Additive Manufacturing: Materials Design and Alloy Development II: Poster Session
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Additive Manufacturing Committee, TMS: Integrated Computational Materials Engineering Committee
Program Organizers: Behrang Poorganji, Morf3d; James Saal, Citrine Informatics; Orlando Rios, University of Tennessee; Hunter Martin, HRL Laboratories LLC; Atieh Moridi, Cornell University
Monday 5:30 PM
February 24, 2020
Room: Sails Pavilion
Location: San Diego Convention Ctr
A-77 (Digital): Understanding Cellular Structures in Additively Manufactured 316L: Richard Fonda1; Joseph Aroh2; Jerry Feng1; David Rowenhorst1; 1Naval Research Laboratory; 2Carnegie Mellon University
It is critical to understand the multiscale microstructural evolution of additively manufactured materials in order to accurately model their responses and behavior. One prominent feature that needs to be better understood is the fine cellular structure that underlies the coarser grain structure in laser powder bed fusion AM 316L builds. These cellular structures have been associated with the observed enhancements in as-built properties, but their origins and characteristics are not well understood. The cellular features have aspect ratios ranging from equiaxed to very elongated and often exhibit multiple cell orientation domains within a single grain. We have systematically characterized these cellular features to reveal their crystallography, orientation, and shape. We will discuss the characteristics of these cellular structures and how they relate to the local crystal growth direction, thermal gradient, and overall build direction.
A-49 (Invited): Additions of Iron to Grain Refine Ti Alloys during Laser Powder Bed Fusion: Marco Simonelli1; Nesma Aboulkhair1; Yau Yau Tse2; Adam Clare1; Richard Hague1; 1University of Nottingham; 2Loughborough University
There remains a significant challenge in adapting alloys for metal based Additive Manufacturing (AM). Adjusting alloy composition to suit the process, particularly under regimes close to industrial practice, is therefore a potential solution. With the aim of designing new Ti-based alloys of superior mechanical properties for use in laser powder-bed fusion, this research investigates the influence of Fe on the microstructural development of Ti-6Al-4V. The operating mechanisms that govern the relationship between the alloy composition (and Fe in particular) and the grain size are explored using EBSD, TEM and in-situ high energy synchrotron X-ray diffraction. It was found that Fe additions up to 3wt% lead to a progressive refinement of the microstructure. By exploiting the cooling rates of AM and suitable amount of Fe additions, it was possible to obtain microstructures that can be optimized by heat treatment without obvious precipitation of detrimental brittle phases. The resulting microstructure consists of a desirable and well-studied fully laminar α+ β structure in refined prior-β grains.
A-50 (Invited): Alloy Development Feeder for Accelerated Materials Development: Kevin Luo1; Melanie Lang1; Jeff Riemann1; 1FormAlloy
With the rapid growth in additive technologies, there is a need for materials and material systems development to keep pace. To accelerate materials development and allow the progress to be utilized by additive technologies, FormAlloy designed and developed the ADF Alloy Development Feeder to enable rapid deposition of up to 16 different alloys or alloy blends. Utilizing a revolver-style motion, each powder vial can be accessed and deposited quickly and efficiently. Custom alloys can developed by blending existing alloys or elemental powders in designated ratios and deposited by additive technologies like Directed Energy Deposition (DED). Functionally graded material (FGM) systems can be executed easily in a predetermined deposition strategy. Discover how the FormAlloy ADF works and how it reduces alloy development time by orders of magnitude.
A-51: Additive Manufacturing of Atomized Ti-1Al-8V-5Fe by Laser Powder Bed Fusion: Eugene Ivanov1; Eduardo del Rio1; Aaron Marshall2; Vivian Hogan2; Daniel Satco3; Ayman Salem3; 1Tosoh SMD Inc; 2Materials Resources, LLC; 3Material Resources LLC
The inherent fast cooling rates during laser powder bed fusion (LPBF) of Ti-185 solve the segregation problem of the casted material during. The design flexibility of AM combined with the high-strength and ductility of the heat-treatable Ti-185 opens the doors to many applications. The atomized powder for AM was not available before the current work. To establish the data for use of the alloy, characterization of the atomized powder will be presented followed by evaluation of the mechanical properties after LPBF in the as-built, heat-treated, and after hot isostatic pressing (HIP) conditions. Room temperature tensile testing of the as-built Ti-185 resulted in 1022 MPa UTS, 84 GPa Young’s modulus and 8.3% ductility. HIP treatment followed by annealing increased the UTS and Young’s modulus to 1327MPa and 107 GPa , respectively, while decreasing ductility to 4.5%. Microstructure evolution of the as-built Ti-185 after heat treatment and HIP will also be shown.
Cancelled
A-52: Advancing Printability of Materials through Laser Metal Additive Manufacturing: Sofia Sheikh1; Raymundo Arroyave1; 1Texas A&M University
Laser metal additive manufacturing (AM) is a growing research field due to the design freedom it provides. However, the uncertainty associated with the fabrication process of an AM system due to the various processing parameters (e.g laser power, scan velocity and hatch spacing) and thermal properties of the material (e.g. surface absorptivity, latent heat of fusion and solidification range) is still a concern. Processing maps based on laser power versus scan velocity are calculated using a thermal model in COMSOL ® Multiphysics. The processing maps are used to predict regions where balling, keyholing, lack of fusion can be predicted. Using the maps, a correlation between the material thermal properties and the macro-failures were investigated to determine how the regions of macro failures can be decreased.
A-53: Automatically Quantifying Phase Information from HRTEM for Additively Manufactured Inconel 718: Sen Liu1; Behnam Aminahmadi1; Branden Kappes1; Aaron Stebner1; Xiaoli Zhang1; 1Colorado School of Mines
Additive manufactured (AM) metals have a unique initial microstructure that requires custom heat treatments. Inconel 718 precipitation strengthening relies on the coprecipitation of γ' and γ'' phases. High resolution transmission electron microscopy (HRTEM) has been used to track precipitation growth behavior during post processing. Identifying nanoprecipitates evolution during heat treatments requires hundreds of images and thousands of precipitates. Computer vision (CV) coupled with machine learning (ML) segmentation automatically extract and quantify phase information with angstrom-scale resolution, allowing for quantitative correlation between nanostructure formation and processing conditions. We introduce a sliding Fast Fourier Transform (FFT) to automatically segment unique phases from HRTEM. The image processing used is largely insensitive to image variations. An unsupervised ML was used to automatically group similar phases, which is unique to composition and orientation of constituent phases. This study shows the promise of ML for enabling high-throughput materials characterization to accelerate AM materials development.
A-54: Ball-milled CoCr + X (X=WC or SiC) Composite Powders for Additive Applications: Madelyn Madrigal1; Suveen Mathaudhu1; Guillermo Aguilar1; 1University of California, Riverside
The field of metal additive manufacturing (MAM) is rapidly advancing; however, it faces several challenges including the development and production of new alloy systems and powder composite manufacturing methods. Previous studies have investigated metal matrix composites produced by selective laser melting (SLM) which resulted in finer grains, improved hardness, and tensile strength due to the homogeneous distribution of reinforcement particles. This study investigates the viability of ball milling and laser sintering for CoCr composites reinforced by WC or SiC dispersoids. The particle size, flowability, microstructure, and composition of the CoCr-WC and CoCr-SiC powders are compared with post sintered samples to probe the microstructural evolution during laser processing. The observations point to the applicability of high energy ball milling as a platform for alloy and composite design for MAM.
A-55: Cold Spray Deposition of Aluminum onto Polymer and Composite Substrates: Reza Rokni1; Po-Lun Feng1; Steve Nutt1; 1University of Southern California
Fully dense CS deposits of 7075 Al and commercial purity (CP) Al were achieved on PEEK, PEI, and PEKK 30% carbon fiber substrates, using an iterative optimization process. For CS onto thermoplastic substrates, 7075 Al deposits showed low deposition efficiencies (DEs) and low thicknesses but high adhesive strengths, while CP Al deposition resulted in high DEs and thicknesses but relatively low adhesive strengths. For CS onto PEKK 30% carbon fiber, deposition with N2 led to greater thicknesses (e.g., greater DEs) and adhesive strengths compared to using He. These variations are influenced by two main factors. The first factor is the differences in material properties between coating and substrate, which can affect the depth of penetration of impacting particles and residual stress at coating/substrate interface. The second factor is the selected CS process parameters because first few layers and build-up layers may require different process conditions.
A-56: Compression Behavior of Additively Manufactured High Entropy Alloy with Transformation Induced Plasticity: Saket Thapliyal1; Saurabh Nene1; Priyanshi Agrawal1; Rajiv Mishra1; 1University of North Texas
Metastable high entropy alloys (HEAs) are known to exhibit local variation in work hardening near defects due to stress induced γ→ϵ transformation. Such phenomenon has been used in this study to design damage tolerant alloys for laser powder bed fusion (LPBF) additive manufacturing (AM) which often produces parts with some level of porosity. A Fe40Co21.5Mn19.2Cr14.7Si2.8Cu1.8 HEA (Cu-HEA) which shows metastability-promoted γ→ϵ transformation has been processed with LPBF-AM. The as-built samples were tested under compression at different strain levels and the results were compared with as-cast and wrought microstructures. Microstructural characterization of AM samples showed that ϵ phase percentage increased to 68% from an initial phase percentage of 2% upon compression at 40% strain level thereby confirming transformation induced plasticity in Cu-HEA.
A-57: Design of Easy-to-Use Structural Alloy Feedstocks for Additive Manufacturing Using Machine Learning Methods: Akansha Singh1; Ben Rafferty2; Jeremy Iten2; Jacob Nuechterlein2; Branden Kappes1; Sridhar Seetharaman1; Aaron Stebner1; 1Colorado School of Mines; 2Elementum 3D
Metal additive manufacturing is a multi-process and machine dependent complex procedure and requires a specialist to manufacture a part. We are trying to design an alloy feedstock which should be easy to print and consistent regardless of the machine, and also whose manufacturing requires minimal trained members and uses a minimum set of processing tools. For this, we identified several descriptors such as mushy zone width, thermal expansion, miscibility gap, etc., to define printability. We performed several CALPHAD based computer simulations on iron-based alloys and gathered a large dataset for alloy compositions, and their thermodynamic properties. In order to relate alloy compositions, stable phases and their properties to the descriptors of printability, we employed machine learning methods and estimated the associated error in the predictions. Using our developed model, we would be able to design the alloy feedstock with highly printable, functional, and reproducible printed properties.
A-58: Development of Laser Parameters for Pure Copper with Parts Fabricated from Laser Powder Bed Fusion (PBF): Michael Brand1; Colt Montgomery1; Robin Pacheco1; Amber Black1; Ryan Mier1; 1Los Alamos National Laboratory
Copper is a soft, malleable, and ductile metal with very high thermal and electrical conductivity, which is widely used in industries such as aerospace, automotive, and electronics. However, the vast majority of additive copper is currently based on alloys of copper, not the pure metal. Pure copper has a high laser reflectance rate, over 90% with standard laser based AM systems making it difficult for the laser to continuously melt pure copper powder, which leads to interface failure and thermal cracking. Specific Laser Parameters were developed on the EOS M290 powder bed fusion (PBF) using single beads and density cubes to achieve a fully dense sample. With these parameters, the single beads and the density cubes were viewed using an optical microscope and scanning electron microscope (SEM) to verify that the copper is fully melting.
A-59: Development of Metallic Glass Micro-wires for the Direct Laser Melting Deposition Process: Song-Yi Kim1; A-Young Lee1; Hanuel Jang1; Hwi-Jun Kim1; Chang-Woo Lee1; Min-Ha Lee1; 1KITECH
In this study, the metallic glass micro-wires which had micrometer scale in diameter with circular cross section were produced by melt-extraction method. Various compositions of metallic glasses, such as Co-based, Ni-based, Fe-based and Cu-based amorphous alloy wire, were synthesized using by melt extraction method, respectively. The metallic glass layers were deposited using laser melting additive manufacturing technique to investigate the effect of laser power on the deposition of metallic glass micro-wires. It was found that the mean width of deposited layer is expanded with increasing laser power attributed to a change in the wettability. The micro-hardness value of metallic glass deposited layer was higher in low power deposition. The reliability for the optimization of processing parameters to control micrometer scale deposition by metallic glass wire is also evaluated.
A-60: Effect of Laser Glazing on Quasicrystals in Powder-processed Icosahedral-phase-strengthened Aluminum Alloys: Mingxuan Li1; Hannah Leonard1; Sarshad Rommel1; Thomas Watson2; Tod Policandriotes3; Mark Aindow1; 1University of Connecticut; 2Pratt & Whitney; 3Collins Aerospace
Recently, we have developed an Al-Cr-Mn-Co-Zr alloy that exhibits a nano-composite FCC Al plus I-phase microstructure in gas-atomized powder. This microstructure is retained during consolidation of the powder to form bulk material. This consolidated material was subjected to surface laser glazing with scan rates ranging from 0.2 m/s to 1.2 m/s and powers ranging from 180 W to 330 W, and the effects of these process parameters on the resulting microstructure were evaluated. At low scan rate and high power, coarse pseudo-dendritic dispersoids were found in the melt pool. With increasing scan rate and decreasing power, smaller spherical precipitates formed. At the highest scan rate and lowest power, the melt pool consisted of a single solid solution phase. The microstructures and chemical compositions of the phases were characterized using scanning electron microscopy and transmission electron microscopy. Finally, the possibility of additive manufacturing for these metal matrix composites was evaluated.
A-61: Exploring Rapid Solidification in Additive Manufacturing through Splat Quenching: Zachary Hasenbusch1; Sydney Morales1; Luke Brewer1; Laurentiu Nastac1; Andy Deal2; Ben Brown2; 1University of Alabama; 2Kansas City National Security Campus
This presentation will discuss the use of splat quenching (SQ) method to simulate rapid solidification conditions present in fusion-based additive processes. Splat quenching experiments produce cooling rates typically between 10^5 and 10^6 °C/s and enable the measurement of fundamental, rapid solidification parameters. This method is being applied to 316 stainless steel and variants with several starting superheat temperatures and corresponding cooling rates. A combination of x-ray spectroscopy and electron backscatter diffraction is used to determine how these very high cooling rates alter the solidification path and key solidification parameters. In particular, changes to the partition coefficients of the alloying elements will be determined. The experimental results will be compared with finite element simulations of heat transfer during the splat quench process. This work was funded by the Department of Energy’s Kansas City National Security Campus which is operated and managed by Honeywell Federal Manufacturing Technologies, LLC under contract number DE-NA0002839.
A-62: High-temperature Compressive and Creep Properties of Equiatomic CoCrFeMnNi High-entropy Alloy Manufactured by Selective Laser Melting: Kee-Ahn Lee1; Young-Kyun Kim1; Sangsun Yang2; 1Inha University; 2Korea Institute of Materials Science
An equiatomic CoCrFeMnNi high-entropy alloy (HEA) was manufactured by using selective laser melting (SLM), and its microstructure, high-temperature compressive and high-temperature creep properties were investigated. SLM-built equiatomic CoCrFeMnNi HEA shows dislocation networks, strongly-oriented grains and nano-sized precipitates. It was found that the SLM-built HEA has superior yield-strengths at all temperature ranges compared with cast- and wrought-HEAs. In particular, YS difference between SLM-HEA (551 MPa) and cast-HEA (119 MPa) was 432 MPa at 600 °C. Slip and deformation twin behaviors were observed at temperature ranges up to 600 °C, but above 700 °C, slip and partial-recrystallization occurred. SLM-built HEA shows excellent high-temperature creep resistance compared with cast- and recrystallized-HEAs in all stress ranges. Viscous glide motions of dislocations dragging solute-atmospheres was detected at relatively lower stress conditions but different creep mechanism (climb) appeared at higher stress conditions. Correlations between microstructure, high temperature deformation and creep mechanisms were also discussed.
A-63: Hybrid Additive Manufacturing of MS1-H13 Steels via Direct Metal Laser Sintering: Sajad Shakerin1; Mohsen Mohammadi1; 1Marine Additive Manufacturing Centre of Excellence (MAMCE)
A bimetal steel was additively manufactured by depositing maraging steel powder (MS1) on top of a tool steel H13 through the direct metal laser sintering technique (DMLS). The microstructure and interfacial morphology of the hybrid MS1-H13 steel were characterized using optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), and electron backscatter diffraction (EBSD). Uniaxial tensile and microhardness tests along with fractography of the fracture surfaces were carried out to investigate the mechanical behavior of the hybrid MS1-H13 steel. The results showed that no cracks or porosities were formed at the interface proving the reliability of the hybrid MS1-H13 steel. The interface between the DMLS-MS1 and the underlying H13 tool steel was as narrow as 2µm. The microhardness tests across the interface revealed an abrupt increase of the hardness on the printed side leading to a stronger interface.
A-64: Investigating Solidification and Liquation Cracking in AA7075 Electron Beam Freeform Fabrication Deposits: Mary Cecilia Mulvaney1; James Fitz-Gerald1; Marcia Domack2; Karen Taminger2; 1University of Virginia; 2National Aeronautics and Space Administration
Airframe manufacturers have long sought an aluminum alloy (AA) that is compatible with additive manufacturing (AM) methods such as electron beam freeform fabrication (EBF3) and that offers strength levels comparable to AA7050. Currently, composition-driven solidification and liquation cracking deem high-strength, wrought 7xxx-series AAs ‘unweldable’ in fusion-based AM processes. This research investigated cracks and alloying element losses that limit the compatibility of 7xxx-series aluminum with EBF3. AA7075 linear deposits were fabricated with EBF3 on 0.25” or 1” baseplates at an energy density of 24 kJ/cm3. Fractographic analysis revealed solidification cracking across most deposits, with periodic, surface-breaking cracks accentuated by increased baseplate thickness. X-ray computed tomography (XCT) showed internal liquation cracks initiating directly below the final layer of most deposits, a result of the contracting molten pool straining the partially-melted zone of a previous layer. Correlations were noted between the extent of vaporization of Zn and Mg and that of cracking.
A-65: Isotropic Microstructure and Mechanical Properties of Additively Manufactured Ti-based Alloy: Gwanghyo Choi1; Won Seok Choi1; Pyuck-Pa Choi1; 1Korea Advanced Institute of Science and Engineering (KAIST)
Direct laser deposition (DLD) is a metal-based additive manufacturing (AM) technique, also referred to as laser-based direct energy deposition (DED). This manufacturing technique enables to make the physical realization of 3D model data via involving incremental layer-by-layer deposition, as opposed to subtractive manufacturing methodologies. The deposition is conducted by fusing metallic powders with a high-energy laser. We obtained non-columnar microstructure and random texture via modifying powder mixtures and processing parameters. The ratio of powder mixtures and processing parameters were optimized by means of high-throughput laser-aided fabrication. This resulted in isotropic mechanical properties irrespective of deposition direction. The thermodynamic stability of intermetallic phases was controlled by alloying composition in order to improve the material toughness. We also investigated the influence of alloying composition on microstructure of deposited materials. This study suggests an alloy design concept for additive manufacturing and provides a viable route for tailoring microstructure and mechanical properties.
A-66: Laser Powder Bed Fusion of a High Entropy Alloy Enabled with Transformation Induced Plasticity: Priyanshi Agrawal1; Saket Thapliyal1; Rajiv Mishra1; 1University of North Texas
Laser powder bed fusion (LPBF) additive manufacturing (AM) is an enabling technology but is currently hindered by limited availability of printable materials with high strength and ductility. In this study, we have printed a new high entropy alloy (HEA) that exhibits transformation induced plasticity (TRIP). Effect of various printing parameters, i.e. layer thickness, hatch spacing, power, and scan speed on part density, microstructure and mechanical properties have been evaluated. These parameters were optimized to obtain fully dense, homogenized material with minimal defects. The effect of parameters on the phase stability of HEA will be discussed and correlation of the mechanical response with microstructure will be presented.
A-67: Nickel Free Stainless Steels Powders Designed for Laser Based Powder Bed Fusion Intended for Implantable Devices: Bernice Gatrell1; Colton Steiner1; Ron Aman2; Nader Dariavach1; Jason Lehrer3; 1Johnson & Johnson; 2Carpenter Technology Corp.; 3Carpenter Technologies Corp.
CoCrMo alloys have a long successful clinical history both in the orthopaedic and dental industry for implantable devices. There is interest in the orthopaedic industry to investigate alternative alloys for patients who may be allergic to elements found in CoCrMo alloys, such as Cobalt, Chromium and although only found as a trace element, Nickel. Johnson & Johnson 3D Printing Center of Excellence has partnered with Carpenter Technology Corporation to develop two nickel-free stainless-steel alloys for Additive Manufacturing. One alloy is known as CarTech® BioDur 108 and the second alloy is new, simply referred to Ni-Free AA (Alternative Alloy). Both materials are atomized to produce powder for experimentation using the additive manufacturing technology, laser-based powder bed fusion (LPBF). LPBF parameter will be optimized. Static mechanical properties, chemistry, density and microstructure will be presented.
A-68: On The Effect of Building Direction on the Microstructure and Grain Morphology of a Selective Laser Melted Maraging Stainless Steel: Mehdi Sanjari1; Amir Hadadzadeh1; Ayda Shahriairi2; Saeed Tamimi3; Hadi Pirgazi4; Babak Shalchi Amirkhiz5; Leo Kestens4; Mohsen Mohammadi2; 1University of New Brunswick; CanmetMATERIALS; 2University of New Brunswick; 3AFRC- University of Strathclyde; 4Ghent University; 5CanmetMATERIALS; University of New Brunswick
In this study, cylindrical rods of a low carbon Fe-Cr-Ni-Al maraging stainless steel (CX) were fabricated through selective laser melting (SLM) technique in both vertical and horizontal directions. The microstructure and grain morphology of the as-built sample were studied using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). It was observed that in both vertical and horizontal directions the microstructure of the as-built sample consists of columnar dendrites aligned in the building direction because of the fast-directional cooling presents in the SLM process. However, the microstructural studies revealed that by changing the building direction from vertical to horizontal, both dendritic and grain structures have a tendency to change from columnar to equiaxed. Furthermore, the TEM results showed that different volume fractions of austenite and martensite phases were detected in both directions resulting from complex heat history and wide temperature range during the SLM process.
A-69: Origin and How to Reduce Splatter in Powder Bed Fusion: Hans-Wilfried Mindt1; Mustafa Megahed1; 1Esi Group
Process parameters usually used in powder bed fusion additive manufacturing (PBF) lead to evaporation and a recoil pressure that interacts with powder and molten metal. As a result, splatter particles are ejected from the vicinity of the melt pool. In some cases; especially if the splatter particles are large, the shield gas cannot carry ejected particles out of the processing chamber. They land downstream of shield gas flow on the powder bed leading to process defects due to their mass. Splatter also affects the recyclability of unused powder negatively leading to an overall increase in PBF cost. In this numerical study the origin of splatter is studied by deactivating different terms of the conservation equations. The unprocessed powder is assumed static. Only material ejected from the melt pool is studied. Once the splatter origins are identified, possibilities of reducing splatter by adapting process parameters or alloying elements is explored.
A-70: Performance of Wire-arc Additive Manufactured Ti-6Al-4V and Ti-5Al-5Mo-5V-3Cr Dissimilar Alloy-alloy Composite Interfaces: Jacob Kennedy1; Alec Davis1; Armando Caballero2; Ed Pickering1; Stewart Williams2; Phil Prangnell1; 1University of Manchester; 2Cranfield University
The possibility exists to produce integral components with graded properties by DED Wire-Arc Additive Manufacturing (WAAM). However, critical to a dual material system is to control the interface between the two alloys. In order to explore this capability, trial samples have been produced by depositing Ti64 on Ti5553. The resultant chemical and microstructure gradient and associated interface mechanical behaviour has been investigated. The results show that mixing of Ti5553 alloying elements with the Ti64 primarily occurs in multiple steps, corresponding to the progressive dilution that results from sequential re-melting. This is reflected in the interface microstructure gradient, but is complicated by the associated thermal gradients, which also affect the α phase distribution close to the interface.Compact tensile tests showed that crack fracture paths can also be deflected to follow the interface. The implications for the production of WAAM tailored parts with graded performance are discussed.
A-71: Powder Bed Additive Manufacturing of Cu / 17-4 PH Layered Structures: Alexis Ernst1; Rainer Hebert1; Mark Aindow1; 1University of Connecticut
Powder bed metal additive manufacturing (PBAM) techniques have now reached the point where complex near-net shaped components can be manufactured from powders of a wide variety of alloys. For PBAM, only one material can be used with available equipment for a build. Using a new research PBAM system with a dual-feed hopper, this study examines the additive manufacturing of components with layers of two different materials. Model bilayer samples of 17-4 PH stainless steel and pure copper have been produced using this research AM system. Interfacial microstructures and phases obtained from the PBAM process have been compared with those of 17-4 PH / Cu diffusion couples. This allows purely chemical interactions to be distinguished from the effects of the PBAM process. The use of more than one alloy in PBAM can potentially lead to the manufacturing of complex components with local variations in materials and properties.
A-72: Predicting Phase Morphologies in AM Titanium: Ian Bakst1; 1Honeywell FM&T
Accurately predicting the microstructure and grain morphology of titanium alloys processed through additive manufacturing (AM) techniques presents various difficulties. One such source of difficulty is the formation of martensitic phases (á’, á”, ù, etc.) at the speedy cooling rates inherent to AM processes. The formation of these phases is governed by energetic competition between martensitic and diffusion driving forces. Current thermodynamic databases are limited in their prediction of these phases due to insufficient data for such high cooling rates. Through multi-scale simulation, we improve on the predictions of resulting microstructure of AM titanium. The energy barriers and rates of diffusion-driven and diffusionless phase transformations are computed, as are their relationships to temperature and chemistry. From these rates, we model the evolution of phase morphology in AM titanium. Honeywell Federal Manufacturing & Technologies is operated for the United States Department of Energy under Contract Number DE-NA-0002839.
A-73: Simulation of Part-scale Grain Structure Development During Additive Manufacturing Solidification: Matthew Rolchigo1; Jim Belak1; Benjamin Stump2; Alex Plotkowski2; Robert Carson1; Neil Carlson3; Matt Bement3; 1Lawrence Livermore National Laboratory; 2Oak Ridge National Laboratory; 3Los Alamos National Laboratory
Alloy microstructure development during Additive Manufacturing is complex, occurring on length scales ranging from sub-micron dendrite tips to epitaxial grains spanning many layers of deposited material. A highly parallel cellular automata (CA) code is deployed to investigate grain growth at the scale of parts, using temperature data from high-fidelity fluid and heat transport models of the AM process (OpenFOAM and Truchas) to simulate novel grain structure development with use of complex scan patterns. The microstructure dependence on nucleation parameters, alloy composition, initial conditions, and process parameters will be discussed and compared to experiment, emphasizing texture and the columnar-to-equiaxed transition. The model’s use as a component of the exascale ExaAM project, linking large-scale simulation of process-microstructure-property relationships, is discussed as well. *Work performed under auspices of the U.S. DOE by LLNL under contract DE-AC52-07NA27344, and supported by ECP (17-SC-20-SC), a collaborative effort of U.S. DOE Office of Science and NNSA.
A-74: Synchrotron Imaging of the Influence of TiB2 on Cracking Phenomena During Laser Powder Bed Fusion of Al2139: David Rees1; Chu Lun Alex Leung1; Joe Elambasseril2; Sebastian Marussi1; Saurabh Shah1; Shashidhara Marathe3; Milan Brandt2; Mark Easton2; Peter Lee1; 1UCL Mechanical Engineering; 2RMIT University; 3Diamond Light Source Ltd
The 2XXX series Al-Cu-Mg-Ag alloys are used in aerospace applications for their specific strength and fatigue properties. The alloy is high cost and hence is used low volume specialist components, an ideal application of laser powder bed fusion (LPBF) additive manufacturing. Unfortunately, the alloy exhibits a strong hot cracking susceptibility, often leading to build failure. We investigated two approaches to minimise the formation of hot cracks by controlling the solidification behaviour by: (1) TiB2 inoculant additions; and (2) in situ optimisation of the LPBF process parameters. To understand the underlying cracking phenomena, we first monitored the LPBF of Al2139 with and without the addition of TiB2 using high-speed synchrotron X-ray imaging for a range of parameters. The microstructure (i.e. grain structure and crack morphology) of additive manufactured builds was examined using high-resolution electron microscopy and X-ray tomography. Our results reveal possible methods to reduce crack formation during LPBF of Al2139.
A-75: Tailoring Grain Structures for Metallic Additive Manufacturing: Yijia Gu1; Arezoo Emdadi1; 1Missouri University of Science and Technology
Presently, almost all the alloys used by metallic additive manufacturing (AM) were developed for conventional fabrication. Most of them, especially wrought alloys, are not manufacturable by AM. During AM process, residual stresses due to solidification shrinkage and thermal gradient build up layer by layer, and finally leads to failure (cracking). One way to fundamentally improve the manufacturability of those legacy alloys is grain refinement. In this work, we will use phase-field method to study the grain refinement for AM. The competition between nucleation and growth with the presence of multiple nucleant particles will be simulated. The mechanism of grain refinement under the rapid solidification and the limiting factors, such as nucleant particle size, solute diffusion, and thermal properties of matrix, will be discussed.
Cancelled
A-76: Towards Grain Refinement of Titanium Alloys for Laser Powder-bed Fusion: Marco Simonelli1; Nesma Aboulkhair1; Yau Yau Tse2; Adam Clare1; Richard Hague1; 1University of Nottingham; 2Loughborough University
Most of the traditional alloys present unsuitable microstructures/properties after laser powder bed fusion additive manufacturing due to the extraordinary thermal conditions imposed by these processes. In this study we investigate the effect of iron (Fe) elemental additions to Ti-6Al-4V, the most prevalent titanium alloy in the aerospace industry, to change its solidification path and achieve a fine lamellar grain structure embedded in refined prior-β grains. The study will show how thermodynamic calculations based on the CALPHAD approach were used to guide the alloy selection process. The microstructural evolution of the newly developed alloys is studied using in-situ high energy synchrotron X-Ray diffraction and high-temperature orientation microscopy (EBSD up to 1000 °C): the combined use of these technologies provides insights in the decomposition of the metastable structure formed after L-PBF, the partitioning of the alloying elements during microstructural recovery and the α/β grain morphology evolution.