments while maintaining creep, fatigue, and fracture resistance. These unique properties are attributable to the highly engineered alloy compositions and associated precipitate strengthened microstructure. However, it is these attributes that make it difficult to utilize additive manufacturing techniques to fabricate components of increased complexity over that of traditionally manufactured components due to the crack proneness of the alloy family. To successfully fabricate high gamma prime containing Ni-base superalloys with AM techniques, the process must be optimized and understood to mitigate cracking in the alloy during the build process. To be presented is an analysis relating the cracking susceptibility of the gamma prime containing alloy MarM-247 to processing conditions in the electron beam melting process and the necessary processing space to mitigate cracking.
A-73: Report on a Large Collaborative Project Focused on Capturing all AM Process and Build Data for Combination with an ICME Ready Software Environment Driving towards Certification: Will Marsden1; Deborah Mies1; 1Granta
Additive Manufacturing has been shown to meet demanding part requirements and in a time frame not previously realized. It is arguably the first real incarnation of ICME. However, production of consistent, high-quality and certifiable parts continues to be the biggest hurdle to maturing the industry – especially for critical aerospace applications. Capturing the layer-by-layer details of the build process in an integrated system is the critical first step to gaining a necessary understanding of the interaction between the input geometry, material and process variables and resultant local materials properties. When extended across material length scales and integrated with analysis and simulation tools, it provides the basis for real-time process monitoring and adjustment mechanisms that ensure that the desired properties are consistently achieved. This presentation reports on a large scale collaborative effort that has generated a multi-scale digital platform to capture process data, predict failure modes and ensure reproducible parts.
A-74: Stainless 316L Powder Recyclability and Oxygen Pickup as Applicable to Selective Laser Melting (SLM): Daniel Galicki1; Fred List2; 1University of Tennessee/Oak Ridge National Laboratory; 2Oak Ridge National Laboratory
In laser powder bed additive manufacturing processes, feedstock materials are often recycled after each build. This recycling decision assumes minimal pick up of gases like oxygen by un-melted metallic powders. Currently, a knowledge gap exists in the fundamental understanding of how the powder size distribution, morphology, and chemistry changes resulting from re-use affect the subsequent component properties and the flowability of the powder. Initial findings from experimental trials with stainless steel 316L have indicated significant oxygen pickup in molten material ejected from the powder bed surface (0.186 wt%) compared to feedstock powder (0.032 wt%). X-Ray diffraction analysis has also confirmed the presence of a magnetic ferritic (BCC) phase intermixed with the predominantly austenitic (FCC) phase within the re-solidified ejecta material. Excessive oxygen pickup by recycled powder may affect the pool shape and molten metal convection of the micro-weld and initiate the precipitation of unwanted oxides within the as-built metal part.
A-75: Systematic Approach to Quantifying the Anisotropic Elastic Modulus of FDM Materials: Sven Voigt1; James McGuffin-Cawley1; Jennifer Carter1; 1Case Western Reserve University
Fused deposition model (FDM) amorphous polymer tools are increasingly used in small-batch, sheet metal forming (SMF) operations, such as hydroforming and stretch-forming. “Sparse build styles” offer time and cost savings by adjusting the parameters to leave significant interior volumes empty. Predicting mechanical performance is strongly dependent on the wide range of processing parameters, materials, and geometries. In this study, orthotropic properties as a function of FDM build sparseness were explored. Full field strain mapping with digital image correlation coupled with macroscale compression testing was utilized to quantify stiffness and yield tensors. The time dependence of polymer properties required testing at strain rates that produced tensors relevant to the SMF operations being studied. These tensors were implemented into finite element models to simulate the orthotropic elastic and shear behavior under SMF pressure application.
A-76: The Effect of Laser Energy Density on the Microstructure and Mechanical Properties of Ti-6Al-4V alloys by Selective Laser Melting: Dang Khoa Do1; Peifeng Li1; 1Nanyang Technological University
The systematic experiments with thermal simulation and quantitative analysis were conducted to investigate the microstructure and mechanical properties of selective laser melted (SLM) Ti-6Al-4V alloys as a function of laser energy density. The SLM Ti-6Al-4V alloys consist of nearly complete fine acicular martensites α’ crossing one another and retain columnar β grains due to high cooling rate. Prior columnar β grains grow continuously from the bottom heading outward the centreline of the sample, in the opposite direction to the heat conduction flow. Thermal simulation shows relatively low cooling rate in the centre of sample, thus resulting in coarser grains. It was also found that higher laser energy density tends to increase grain width and martensitic lath size, form higher volume of macro-twins and thus improve mechanical properties.
A-77: The Effect of Surface Finish on Performance in Additive Manufacturing: Joy Gockel1; 1Wright State University
An understanding of the effect of as built surface conditions produced by additive manufacturing (AM) on the mechanical properties is important to take advantage of complex geometries with un-machined internal surfaces. Direct metal additive manufacturing is used not only for prototyping, but also to produce final production parts. Due to the inherent layered nature of the process, a rough surface is present which provides many potential crack initiation sites. Often, process parameter optimization is misguided by average values that do not capture property limiting behavior. This work investigates a range of different surface features that are produced in AM processing using a laser powder bed fusion process. Finite element modeling is then used to determine which surface features will provide the highest stress concentration. This understanding will ultimately be used to guide process optimization and determine which surface feature measurements are necessary to predict mechanical performance.
A-79: Understanding the Role of Process Variables on Mechanical Properties: Wes Everhart1; Paul Korinko2; John Bobbitt2; Marissa Reigel2; Michael Morgan2; 1Honeywell National Security Campus; 2Savannah River National Laboratory
In order for additive manufacturing to be widely accepted, the influence of both direct and indirect variables on processes needs to be understood. For this study, Selective Laser Melting process using Type 304L stainless steel is being characterized to understand the variables of build location, nearest neighbor, and build group on mechanical properties. Samples were built in near net shape and were tested in the as-fabricated condition. Samples from three different builds were used to determine the fatigue, tensile, torsion, Charpy impact and fracture toughness properties. These results indicate that the properties are influenced by many variables that may be considered secondary or higher order. They further indicate that SLM can be used for select components; however, understanding the process variables and their influence on properties is still an evolving field. This study and other like it are needed for additive manufacturing to be considered for high value added components.
A-80: Vapor Bath Treatment of Fused Filament ABS for Fatigue Life Improvement: Taylor Tosaya1; Michael Maughan1; 1University of Idaho
3D printed or additively manufactured plastic parts have myriad uses, however they often lack the necessary properties for structural or service applications. Frequently this constraint is not one of strength, but one of fatigue life. In order to improve fused filament ABS plastic part performance, a vapor bath treatment technique is evaluated via the rotating bend test for fatigue life. A comparison of service life, surface morphology, and failure modes for treated and untreated specimens will be discussed.
A-82: In-Process Layer-by-layer Surface Characterization of Metals Fabricated using Laser Engineered Net Shaping (LENS): Andrew Kustas1; David Keicher1; Michael Brumbach1; Brendan Nation1; Nicolas Argibay1; 1Sandia National Laboratories
Widespread commercial adoption of metal additive manufacturing (AM) technologies is limited largely due to part and process variability. Limited understanding of the correlations between processing parameters (e.g., laser power, build velocity, print pattern, etc.) and process signatures (e.g., temperature and geometry of the melt pool and solidified material) remains a challenge to reducing this variability through process controls. Recent efforts have focused on developing in situ/in-process characterization tools to start linking these correlations and eventually enable effective process control. Relatively few studies have focused on establishing connections between processing parameters, processing signatures and solidified layer defects. We present a demonstration of real time in-process surface topography measurements during a laser engineered net shaping (LENS) operation using a confocal chromatic white light line sensor (CCWLLS). This technique rapidly generates high resolution (~ 2 µm lateral, 80 nm axial), 3-D surface reconstructions of each build layer. Potential of utilizing this instrument to establish quantitative structure-property relationships derived from in-process high-resolution multi-scale surface metrology and ex situ characterization of AM metal parts is also discussed.