Additive Manufacturing: Processing Effects on Microstructure and Material Performance: Poster Session
Sponsored by: TMS: Additive Manufacturing Committee
Program Organizers: Eric Lass, University of Tennessee-Knoxville; Joy Gockel, Wright State University; Emma White, DECHEMA Forschungsinstitut; Richard Fonda, Naval Research Laboratory; Monnamme Tlotleng, University of Johannesburg; Jayme Keist, Pennsylvania State University; Hang Yu, Virginia Polytechnic Institute And State University
Monday 5:30 PM
February 24, 2020
Room: Sails Pavilion
Location: San Diego Convention Ctr
A-78 (Digital): Microstructure Control in Microscale Additive Manufacturing of Copper by Localized Electrodeposition: Soheil Daryadel1; Majid Minary2; 1University of Illinois at Urbana-Champaign; 2University of Texas at Dallas
The control of microstructure is one of the most critical challenges facing microscale additive manufacturing (µ-AM) of metals. It is necessary to gain control over the microstructure, and hence mechanical and electrical properties of printed structures for various functional applications. In this presentation, we demonstrate that the microstructure of the microscale 3D-printed metal using the localized pulsed electrodeposition (L-PED) process can be engineered via control over the process parameters. Results show that the density and the orientation of the twin boundaries, and the grain size can be controlled through electrochemical process parameters. Additionally, we employed in situ SEM nanomechanical experiments to directly correlate the microstructure-property relationship. This important advancement eliminates the need for post-processing to engineer the microstructure, which often has undesirable consequences for material properties. The new capability enables control of spatial mechanical and electrical properties of the 3D-printed metal during the process.
A-79 (Digital): The Influence of Porosity and Defects on Fatigue Behavior in Additive Manufactured 316L Stainless Steel Using In-Situ X-Ray Computed Tomography: Aeriel Murphy-Leonard1; David Rowenhorst1; 1Naval Research Laboratory
Three-dimensional techniques such as x-ray micro-computed tomography (XCT) enable the ability to fully visualize and quantify porosity and provide fundamental relationships between pore size and morphology on mechanical behavior and damage evolution. In the current study, the influence of pore and void size, morphology, and distribution on crack initiation, growth, and coalescence during tensile and cyclic loading was examined using XCT on additively manufactured (AM) 316L stainless steel. The samples were produced using laser powder bed fusion techniques where the gauge diameter was 1 mm. Static XCT revealed that in conditions where the cross-sectional area is small majority of the porosity was in-homogeneously distributed where a higher distribution of porosity was found near the surface which is commonly seen in additively manufactured materials.
Cancelled
A-80: β Phase Evolution Process in Selective Laser Melting Titanium-tantalum Continuous Gradient Alloy: Baicheng Zhang1; Xuanhui Qu1; 1USTB
Large scale of titanium-tantalum continuous gradient alloy was built by a self-developed selective laser melting system. The element and phase distribution of gradient alloy were identified by XPS, SEM, EDS and XRD. It can be found that Ti-Ta weight ratio can be successfully controlled to vary linearly. The phase evolution was observed from α→α+β→β corresponding to Ta element increase. The critical Ta content of β phase transition was found at 35% in SLM Ti-Ta system, which is much lower than casting Ti-Ta system (70% of Ta content). The rapid cooling process in SLM lead to the decrease of Ta content as β phase stabilizer. The Young’s modulus obtained by nano-indentation test also verified this phenomenon. The microhardness and corrosion resistance test results were also conducted to characterize the gradient alloy performance.
A-81: 3D X-ray Tomography Analysis of the Effect of Process Parameters on Porosity Formation in Selective Laser Melting of Ti-6Al-4V Parts: Mohamed Goune1; Stephane Gorsse1; Guillaume Aubert1; Sylvie Bordère1; 1Icmcb
The control of properties of manufactured products by Selective Laser Melting (SLM) is made difficult since it depends on many complex interactions between the process parameters, the metallurgical state and the mechanical properties. In that context, built materials of Ti-6Al-4V are often subject to inner defects such as porosity that affect both tensile and fatigue properties. In this work, an original approach based on wise choice of set of process parameters (density E, laser power P, scanning velocity V) and 3D X-Ray tomography analysis is proposed. A theoretical approach is proposed to streamline our results and to provide clarifications regarding the link between process parameters of SLM and porosity formation.
A-82: 3D Printing Ceramics Using Stereolithography: Peter Evans1; Digvijay Yadav1; Brady Butler1; Kelvin Xie1; 1Texas A&M University
Additive manufacturing is an ever-growing field with new techniques being developed as well as a wide assortment of materials becoming accessible. With this has come the ability to fabricate ceramics with various 3D printing techniques. In this study, a commercial, off-the-shelf silica loaded resin will be explored using a low cost commercial stereolithography printer. Through this, a good base line will be created that others developing their own resin can use as a comparison because to our knowledge, none exists. Two sets of samples – square plates and honeycomb cellular structure, were printed. Measurements were taken to quantify the printing resolution limit of this technique. The green bodies were heat treated to different maximum temperatures, and the effect of temperatures on the microstructure and mechanical properties of the honeycomb cellular components were studied.
A-83: Additive Friction Stir-deposition of Copper: Jonathan Priedeman1; Brandon Phillips1; Billy Hornbuckle2; Kristopher Darling2; Paul Allison1; Gregory Thompson1; 1University of Alabama; 2Army Research Lab
Additive friction stir-deposition (AFS-D) is a solid-state, near-net shaping additive manufacturing method process capable of processing a wide variety of metallic systems, including metal-based composites. In this work, AFS-D of copper is explored. A four-pass deposition yielded a fully dense, 3.8 mm thick deposit that was completely bonded to a copper substrate. The high-temperature nature of the processing produced a surface oxide with no further oxidation observed within the interior of the deposit. The influence of AFS-D on the copper’s microstructure is examined, mainly via comparison of feedstock and as-deposited states. The highly textured microstructure of the feedstock was lost in favor of an equiaxed, semi-refined grain structure in the deposit. The mechanical properties of the substrate, interfacial bonding region, and the deposit are explored via micro-hardness mapping.
A-85: Alpha Variant Selection in Additively Manufactured Ti-6Al-4V: Philip Stephenson1; Ryan Demott1; Nima Haghdadi1; Xiaozhou Liao2; Simon Ringer2; Sophie Primig1; 1UNSW Sydney; 2The University of Sydney
Additive manufacturing (AM) is gaining interest in industry. The extreme thermal gradients and cyclic thermal loading involved result in complex and unpredictable microstructures. This is particularly true of Ti-6Al-4V due to its beta-to-alpha solid-state transformation. The preferred selection of certain alpha variants during this transformation has been well documented. This phenomenon significantly influences the mechanical properties and microstructure of titanium alloys and causes the formation of macro-textured regions. However, variant selection has rarely been studied in the context of AM. In this work, Ti-6Al-4V blocks were fabricated using electron beam melting under three different scan strategies to generate different thermal histories. Inter-variant boundary character distributions showed considerable variant selection. Alpha and retained beta crystallographic orientation and prior beta grain boundaries provided evidence of different variant selection mechanisms. Analysis of these features can clarify the competition between modes of variant selection in determining the final microstructure.
A-86: An Investigation into the Recyclability of AlSi10Mg Powder in LENS®: Al Medrano1; Parnian Kiani1; Kaka Ma2; Julie Schoenung1; 1University of California, Irvine; 2Colorado State University
Reusing powders in metal-based additive manufacturing (AM) can help to reduce the production cost and increase the sustainability of the process. Gas atomized AlSi10Mg is frequently used in the AM industry due to the increasing need for parts with complex geometry and high strength. However, it has been not thoroughly investigated whether reusing the powder significantly influences the mechanical behavior of the deposited parts. In this project, blocks were deposited using LENS® with excess powder being collected and reused for five cycles. In order to investigate the effects of reusing powders on microstructure, morphology, and flowability of powder particles, extensive characterization has been done on virgin and reused powder. The blocks have also been characterized to understand the effect of reusing powder on microstructure, density, and mechanical properties. The results from this experiment provide insight into the limits of reusing AlSi10Mg powder in LENS® to build components with competitive properties.
A-87: Annealing of Additively Manufactured Inconel 625: Nakul Ghate1; Amit Pandey2; Amber Shrivastava1; 1Indian Institute of Technology Bombay; 2Ansys Inc.
The objective of this work is to study the effect of heat treatment on Inconel-625 fabricated by using selective laser melting. Annealing is performed to relieve stresses, improve the ductility and toughness of Inconel-625. As-built Inconel-625 samples are annealed at temperatures ranging from 600 ℃ to 1500 ℃. A numerical approach is developed to capture the phase transformation during annealing. The microstructure of the as-built and annealed samples are compared and their hardness is determined experimentally. The as-built microstructure consists of austenite phase without any precipitates. The heat treatment at lower temperatures leads to the formation of orthorhombic Ni3Nb which dissolves at higher temperatures. Meanwhile metal carbide precipitates are observed upon heat treatment at higher temperatures. The heat treatment at low temperatures leads to the formation of intermetallic phases thereby increasing hardness. The intermetallic compounds dissolve at higher temperatures and grain size increases leading to reduced hardness.
A-89: Banded Heat Affected Zone (HAZ) and Post Build Ageing Microstructure Interactions in LBP-DED IN718: Ioannis Bellos1; Ed Pickering1; Chris Heason2; Philip Prangnell1; 1The University of Manchester; 2Rolls-Royce, plc
Banded microstructures arise in Laser Blown Powder Directed Energy Deposition (LBP-DED) manufactured materials associated with re-melting and overlapping of Heat Affected Zones (HAZ) during each deposition pass. In addition, due to limitations imposed by the intended application of many components, full solution treatments cannot always be used. The purpose of this research was to understand the formation of banded microstructures in LBP-DED IN718 samples, in terms of their relationship to the local chemistry and response to subsequent post-build direct ageing treatments. To this end, spatially correlated multi-scale microstructure, compositional, and phase analysis has been performed using EPMA, HR-SEM, and (S)TEM, facilitated by location specific FIB specimens. A complex precipitation sequence was observed across a dendrite as it interacted with a HAZ and responded to ageing, with the precipitate type and morphology being dictated by the original local compositional gradients that existed within the material, as a result of the deposition.
A-90: Characterization and Integration of the Anisotropy of Additively Manufactured Titanium in the Topology Optimization of Light-weight Structures: Matthew Vaughn1; Justin Unger1; Alberto Torres1; Andrew Gaynor2; Brandon McWilliams2; James Guest1; Kevin Hemker1; 1Johns Hopkins University; 2US Army Research Laboratory
Additive manufacturing (AM) creates an opportunity to produce geometries that were previously unachievable through conventional manufacturing techniques; although the relation between processing and part performance is not fully understood. Titanium alloys are desirable candidates for AM, but the Selective Laser Melt (SLM) process by which titanium alloys are typically additively manufactured consistently produces parts with anisotropic and location-specific tensile properties. Topology Optimization (TO) is an ideal complement to AM as it generates highly efficient designs that take advantage of AM’s ability to realize complex topologies. However, TO models typically assume homogeneous isotropic properties and thus need to be adapted to the AM process. This talk outlines the development and use of shear, compression and tensile tests that provide an understanding of the yield surface and stiffness anisotropy of AM Ti-6Al-4V. Through the investigation a tension-compression asymmetry was elucidated as well as a variance between in build plane and build direction properties. The location and size dependence of microstructure and strength will be discussed, as will efforts to integrate experimental and TO efforts.
A-91: Controlling Microstructural Evolution in Metal Additive Manufacturing Using Bessel Beams: Thej Tumkur1; Sheldon Wu1; Tien Roehling1; John Roehling1; Saad Khairallah1; Sullivan Figurskey1; Devon Courtwright1; Michael Crumb1; Manyalibo Matthews1; 1Lawrence Livermore National Laboratory
We report on the generation of non-conventional Bessel beams and their efficacy in enabling advanced microstructural control in laser-based metal additive manufacturing. Bessel beams have been utilized for high-resolution microscopy and precision laser machining, owing to their extended depth of focus compared to traditional beam shapes. In our studies, the effect of a larger depth of focus in Bessel beams (compared to Gaussian beams) was evident from the morphology and microstructures of single tracks produced by laser powder bed fusion of stainless steel powders. We will discuss the significance of our experiments, supported by modeling, in relation to the degree of tolerance for positioning of the focal plane, and for achieving greater control over thermal and microstructural evolution of melt pool profiles during selective laser melting. Prepared by LLNL under Contract DE-AC52-07NA27344, supported by the Office of Laboratory Directed Research and Development (LDRD), tracking number 18-SI-003.
A-92: Creep Deformation Study of Heat-treated Nickel Alloy 718: Alejandro Hinojos1; Hyeyun Song2; Alber Sadek2; Wei Zhang1; Michael Mills1; 1The Ohio State University; 2The Edison Welding Institute
Additive manufacturing (AM) has rapidly become integrated in the aerospace sector over the past decade. Research thrusts in the past have focused on suppressing the unorthodox microstructures through process parameter control. However, it is not yet understood whether these unique microstructures could be exploited as precursor templates to enhance the creep properties of alloys in high temperature applications. In this study, Inconel 718 (IN718) was fabricated through selective laser melting (SLM) for the analysis of single step aging heat treatments at 720 and 680°C for 10 hours. Monotonic compression creep tests were performed at 649°C and 700MPa. Preliminary testing has shown that the single step heat-treated condition had substantially better creep rates and strain than the conventionally processed alloy. Ensuing scanning electron microscopy and transmission electron microscopy was performed to evaluate the role of the AM microstructures in creep deformation in the as-fabricated and heat-treated conditions.
A-93: Critical Quenching Rates After Solution Annealing: Peculiarities of Aluminum-silicon Alloys Fabricated by Laser Powder-Bed Fusion: Stephan Hafenstein1; Leonhard Hitzler1; Enes Sert2; Andreas Öchsner2; Markus Merkel3; Ewald Werner1; Jonas Von Kobylinski1; 1Technical University Munich; 2Esslingen University of Applied Sciences; 3Aalen University of Applied Sciences
The microstructural characteristics of selective laser melted aluminium-silicon alloys differ vastly from their respective cast counterparts. The high cooling rates lead to an increased (non-equilibrium) solubility of Si in α-Al and consolidates in a cellular structure starting from the melt pool boundaries. Correspondingly, the Si-content is inhomogeneous across a single scan track, with the Si-content decreasing from the scan track boundaries towards its center. Si-segregations occur in these oversaturated regions and this enrichment is further escalated in remolten areas. When left untreated, these Si-enrichments represent brittle areas and predetermined locations of fracture. Efforts to overcome these segregations by means of post-heat-treatments, including a solution annealing step, were successful to dissolve the segregations, but at the cost of lowering the mechanical strength. Interestingly, the quenching rate of SLMed AlSi after solution annealing seemed to impact the effectiveness of the subsequent artificial aging, which is unknown for cast AlSi.
A-94: Dendrite Orientation Transition in Laser Remelted Titanium Alloys: Phase Field Simulation and Experiment Validation: Yujian Wang1; Yu Zou1; 1University of Toronto
Microstructure evolution of titanium alloys during laser-based additive manufacturing process plays a significant role in their final mechanical properties. In this study, we have developed a three-dimensional heat transfer model and a microscale phase field model to illustrate the dendritic growth behaviour during laser remelting process. We find that a large thermal gradient and cooling rate in a local molten pool result in dendrite orientation transition (DOT) – the dendrite arm angle changes from 90° to 45°. We used a 2 W laser to remelt two titanium alloys (Ti-5Al-5Mo-5V-1Cr-1Fe and Ti-6Al-4V) for 2-3 seconds. The grain morphologies after remelting is dependent of laser processing parameters and materials. The simulation results agree well with the experimental observation.
A-95: Direct Laser Metal Deposition of René 108 Single Crystal: Praveen Sreeramagiri1; Ajay Bhagavatam1; Husam Alrehaili1; Guru Dinda1; 1Wayne State Unievrsity
Single crystal Ni-based superalloys are currently the materials of choice for the hottest and most severely stressed parts in gas turbines and aero engines. This paper reports a processing strategy of direct laser metal deposition of René 108 single crystal by effectively controlling the process parameters and cooling rate. The as-deposited specimen exhibited a single grain throughout the volume with the <100> growth direction. Microstructural investigation of the as-deposited sample revealed the presence of spherical γ' with an average size of 46 nm in the dendrite core and eutectic phases of γ/γ'/MC along the inter-dendritic boundaries. Heat treatment of the sample revealed a trimodal distribution of γ' precipitates with an average size of 271 nm cuboidal, 58 nm spherical γ', and rafted γ'. XRD investigation of the heat-treated sample revealed a shift in lattice parameter from 358 pm to 351 pm as a result of rafting and strain relief.
A-96: Effect of Partitioning Treatment on the Mechanical Behavior of an Additively Manufactured Ti-6Al-4V Alloy: Kenta Yamanaka1; Manami Mori2; Yusuke Onuki3; Shigeo Sato3; Akihiko Chiba1; 1Tohoku University; 2National Institute of Technology, Sendai College; 3Ibaraki University
The quenching and partitioning (Q&P) process, which involves annealing of martensite to produce a large amount of fine austenite, has been developed for multiphase steels with excellent mechanical properties. Here, we applied this concept to additively manufactured Ti-6Al-4V alloys that had experienced a martensitic transformation during the process. Specimens prepared by electron beam melting and were annealed below the ß-transus to partition the alloying elements. The hardness of the as-built specimens decreased significantly at the initial stage of annealing, indicating the influence of dislocations in the as-built state. Interestingly, the annealed materials showed a decreased 0.2% proof stress while showing higher work hardening upon tensile loading. Such a deformation behavior is quite different from that generally observed in Ti-6Al-4V alloys and may be derived from the transformation-induced plasticity. The martensitic transformation kinetics and dislocation dynamics of the materials under tensile loading were examined by in-situ neutron diffraction measurements.
A-97: Effect of Scanning Strategy on Additively Manufactured Ti6Al4V: Nakul Ghate1; Bhanupratap Gaur1; Amber Shrivastava1; 1Indian Institute of Technology Bombay
This study investigates the influence of different scanning strategies on the hardness of the parts, fabricated by Direct Metal Laser Melting. In this work, pre-alloyed powder of titanium alloy (Ti-6Al-4V) is used to produce dense parts with three different scanning strategies: unidirectional, alternate and cross-hatching. A numerical scheme is developed to predict the heat transfer, fluid flow and thermal history-based phase transformation during the process. Surface hardness is calculated from the obtained phase fractions. Hardness is measured experimentally and X-ray diffraction is used for phase identification. The hardness is found to be highly dependent on the microstructure of as-built parts. The results show that rapid solidification during Direct Metal Laser Melting leads to the formation of hcp structured acicular martensite from the parent beta phase, which increases the hardness. Higher part densities are observed for cross-hatching strategy compared to other scanning strategies. The trends of experimental and predicted hardness against scanning strategies compare well.
A-98: Effect of Semi-solid Treatment on Microstructure and Mechanical Properties Additive Manufactured Inconel 625: Lukasz Rogal1; Damian Kalita1; Karol Janusz1; Jan Dutkiewicz1; Marek Węglowski1; Tomasz Durejko2; Anna Antolak-Dudka3; 1Institute of Metallurgy and Materials Science; 2Military University of Technology ; 3Military University of Technology
Two various methods of rapid manufacturing, Electron Beam Additive Manufacturing (EBAM) and Laser Engineered Net Shaping (LENS), were used in order to fabricate 625 Inconel elements. To improve its properties, a semi-solid treatment has been developed. It consisted of rapid quenching from the mushy zone, corresponding to 20-60% of the liquid fraction, to obtain a supersaturated solid solution by alloying elements. The DSC allowed to determine the semi-solid range of elements after 3D printing from wire and powder. Next, the samples were heated up to 1345°C and 1380°C, which corresponds to 50 % of the liquid fraction, held for 15 min, and next water quenched. The LENS treated sample exhibited γ-dendritic cells with short secondary arms and interdendritic areas enriched in the alloying elements. In the samples obtained by the EBAM proces, the microstructure consisted of coarse γ-re-melted dendrites (which started to spheroidise) between which a rapidly quenched secondary phase was present in the volume of 45%, enriched in the intermetallic phases (carbides, Laves phase). Additionally, aging at 650˚C revealed significant increases in hardness for the samples obtained by the EBAM process. Acknowledgment: The research was supported by the project No 2016/23/B/ST8/00754
A-99: Effect of Temperature Dependent Properties on the Accuracy of Physics-based Surrogate Models for Powder Bed Fusion Additive Manufacturing: Alexander Wolfer1; Richard Otis2; Brian Weston3; Saad Khairallah3; Andy Anderson3; Andrew Shapiro2; Jean-Pierre Delplanque1; 1University of California, Davis; 2Jet Propulsion Laboratory, California Institute of Technology; 3Lawrence Livermore National Laboratory
Low-order or surrogate models are often used to efficiently investigate various processing strategies for powder bed fusion processes, as well as to perform sensitivity analysis or uncertainty quantification. A common simplification used in many physics-based lower order models is to assume constant thermophysical properties, ignoring any temperature dependence. It is possible to capture such temperature dependency with high-fidelity simulations but at a prohibitive computational for applications that require a large number of cases to be considered (e.g. uncertainty quantification). An investigation into several approaches to account for the temperature dependence of thermophysical properties in a surrogate model is presented. We discuss the advantages and disadvantages of various modeling assumptions and how they affect the accuracy of the predictions (e.g. melt pool geometry or thermal gradients). Comparisons are made with high-fidelity simulations that include temperature dependent thermal properties as well as additional physics, such as phase change and melt-pool fluid dynamics.
A-100: Effect of Thermal History on Elastic Strain and Microstructural Evolution in Additive Manufacturing: Kathryn Small1; Michael Groeber2; Mitra Taheri1; 1Johns Hopkins University; 2Ohio State University
Direct metal laser sintering (DMLS) is a thermally complex fabrication process which induces anisotropic microstructures in final components. The prediction of material properties in additively manufactured parts is difficult due to our lack of understanding of the microstructural evolution during additive processes. Mechanisms of the evolution may be observed using GND density and elastic strain characterization with accompanying thermal history data; however, the remelting and heat affected zone present during the laser tracking process makes thermal modelling of the DMLS process difficult. A single-track sample is used to simplify the thermal model of the DMLS part being analyzed in this study, enabling connection between microstructural features analyzed by electron backscatter diffraction (EBSD) and the thermal history of Inconel 625 fabricated by DMLS. Elastic strain concentrations and dislocation structures are observed throughout the length of the sample, allowing observation of rapid solidification present during a single laser track during DMLS.
A-101: Effects of Laser-energy Density and Build Orientation on the Defect Structure, Microstructure and Tensile Properties of Laser Powder Bed Fused Inconel 718: Dillon Watring1; Jake Benzing2; Nik Hrabe2; Ashley Spear1; 1University of Utah; 2National Institute of Standards and Technology (NIST)
This study investigates the processing-structure-property relationships for Inconel 718 (IN718) manufactured by laser powder bed fusion. Specifically, the influence of build orientation and laser-energy density on the defect structure, microstructure, and tensile properties was investigated. Three different combinations of build orientation and laser-energy density were selected for the IN718 specimens: 0° and 38 J/mm3, 0° and 62 J/mm3, and 60° and 62 J/mm3. In depth characterization of the three build conditions was performed using X-ray computed tomography, electron backscatter diffraction, backscattered electron imaging, and secondary electron imaging. A total of 32 mini-tensile specimens (gauge length of 3 mm) were tested to investigate the mechanical properties of the three build conditions. In the absence of as-built surface roughness, laser-energy density had a large effect on the mechanical properties and build orientation had very little effect . It was found that the defect structure dominates the mechanical properties with non-optimized laser-energy density.
Cancelled
A-102: Effects of Nano-scale TiC on Defects and Mechanical Properties of IN738LC Manufactured by Selective Laser Melting: Zhengrong Yu1; Xiaogang Hu1; Qiang Zhu1; Hui Ding2; 1Southern University of Science and Technology; 2Southeast University
Effects of nano-scale TiC with contents of 0.1%，0.3%，1.0% and 3.0% on defects and mechanical properties of the high thermal cracking sensitivity superalloy IN738LC manufactured by selective laser melting (SLM) process were studied. Addition of the nano-scale TiC inhibits cracking behavior of the SLMed IN738LC. IN738LC parts with cracking free and low porosity were obtained in a wide range of process parameters.The studies showed that original cracks were transformed into discontinuous micro pores, and thus tensile properties at room temperature and 700℃ were improved. Mechanics of the effects is discussed in this paper.
A-103: Effects of Process Parameters on Microstructure and Mechanical Properties of Wire Arc Additive Manufactured Al-Mg-Si Alloy: Gautier Doumenc1; David Gloaguen1; Bruno Courant2; Pascal Paillard3; Laurent Couturier3; Alexandre Benoit4; 1IRT-GeM-IMN; 2GeM - Research Institute in Civil and Mechanical Engineering; 3IMN - Nantes Materials Institute; 4IRT Jules Verne - French Institute in Research and Technology in Advanced Manufacturing
Wire and Arc Additive Manufacturing (WAAM) offers a high deposition rate leading to the capability to manufacture large components with lower cost. Age hardened aluminium alloys are widely used for structural applications because of their high specific properties. Recent development of a Metal Inert Gas deposition process based on a low-energy short-circuit transfer mode, called Cold Metal Transfer //174; made the use of these poorly weldable alloys, such as age hardened 6061 aluminium alloy, possible by WAAM. Microstructures and nanostructures are strongly influenced by the main process parameters and do have a critical influence on the mechanical performances of the built part. To date, no detailed studies on the precipitation hardening in aluminium parts achieved by WAAM are available, especially as regard to Al-Mg-Si alloys. Therefore, the present work aims to relate the relationship between microstructural features and mechanical properties in such a WAAM additively manufactured alloy.
A-104: Effects of the Energy Density and Building Angle on the Tensile Properties of SLM Ti-6Al-4V Alloys: Jungsub Lee1; Woojin An1; Imdoo Jung2; Jusik Kim3; Sangshik Kim1; Hyokyung Sung1; 1Gyeongsang National University; 23D Printing Center, Korea Institute of Materials Science; 3ANH structure
Effects of the process parameters on the microstructure and tensile properties of SLM Ti-6Al-4V alloys were investigated. We had control the laser power and scan speed to control the energy density (93, 103 and 112 W). In H and L specimen, two different heights of 30 and 10 mm were employed. Lamellar colony microstructures were formed due to solidification from β transus temperature. Lamellar thickness increased with increasing energy density. Yield and tensile strengths were about 800~850 MPa and 950~1000 MPa, but the elongation of L specimens were somewhat higher (2~3%) due to fast heat release rate. In the effect of building angle (0°, 45° and 90°), the elongation was the highest in 90° specimen due to its smooth surface. In the surface GOS value was lower due to fast cooling rate affected by high surface roughness, and brittle fracture was evident which deteriorates the tensile elongation.
A-105: Evolution of Dislocation Cell Substructure and its Effect on Precipitation Behavior in AM-IN718: Thomas Gallmeyer1; Jack Dale1; Behnam Aminahmadi1; Aaron Stebner1; 1Colorado School Of Mines
Laser powder-bed fusion (L-PBF) processes induce rapid solidification and thermal cycling that give rise to hierarchical microstructures and anisotropic mechanical properties across an array of materials, IN718 included. One interesting aspect of the as-printed AM microstructures is the formation of a dislocation cell substructure that has been shown in influence strength and ductility in mechanical responses. As a precipitation strengthened alloy, determination of the effects of the dislocation cell substructure found in additively manufactured IN718 on microstructural evolution is crucial for understanding post-processing conditions for additively manufactured IN718. We present an investigation characterizing the nature of these dislocation cell substructures, their evolution as the result of heat treatment, and their influence on the subsequent nanoprecipitation using advanced TEM techniques.
A-106: Experimental Study on the Laser Cladding of T15 Coating for 42CrMo Steel: Yingtao Zhang1; Meng Jiang1; Gang Wang1; Xiulin Ji1; 1College of Mechanical & Electrical Engineering, Hohai University
42CrMo steel is a kind of medium carbon allof steel mainly used for manufacturing heavy duty transmission parts. Laser cladding is an advanced surface technology, and it can be applied to improve wear and fatigue resistance properties by getting a high surface hardness. In this paper, pulse laser cladding experiments were conducted on 42CrMo surface with the powder of T15 high speed steel. The microstruture and of cladding layer were observed by optical microscopy (OM) and scanning electron microscopy (SEM). The hardness gradient of section was tested. The hardness of surface and substrate is 747 HV and 195 HV. After friction and wear testing, the average dry friction coefficient is 0.448 and the volume loss is 689100 µm3.
A-107: Fabrication of γ/γ’-strengthened Co-Al-W Alloys by Direct Laser Deposition: Pyuck-Pa Choi1; Boryung Yoo1; 1KAIST
Co-Al-W-based alloys strengthened by a two-phase γ/γ’-microstructure have been researched for more than a decade due to their excellent high-temperature properties, such as creep and hot corrosion resistance. However, until now research on these promising alloys have mostly focused on samples fabricated by conventional casting processes and only very little is known about the structure-property relationships of additively manufactured parts. Here we report on γ/γ’-strengthened Co-Al-W alloys fabricated using the direct laser deposition (DLD) process. Careful control of the DLD parameters yielded thin-walled samples of more than 15 mm in height without the occurrence of hot-cracking. Upon increasing the laser power, we could observe the formation of γ’-precipitates in as-built samples. As-built and post heat-treated samples were characterized on various length scales, using X-ray diffraction, electron microscopy, and atom probe tomography, in order to further to elucidate the relationship between the microstructure and the high-temperature properties.
A-108: Gamma-titanium Intermetallic Alloy Produced by Selective Laser Melting Using Mechanically Alloyed and Plasma Spheroidized Powders: Igor Polozov1; Vera Popovich2; Nikolay Razumov1; Tagir Makhmutov1; Anatoliy Popovich1; 1Peter the Great St. Petersburg Polytechnic University; 2Delft University of Technology
Conventional manufacturing of titanium intermetallic alloys is associated with brittleness, hard machinability and, consequently, the high cost, which makes additive manufacturing a promising way of producing complex intermetallic parts. At the same time, γ-TiAl alloys exhibit good high temperature strength, fatigue and oxidation resistance. In the present study the gamma-based alloy spherical powders were prepared by mechanical alloying from elemental powders followed by the plasma spheroidization process. Microstructure and phase composition of the produced powders were studied after different milling times in a planetary mill. The optimally milled powders were treated in the flow of a thermal plasma to obtain powder particles with a high degree of sphericity. The produced spherical powders were used in Selective Laser Melting (SLM) process with high preheating temperatures to obtain crack-free intermetallic samples. The microstructure and phase composition of the SLM-ed TiAl-samples were investigated with regard to different process parameters.
A-109: Heat Treatment of Wire+Arc Additively Manufactured Bimetallic Structures: Rumman Ahsan1; Jae-Deuk Kim2; Gi-Jeong Seo1; Changwook Ji2; P. K. Liaw3; Duck Bong Kim1; A. N. M. Tanvir1; 1Tennessee Technological University; 2Korea Institute of Industrial Technology; 3The University of Tennessee, Knoxville
The wire+arc additive manufacturing process is fitted to fabricate bimetallic additively manufactured structures (BAMS) and have a combination of complementary properties in a single component. The BAMS often have different properties compared to the wrought parent materials, hence, heat treatment might require to attain desired properties. In this work, BAMS of low carbon steel and austenitic stainless steel was heat-treated with varied heat treatment conditions to improve the mechanical integrity of the part. Changes in the microstructure, strength, elongation, and failure location along with compositional gradient and hardness were observed followed by the heat treatment of the BAMS. The microstructure and elemental composition were characterized to justify the change in mechanical properties and the failure location of the BAMS. Based on the results, this study justifies the heat treatment of BAMS and suggests the optimum heat treatment conditions for the mentioned BAMS.
A-110: Influence of Print Orientation on Microstructure and Mechanical Performance of Selective Laser Sintered Polyamide-12: Anil Krishna Battu1; Tamas Varga1; Josef Christ1; Zachary Kennedy1; Wenbin Kuang1; Christopher Barrett1; 1Pacific Northwest National Laboratory
Additive manufacturing (AM) has been developed extensively in recent years to create variety of complex structures. Understanding the relationships between processing conditions and the resulting microstructure is critical for property evaluation of end components and optimization of the manufacturing process. SLS is one of the fastest growing AM techniques. In this work, we investigated the influence of processing conditions on the internal microstructure and mechanical properties of polyamide-12 parts. Using XCT to characterize the internal microstructure (porosity) of samples of four different build orientations we studied the relationships between SLS processing conditions, microstructure and mechanical properties. In this presentation, how manufacturing process affected pore volume, size, and pore connectivity in SLS specimens and how the evolved microstructure, in turn, affected product performance. The performance was characterized by tensile testing and analysis of the viscoelastic behavior of the specimens. Results from aging studies performed under varying conditions will also be presented.
A-111: Influence of the Partial Pressure on the 316L Stainless Steel fusion with the Selective Laser Melting Process: Alicia Annovazzi1; Nouredine Fenineche2; Benjamin Vayre3; 1LERMPS-UTBM-AddUp; 2LERMPS-UTBM; 3AddUp
The Selective Laser Melting process is an additive manufacturing process based on superposition of melted metal powder layers by a LASER beam. Consequently, under such thermal conditions, oxidations can quickly occurr. To avoid the contamination of the metallic powder during the melting, the process is carried in a sealed enclosure with an inert atmosphere. Thus, fusion conditions can be modified, in particularly the partial pressure. The objective of the work is to determine the fusion state difference between experiments at atmospheric pressure with argon, and in the case of low pressure (rough vacuum). Experiments have been made with 316L Stainless Steel with the aim of: realizing tracks and parts in different pressure conditions and fusion parameters; understanding the physical phenomena which impact the laser-matter interaction, influence the particles ejections and change the fusion morphology. To do so, Scanning Electron Microscopy and rapid camera have been used to highlight the evolution.
A-112: Influence of the Process Parameters on the Densification and Microstructure of Ni-based Superalloys with Different Amount of γ Former Alloying Elements Processed by Laser Powder Bed Fusion: Giulio Marchese1; Simone Parizia1; Antonio Sivo1; Emilio Bassini1; Flaviana Calignano2; Sara Biamino1; Daniele Ugues1; 1Department of Applied Science and Technology, Politecnico di Torino; 2Department of Management and Production Engineering, Politecnico di Torino
Ni-based superalloys are characterized by high-temperature strength, oxidation and corrosion resistance making them excellent for several applications such as aerospace and chemical sectors. Additive manufacturing (AM) processes allow the fabrication of complex parts in a single step resulting attractive for Ni-based superalloys. Among the AM processes, laser powder bed fusion (LPBF) has been extensively used for the production of these alloys. However, it is crucial to select the appropriate process parameters to obtain high densification level particularly when the amount of gamma prime (γ′) former alloying elements is increased since this affects weldability. This work investigates the effect of different process parameters on the densification and microstructure of various Ni-based superalloys characterized by increasing amounts of γ′ former alloying elements, studying the balance between pores and cracks reduction and the resulting microstructure. The possibility to form superalloys with increasing concentration of γ′ phases can highly enhance their mechanical properties.
A-113: Investigation of Martensite α’ Phase Transformation during Heat Treatment of High Speed Selective Laser Melted Ti6Al4V Components: Paul Lekoadi1; Nthabiseng Maledi2; Monnamme Tlotleng1; Bathusile Masina1; 1CSIR; 2University of Witwatersrand
This study presents the investigation of heat treatment on microstructural and hardness properties of Ti6Al4V components produced by high speed selective laser melted (SLM). The heat treatments were performed in order to improve and homogenize the Ti6Al4V microstructure which influence the resultant hardness value. It was found that sub-transus temperatures of 700°C and 950°C does not completely transform the martensite α’ phase but results in a slight decrease in hardness. Heat treatment at 1000°C for 8 hours followed by furnace cooling transformed the martensitic α’ phase into lamella α+β microstructure, with a decrease in hardness. Furthermore, the relationship of hardness as a function of residence time was developed.
A-114: Investigation of the Effect of Beam Scan Strategies on the Microstructure of EBM Additively Manufactured Inconel 738 Builds: Chris Blackwell1; Meiyue Shao1; Sriram Vijayan1; Sabina Kumar2; Sudarsanam Babu3; Joerg Jinschek1; 1Ohio State University; 2University of Tennessee; 3Oak Ridge National Laboratory
Additive manufacturing (AM) offers fast, customizable, near-net production of metallic parts, especially when sophisticated part geometries are required. However, the microstructures of these AM parts often vary from those produced by traditional manufacturing. During the AM build process, materials experience complex, cyclic thermal gradients that lead to microstructural inhomogeneities. More empirical data is needed for different alloy/AM method combinations. Here we characterize effects of electron-beam melting powder-bed fusion (EBM-PBF) on Inconel 738 (IN738) microstructures. In Inconels, previous studies have shown that precipitate locations and morphologies are dependent on cooling rates, while similar studies looking at titanium alloys have shown that matrix phase grain sizes and morphologies vary with electron beam scanning parameters. Three different IN738 samples, built under different electron beam scanning strategies, are analyzed using SEM. Precipitate phase densities, compositions, and morphologies; gamma grain sizes and orientations; as well as microhardness are quantified with statistical significance.
A-115: Investigation of the Effect of Process Parameters on the Microstructural Evolution and Mechanical Properties of Inconel 718 Additively Manufactured in Direct Metal Laser Melting (DMLM) Process: Nicholas Barta1; Satya Ganti1; Navin Sakthivel1; Jim Overstreet1; Anjani Achanta1; Chad Yates1; Joshua Snitkoff1; Thomas Dobrowolski1; 1Baker Hughes, a GE Company
In the recent years, additive manufacturing has manifested itself as an unparalleled fabrication technique for Inconel 718 parts employed in aerospace, process, oil and gas industries etc. The rapid solidification and the repeated heat incidence during the DMLM process significantly affects renders drastic properties changes. Literature delineates a vivid gap in the efforts to capture the coherent relationship between process parameters and material performance characteristics in a production environment. The current research is an endeavor to cement the gap by studying the effect of process parameters-laser power, laser scan speed, hatch spacing, layer thickness on the, tensile strength and fracture toughness. The goal is to optimize the material performance under the conditions of improved production rate parameters such as layer thickness and laser scan speed. The research will present the trends of the process – structure – property- performance relationships and optimal parameters for processing in a production environment.
Cancelled
A-116: Joint Characteristics of Additively Manufactured 316L Stainless Steel Using Vacuum Brazing: Gidong Kim1; Dong-jin Oh1; Yongjoon Kang1; So-young Park1; Sang-woo Song1; 1Korea Institute of Materials Science
Additively manufactured (AM) 316L stainless steel using laser-powder-bed-fusion (L-PBF) technique generally shows superior strength and ductility due to its fine microstructure. However, there are some limitations originated from small substrate size of L-PBF machine and difficulty with removing inner supports. Therefore, some parts are required for a successive joining process such as brazing to make complete configuration. Thus, reliable joint properties should be secured for AM materials to ensure the integrity. Vacuum brazing exhibits several benefits such as clean surface, low residual stress and low distortion owing to uniform heating and cooling. In this study, joint properties for both AM and wrought 316L using the vacuum brazing with Ni-based insert alloy were evaluated. The specimens were prepared followed by AWS C3.2M:2008. Shear test for a single lab joint and microstructure examination were conducted.
A-117: Laser Powder Bed Fusion Parametric Investigation of Binary Al-Si Alloys: Holden Hyer1; Le Zhou1; Joshua Haupt1; Sharon Park1; Brandon McWilliams2; Kyu Cho2; Yongho Sohn1; 1University of Central Florida; 2US Army Research Laboratory
The near-eutectic Al-Si alloys such as AlSi10Mg or Al12Si have been widely adopted for laser powder bed fusion (LPBF), because they can be built without excessive pores, and more importantly, without solidification cracking. To explore the composition-dependent buildability, six Al-Si alloy powders, 0.5, 1.0, 2.0, 6.0, 12.6, and 16.0 wt.% Si were produced by gas atomization. Then, 12x12x12 mm cube samples of each composition were produced by LPBF as a function of scan speed at laser powers of 250W and 350W. Regardless of LPBF parameters employed, solidification cracks were observed for the 2 wt.% Si alloy with the highest freezing range near the solubility limit. Minor flaws, mainly due to lack of fusion, were observed for 0.5 and 1.0 wt.% Si alloys with higher liquidus temperature. Sub-grain cellular Al-Si structure was observed for all alloys, and the cellular boundary was observed to be thicker for alloys with higher Si content.
A-118: Lattice Manufacturability Using Electron Beam Powder Bed Fusion: Paul Korinko1; Dale Hitchcock1; John Bobbitt1; Spencer Scott1; 1Savannah River National Laboratory
SRNL is working with other national laboratories and sites to evaluate the manufacturability of the Electron Beam Powder Bed Fusion Process. A variety of lattice types have been printed and the ease of cleaning is being investigated. The desired lattice size is a 4 mm octet truss configuration. This lattice has been printed and challenges with cleaning it have been realized. The initial results have led to modifying the cell size to determine the scale at which the cells can be easily cleaned out. A method has been developed but challenges remain. This presentation will describe the printing process used, design of the cells, the results of the cleaning efforts, and the quasi-static property testing results.
A-119: Localized Plastic Deformation in Thin-walled Selective Laser Melted IN718 Specimens: Sara Messina1; Chris Torbet1; Chase Joslin2; Michael Kirka2; Matthew Begley1; Tresa Pollock1; 1University of California, Santa Barbara; 2Oak Ridge National Laboratory
Additive manufacturing of structural alloys affords the opportunity to design components with complex geometries. To date, studies demonstrate the ability to additively manufacture and heat treat large components, from which test specimens can be cut and shown to possess nominal or near-nominal material properties. Because scan patterns are geometrically-dependent, solidification is less controllable for small parts where the critical dimension approaches the layer thickness. For gamma"-strengthened IN718, solidification critically affects the microstructure, which governs the mechanical properties. This study examines thin-walled selective laser melted IN718 specimens to determine the influence of microstructural and skin effects, build plate position, and build orientation on the mechanical performance of components on the order of 1 mm. It employs tensile testing with digital image correlation to reveal localized deformation, EBSD for texture information, and resonant ultrasound spectroscopy to quantify residual stress not dissipated in post-build HIP and STA treatments.
A-120: Machine Learning Approach for Process Optimization of Pure Cu in a Powder Bed Fusion Additive Manufacturing with Electron Beam: Kenta Aoyagi1; Tadashi Kii2; Nobuyuki Sasaki2; Hirofumi Watanabe3; Yoshitaka Shibuya3; Kenji Sato3; Akihiko Chiba1; 1Institute for Materials Research, Tohoku University; 2Japan Additive Manufacturing & Processing Technology (JAMPT) Corporation; 3JX Nippon Mining & Metals Corporation
Additively manufactured pure Cu parts have attracted much attention because Cu has a high thermal conductivity and additive manufacturing can provide complex-shaped parts, enabling a high-efficient heat radiator. However, it is difficult to obtain additively manufactured pure Cu parts with high density because a process window for pure Cu is narrow. Absorptivity of Cu for electron beam is higher than that for laser, and then, electron beam melting (EBM), one of a powder bed fusion additive manufacturing with electron beam, allows pure Cu parts with higher density than selective laser melting. In this study, therefore, we optimized process condition by a machine learning approach in order to determine a robust process condition, and evaluate density, microstructure, and physical properties of pure-Cu parts fabricated under a predicted condition. In addition, cuboid blocks with flow channels were also fabricated under the predicted condition.
A-121: Mechanical Properties of AlSi10Mg Processed by Laser Powder Bed Fusion at Elevated Temperature: Even Hovig1; Amin Azar2; Mohammed Mhamdi2; Knut Sørby1; 1Norwegian University of Science and Technology; 2SINTEF Industry
AlSi10Mg processed by laser powder bed fusion is expected to have remarkable mechanical properties due to its cellular microstructure. However, the as-processed material is often both anisotropic and contains significant residual stresses. To mitigate these problems, a retrofitted heating system was used to elevate the process temperature to 200°C. The results show low levels of porosity, anisotropy and residual stress. Furthermore, the effect of three heat treatment conditions (as-built, stress relief, and T6) on the tensile properties were investigated. For this purpose, 14 tensile samples were built in seven different orientations. Digital image correlation was used to understand the deformation mechanism for each heat treatment condition. The results show that the as-built material have comparable properties to the stress relieved condition, while T6 heat treatment resulted in slightly increased ductility. Based on the results, processing AlSi10Mg at elevated temperature can eliminate the need for post-build stress relief heat treatment.
A-122: Mechanical, Thermal and Corrosion Properties of Cu-10Sn Alloy Prepared by Selective Laser Melting: Congyuan Zeng1; Bin Zhang1; Ali Hemmasian Ettefagh1; Hao Wen1; Hong Yao1; Wenjin Meng1; Jonathan Raush2; Shengmin Guo1; 1Louisiana State University; 2University of Louisiana at Lafayette
To obtain a better knowledge of Cu-10Sn (wt. %) alloy fabricated by selective laser melting (SLM), specimens with different orientations were prepared and then vacuum annealed at 600℃ and 800℃. The composition, microstructures, mechanical, thermal and corrosion properties were investigated for both as-fabricated (AF) and as-annealed (AA) specimens. The AF specimens exhibit the smallest grain size and the highest compression strength compared with AA specimens, which is consistent with Hall-Petch equation. Thermal conductivity (TC) of the AF specimens is ~ 10% and over 20% higher than that of AA specimens annealed at 800℃ and 600℃, respectively, which can be ascribed to the two-phase constituents, lower porosity and nano-sized pores of the AF specimens. The corrosion rate of AF specimens is almost two times higher than AA specimens due to the different morphology of passive layer, intergranular corrosion and internal galvanic corrosion.
A-123: Microstructural Characteristics of Stainless Steel 316L Processed by Selective Laser Melting Technology: Ismat Ara1; X. W. Tangpong1; Fardad Azarmi1; 1North Dakota State University (NDSU)
Among various additive manufacturing methods, selective laser melting (SLM) is a practical method for metal manufacturing due to its ability to make complex geometry and fabricate parts with superior mechanical properties. Utilization of high strength laser in SLM system forms a high temperature gradient which may alter microstructure of 3D printed metals due to rapid cooling during solidification process. The present study focuses on the microstructural evolution of AISI 316L stainless steel manufactured by SLM to better understand its characteristics and features for further improvement of this technology. Optical Microscopy (OM), Scanning Electron Microscopy (SEM) & Energy Dispersive X- Ray spectroscopy (EDX) analyses have been carried out on the 3D printed samples. The microstructural observation indicated very low porosity with homogeneous composition throughout the specimen. A layer by layer structure with columnar grains grown in the direction of heat transfer were clearly seen in the microstructure.
A-124: Microstructural Characterization of Ni-based Multilayer Coating After Laser Cladding on Cast Iron Substrate: Fazati Bourahima1; Michel Rege1; Christophe Lafarge1; Abderazak Khenafi1; 1CHPOLANSKY
Laser cladding of a Ni-based powder on cast iron molds was performed with a 4kW Nd: YAG laser. The cast iron is used as a thermal exchanger in glass mold industry. But the issue of this material is its poor resistance to corrosion and abrasion. The role of the Ni-based alloy is to protect the mold without affecting its thermal properties. The purpose of this research is to produce multilayer coating without pores or cracks and with a very small dilution zone on a complex surface. The impact of the processing parameters, power (1400 - 2200 W) and scanning speed (0.6 - 4.6 mm/s) on the coating microstructure was investigated with SEM analysis, microhardness and residual stress tests. The influence of the dendrites growing direction during solidification on porosity and cracks appearance was noted. An optimization of the processing parameters is proposed by using a statistical method, analysis of variance.
A-125: Microstructure and Mechanical Properties of AISI420 Stainless Steel Produced by Wire Arc Additive Manufacturing: Jonas Lunde1; Mostafa Kazemipour1; Salar Salahi1; Ali Nasiri1; 1Memorial University of Newfoundland
Wire arc additive manufacturing (WAAM) with a high deposition-rate and reduced feedstock material’s waste was used to fabricate thin walls of AISI420 stainless steel (SS). The microstructure of the fabricated wall was investigated in detail utilizing optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD), while mechanical properties were characterized by conducting Vickers microhardness measurement and uniaxial tensile testing. The results demonstrate that the as-printed microstructure of WAAM-420 SS is mainly composed of a martensitic matrix along with chromium-rich carbide particles and delta-ferrite phase. Comparing the obtained yield strength (YS), ultimate tensile strength (UTS), and elongation of the fabricated wall along the deposition direction versus the building direction revealed anisotropic mechanical properties, confirming a better performance along the deposition direction than that of the building direction. The correlations of the as-printed microstructure and the measured mechanical properties of the fabricated wall are discussed thoroughly.
A-127: Microstructure and Mechanical Properties of In 718 Alloy Manufactured by Several Different Process: Seungmun Jung1; Suk h=Hoon Kang1; Chang-Kyu Rhee1; 1KAERI
Research about additive manufacturing is increasing because of their high potential in variety industries like aerospace, automobile, plant etc. Additive manufacturing has a near-net-shape process brought not only reducing time and cost, but also could manufacturing complex shape product. A number of manufacturing processes like Powder Bed Fusion (PBF), Direct Energy Deposition (DED) are available. According to manufacturing process, materials has different solidification process and thermal-cycle which determine the microstructure and properties of materials. In this study, we manufactured Ni super alloy (Inconel 718) by different additive manufacturing process (PBF, DED, Arc-DED). Each materials evaluated the mechanical properties and analyzed the microstructure.
A-128: Microstructure and Mechanical Properties of Ti/TiC Composite Coatings Fabricated by Laser Engineered Net Shaping: Madhavan Radhakrishnan1; Zeynel Guler1; Md Mehadi Hassan1; Thomas Lienert2; Osman Anderoglu1; 1University of New Mexico; 2Optomec Inc
Titanium/titanium carbide mixtures with the TiC contents of 20, 40 and 60vol.% were successfully deposited onto Ti64 substrates by Laser Engineered Net Shaping process. The process produced a well-bonded and continuous interface between the coating and substrate. From cross-sectional microstructural examination, the coatings comprise three different morphologies of TiC phase embedded in Ti matrix: angular particles from feed mixture, dendritic and equiaxed particles from the solidification of melt pool. The compositional differences in different carbide particles have been identified using the XRD and EPMA techniques. The heat affected zone in Ti64 substrate, near the interface, showed needle-shaped features that suggests martensitic transformation of the parent phase. Here, the correlation of mechanical properties of coatings and volume fraction of different resolidified TiC particles with TiC volume fraction will be discussed. A possible means towards the prediction of mechanical properties in a printed material using machine learning methods will be described.
A-129: Nonlinear Coupling Effect Analysis of Material Properties, Processing Parameters and Part Geometry in Metal Additive Manufacturing by Full-scale Layerwise Additive Manufacturing Simulation Tool: Jinquan Cheng1; 1CS3DM
Metal additive manufacturing is using various heat sources to sinter/melt the fine powder track by track and layer-by-layer for fabrication part. The inherent heat and mass transfer are nonlinearly coupled by the material properties, structure geometry and processing parameters. To reveal the nonlinear coupling effect, a full-scale analysis of thermophysical response is very important and necessary. To overcome the simulation limitation, an analytical block technique was developed for the full-scale simulation and realistically emulate the temperature field change. The main processing parameters: speed, energy, layer thickness, hatch distance, deposit pattern etc. and part geometry were considered. From the simulation, it is seen that the temperature field nonlinearly changes subjected to the change of material properties, part geometry and size, and processing parameters. The relationship among the temperature, temperature gradient, cooling rate, key processing parameters and geometry and size were built up for the designer to better understand the nonlinear effects.
A-130: Numerical Prediction of Microstructures by a Coupled Model (CA-FE) for Laser Beam Melting of Single-track 316L Stainless Steel: Anaïs Baumard1; Danièle Ayrault1; Olivier Fandeur1; Anne-Laure Vételé1; Cyril Bordreuil2; Frédéric Deschaux-Beaume2; 1Den-Service d'études Mécaniques et Thermiques (SEMT), CEA; 2LMGC, University Montpellier, CNRS
Laser Beam Melting (LBM) refers to an additive manufacturing process that enables the realization of objects from powder melted by a laser beam. Additive processes offer advantages (manufacturing time and losses reductions, fabrication of complex geometries). Nevertheless, the fusion process occurs during high-speed laser scanning and so generates anisotropic microstructures, influencing the mechanical properties. Therefore, solidification modeling is required for a better understanding of grain formation during LBM. In this work, the numerical modeling used for this purpose, based on a three-dimensional “CAFE” model, is presented. It couples Cellular Automaton (CA) simulating the solidification of 316L stainless steel, and Finite-Element (FE) providing temperature fields. The numerical modeling of the process is based on experimentations and is being validating comparing numerical and simulated thermal fields, shape and size of the molten zone. To conclude, a cellular domain is defined to investigate grain structure predictions that are compared with some EBSD results.
A-131: On the Heat Treatment of AlSi10Mg Alloy Fabricated by Selective Laser Melting Process: Catherine Dolly Clement1; Julie Masson2; Abu Syed Kabir1; 1Carleton University; 2Institut Supérieur de l'Aéronautique et de l'Espace
AlSi10Mg is the most widely additively manufactured and commercialized aluminum alloy. In this study, AlSi10Mg specimens were manufactured by selective laser melting process followed by post-process heat treatment at various temperatures. Microstructures were characterized by optical and electron microscopes and mechanical properties were studied by micro-indentation hardness and tensile tests. Various phases were analyzed by X-ray Diffraction (XRD) and Electron Probe Micro-Analyzer (EPMA) techniques. Observation shows that it’s nearly impossible to completely dissolve the evolved second phase silicon particles which may have significant effects on the mechanical characteristics. Back Scattered Electron imaging results show the evolution of iron-rich particles in the aluminum matrix which may have significant influence on the mechanical properties of the alloy.
A-132: On the Influence of Nitrogen on the Performance of Austenitic Stainless Steel 316L Processed by SLM: Julia Richter1; Thomas Niendorf1; 1University of Kassel, Institute of Materials Engineering - Metallic Materials
Selective Laser Melting (SLM) is a metal-powder based layer-by-layer additive manufacturing technique, where powder is distributed in thin layers and subsequently melted by a laser only guided by a CAD-file. The SLM process is widely used for processing of the titanium alloy Ti6Al4V, the nickel-based alloy Inconel 718 and the austenitic stainless steel 316L. These materials have been studied numerously upon processing under inert argon atmosphere and correlations between processing parameters and microstructural as well as mechanical properties are available. In the current study, 316L was processed under nitrogen atmosphere. The change of process gas results in different parameters needed for robust processing. This is due to different heat dissipation in the built process eventually leading to changes in microstructure and mechanical properties. The study comprises the microstructural analysis of the as-built condition as well as characterization of mechanical properties under quasi-static and cyclic loading.
A-133: On the Microstructure and Corrosion Behavior of Wire Arc Additively Manufactured AISI 420 Stainless Steel: Mostafa Kazemipour1; Jonas Lunde1; Salar Salahi1; Ali Nasiri1; 1Memorial University of Newfoundland
In this study, a robotic wire arc additive manufacturing (WAAM) technology utilizing advanced surface tension transfer mode was adopted to fabricate a thin wall of AISI 420 stainless steel. The microstructure and corrosion properties of the as-printed wall were studied and compared to its wrought counterpart. Optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) analysis were used to determine the microstructure of the wall. The dominant microstructure of the wall comprised 𝛿-ferrite phase and carbides micro-constituents embedded in a martensitic matrix, revealing a gradual decrease in the amount of formed carbides from the bottom of the wall towards its top. The corrosion behavior of the wall was evaluated using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PD) testing. As a general trend, the upper portion of the fabricated wall revealed an improved corrosion resistance and reduced pitting susceptibility than the bottom layers.
A-134: On the Role of Defects in the Dynamic Response of AM SLM 316L: Liam Smith1; David Chapman1; Paul Hooper2; Daniel Eakins1; 1University of Oxford; 2Imperial College London
AM materials have differing texture to CM counterparts, with AM material also suffering from defects including cracking, lack-of-fusion porosity and element segregation. Understanding the effects of these on dynamic material response is key to adopting these materials into real-world applications. Several highly instrumented reverse (anvil-on-rod) Taylor tests were conducted to evaluate the constitutive response of AM and CM 316L steel. These tests produce a wide range of stresses, strains and strain-rates, allowing strong validation of constitutive models. Potential anisotropic behaviour was explored by comparing the behaviour of AM cylindrical samples manufactured parallel and perpendicular to the build direction. Experimental data from multiple tests were incorporated into an LS-DYNA optimisation routine, which sought to match experimentally measured material responses by varying material parameters in two established constitutive models (JC/ZA). Disparities in optimised material parameters offer comparisons of dynamic response between materials and demonstrate the importance of understanding AM microstructural characteristics.
A-135: On the Size Effects in Additively Manufactured Titanium and the Implications in AM Components: Daniel Barba Cancho1; Carles Alabort2; Roger Reed1; Enrique Alabort3; 1University of Oxford; 2Universidad Politecnica de Valencia; 3OxMet Technologies
The properties of additively- and conventionally-manufactured Ti-6Al-4V are different. The complex geometries in AM lead to significant property variations within a component - which depend upon the temperature gradients of the process. For the first time, in this work, the influence of the specimen size and orientation on the strength and ductility of additive manufactured Ti-6Al-4V is analysed and rationalised in a complete framework. First, the mechanical properties are addressed - as a function of surface-type, orientation, and size. Our results show systematic strengthening and severe drop in ductility as the material section is reduced. These are linked to microstructural and chemical variations. Strengthening is due to refinement of alpha-laths and prior-beta grains and oxygen enrichment. Ductility loss is due to poor surface quality and increased texture. Finally, these findings are used to develop conceptual design maps of strength-ductility as a function of the component type, thickness, and orientation.
A-136: Phase Transformation Kinetic Pathway in Heat Treatment of Ti-6Al-4V Manufactured by Selective Laser Melting: Dang Khoa Do1; Peifeng Li1; 1University of Glasgow
The Selective Laser Melted Ti-6Al-4V consists of an acicular martensitic microstructure (’) in as-built conditions owning to fast cooling rate. In the post process, high temperature decomposes the ’ into + microstructure as final products. However, the kinetic pathways of the phase transformation is not well established and the intermediate path via the spinodal decomposition, ’ → (solute-rich) + (solute-lean) → + is often neglected in the literature. Therefore, we proposed the possible pathway by employing the thermodynamic graphical approach coupling with Phase Field modelling and experiment. The result has successfully explained the spinodal decomposition mechanism of the ’ into the Vanadium-rich and the Vanadium-lean and the association with annealing twins in the heat treatment of Selective Laser Melted Ti-6Al-4V
A-137: Phase-field Method for Grain Evolution During Additive Manufacturing: Alexander Chadwick1; Peter Voorhees1; 1Northwestern University
Models of the solidification process during additive manufacturing are central to predicting the microstructure of the resulting build. Quantitative phase-field models have been successful in studying traditional solidification processing of metals; however, these models typically assume the presence of local equilibrium at the solid/liquid interface which cannot be assumed a priori in rapid solidification. Here, we present a study of phase-field models at velocities where complete solute trapping and absolute stability of planar interfaces occur. We examine the behavior of these models and identify limitations that would either lead to prohibitive computational cost or inaccuracies in the predicted solidification behavior in both the isothermal and nonisothermal regimes. We will present modifications and numerical techniques that ameliorate these limitations. Lastly, we will demonstrate the capabilities of the new model by predicting the preferred crystallographic orientations that arise during powder bed fusion of a polycrystalline structural alloy.
A-138: Powder Flowability Measurements: Statistical Correlations Between Powder Characteristics and Flowability Behavior: Parnian Kiani1; Umberto Scipioni Bertoli1; Alexander Dupuy1; Kaka Ma2; Julie Schoenung1; 1University Of California, Irvine; 2Colorado State University
The quality of parts fabricated with additive manufacturing is often influenced by the flowability of the feedstock particles, which is often the result of many factors, including chemistry (e.g., material density, the presence of surface oxides), morphology (e.g., particle shape), and particle size distribution. This work investigates the relationship between powder characteristics and flow behavior of different powders by using three different flowability testing method (rheometry, avalanche, and funnel). Six powders of two compositions (stainless-steel and AlSi10Mg), made using two different methods (gas- and water-atomization), were investigated to rationalize the effect of powder chemistry and morphology on flow behavior. Often, different flowability metrics were found to statistically correlate with one another, providing similar information. Additionally, individual powder flowability metrics were often strongly correlated with one morphological feature, such as particle aspect ratio. Finally, some measurements exhibited strong sensitivity to powder composition and density.
A-139: Precipitation Behavior and Its Strengthening Effect of Maraging Steel in Laser Cladding Remanufacturing: Ke Ren1; Yiming Rong1; Shaopeng Wei2; Wei Xing1; Gang Wang2; 1Harbin Institute of Technology; Southern University of Science and Technology; 2Tsinghua University
Laser hot-wire cladding is one of the major remanufacturing processes used to repair damaged compressor impellors. The strength of cladding layer and heat-affected zone (HAZ) is essential to the functionality and reliability of repaired parts. This paper made a qualitative explanation of strength variation by analyzing the microstructure of the substrate. Thermal simulation experiment was conducted to investigate the effect of aging temperature on the strength of the substrate. Results showed that the strength trend in the cladding layer and HAZ varied with respect to the aging temperature as a result of precipitation behavior. Heat treatment temperature was divided into three interval depending on its effect. Further, the tip temperature of substrate solid solution was found out to be 500℃. Precipitates coarsening and dissolution in aging state substrate led to heat affected zone softening.
A-141: Process Plateaus, Not Peaks, in Laser-powder Bed Fusion: Bradley Jared1; Josh Koepke1; Jarrett Tigges1; Michael Heiden1; David Saiz1; 1Sandia National Laboratories
Metal laser-powder bed fusion (L-PBF) involves numerous process inputs which must be established to insure the reliable fabrication of part material and geometry. Work has been performed on 316L stainless steel to quantify its parameter space relative to laser power and laser scan velocity. Multiple performance metrics were evaluated including surface roughness, geometrical form error, material density, microstructure and mechanical properties. It has been discovered that the process space for L-PBF 316L involves a viable process window that is much more of a plateau area than an optimized peak. It has also been determined that establishing process settings based solely on material density, a common practice in the industry, is likely not truly optimal. These results, and their potential impact on part performance will be discussed. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.
A-142: Processing Parameters Optimization on Additively Manufacturing Pure Magnesium for Quality Improvement: Experiments and Simulations: Jinquan Cheng1; Bandar AlMangour2; 1CS3DM; 2Saudi Arabia Basic Industries Corporation
Mg-based materials are known for their low density as well as high biocompatibility, which makes them suitable for lightweight structural and biomedical applications. Additive manufacturing technique is one of free-form fabrication technique and enable to any complex structure in a track-by-track and then layer-by-layer manner. This study explores the use of selective laser melting (SLM) to additively manufacture the magnesium component and investigates the densification behavior, microstructural evolution, and mechanical properties of pure Mg processed by SLM under various processing parameters. The challenges associated with the SLM-processability of Mg were addressed. Based on the experimental results, Layerwise Additive Manufacturing Predictions and Simulations (L.A.M.P.S.) Tool was applied to numerically reveal the inherent relationship among part quality, material properties and processing parameters. Through the numerical analysis, the simulation results help designer to tailor the processing parameters and reduce the experimental deposition.
A-143: Residual Stress Mitigation in Metal Additive Manufacturing Using Compositional Engineering: Aleksandra Vyatskikh1; Baolong Zheng1; Umberto Scipioni Bertoli1; Enrique Lavernia2; Julie Schoenung1; 1Department of Materials Science and Engineering, University of California, Irvine; 2Department of Materials Science and Engineering, University of California
Broad application of additive manufacturing (AM) has been hindered by a lack of fundamental understanding of the formation and evolution of process-related defects, notably porosity and residual stress. Common residual stress mitigation approaches, including in situ heating, adaptive scanning strategies, and post process annealing, are unable to fully eliminate residual stress. We demonstrate a complimentary residual stress mitigation strategy based on compositional engineering. We use gas atomization to synthesize custom Fe-Cu alloyed powders with varying Cu content. We then use Laser Engineered Net Shaping (LENS®) to fabricate AM samples. We investigate residual stress by employing XRD and hole drilling methods. Using this approach, we study the influence of composition on residual stress in the AM parts. We employ optical microscopy, SEM/EDS, EBSD, XRD and TEM to investigate the resulting microstructure and composition. Our findings suggest that compositional engineering is a feasible strategy to efficiently mitigate the residual stresses in AM.
A-144: Residual Stress Mitigation in Selective Laser Melting Through Laser Scan Strategy Optimization Using Machine Learning: Kahraman Demir1; Charles Yang1; Adi Ben-Artzy1; Jack Peterson1; Grace Gu1; Peter Hosemann1; 1University of California, Berkeley
Selective laser melting has enabled for the fabrication of geometries that would otherwise be impossible or impractical to fabricate with conventional technologies. However, high thermal gradients, resulting from rapid localized heating and cooling, cause the development of intense residual stress fields within the material of the fabricated part which leads to poor fracture properties, poor dimensional tolerances, inconsistent material properties and fabrication failures. Among many process parameters, laser scan strategy significantly influences the development of residual stresses in the fabricated part. In this work, a macroscale thermomechanical finite difference model is used to predict the residual stresses in single layers subjected to different laser scan patterns. These pattern parameters are then coupled with values quantifying the intensity of the residual stress fields and analyzed using machine learning to investigate potential correlations and to gain new insights on residual stress mitigation techniques when generating scan trajectories.
A-145: Simultaneously Improved Thermophysical and Mechanical Properties of Additively Manufactured Cu-Ni-Sn-P Alloy Through Aging Heat Treatment: Young-Kyun Kim1; Dong-Hoon Yang1; Sun-Hong Park2; Kee-Ahn Lee1; 1Inha University; 2Research Institute of Industrial Science and Technology
This study used selective laser melting (SLM) to manufacture a multi-functional Cu-Ni-Sn-P alloy and investigated the effect of homogenization and aging heat treatments on the microstructure, mechanical- and thermophysical-properties. Initial microstructural observation confirmed that the as-built alloy was composed of Cu, Cu6Sn5,, Cu3P and undissolved Ni phases. After the homogenization, the Cu-Ni-Sn alloy shows Cu-Ni solid-solution and (Cu,Ni)3P phases. On the other hands, elemental composition of Ni in (Cu,Ni)3P phase increased with increasing aging time. Vickers hardness measurements showed 69.6HV and 225.1HV in the homogenized alloy and 4H-aged alloy, respectively. Furthermore, compressive yield strengths of homogenized- and aged-sample showed same tendency with hardness, showing remarkable improvement in mechanical properties. Meanwhile, as aging time increased, thermal conductivity also increased about 26%. It is due to the decreasing frequency of lattice collision of electrons in solid-solution. Based on these findings, the optimum combination of mechanical- and thermophysical properties was also discussed.
A-148: Tailoring Hierarchical Material Performance Through Process Manipulation: Bradley Jared1; David Saiz1; Michael Heiden1; Matthew Roach1; Anthony Garland1; Brad Boyce1; Ben White1; David Moore1; 1Sandia National Laboratories
Hierarchical materials introduce a compelling design space to achieve material and structural performance regimes that are inaccessible in bulk, homogenous materials. Numerous researchers have explored an array of geometrical constructs for tuning hierarchical material properties. The presented work, however, will explore how process inputs from laser-powder bed fusion impact the mechanical performance of 316L stainless steel octet and gyroid lattice structures. The process space within which robust lattice geometries can be fabricated will be described. Relationships between process inputs and resultant strut geometry, cell geometry and structure performance will also be presented based on fringe-project microscopy, computed tomography, metallography and quasi-static compression loading. Thus, it will be demonstrated that process inputs provide an additional degree of freedom in the design and fabrication of hierarchical materials. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.
Cancelled
A-149: The Effect of Support Structures on Microstructure in LPBF and EBM: Sandra Megahed1; Vadim Aniko1; Maximilian Voshage1; Johannes Henrich Schleifenbaum2; 1Chair of Digital Additive Production, RWTH Aachen University; 2Chair of Digital Additive Production, RWTH Aachen University; Fraunhofer-Institute for Laser Technology ILT
The design freedom of Additive Manufacturing is an important advantage. Overhanging structures in need of support structures limit this freedom in Laser Powder Bed Fusion (LPBF). Support structure design affects heat transfer and final component microstructure. As opposed to LPBF, during Electron Beam Melting (EBM) every powder layer is preheated and consequently sintered prior to selectively melting the powder. Sintered powder layers withstand loads reducing the need for support structures. The necessity of support structures in EBM is determined for Ti64 parts and compared to LPBF regarding overhang angle and length. Heat dispersion in sintered (EBM) powder is more uniform than in loose powder (LPBF) resulting in differing microstructures, which are compared in terms of grain size and orientation. The influence of different support structure designs and varying solidification conditions on component microstructure is investigated. The extent of distortion in EBM as compared to LPBF is experimentally and numerically quantified.
A-151: The Effects of LENS Process Parameters on the Behavior of 17-4 PH Stainless steel: Ipfi Mathoho1; Esther Akinlabi2; Nana Arthur1; Monnamme Tlotleng1; 1CSIR Pretoria; 2University of Johannesburg
17-4 PH stainless steel has proven to be one of the workhorse material in industries such as aerospace, chemical and energy. The attraction of this alloy to the aforementioned industries is derived from the fact that 17-4 PH stainless steel possesses a combination of excellent mechanical properties and corrosion resistance. Manufacturing of 17-4 PH stainless steel through 3D printing will further inspire confidence to the aforementioned industries. The current study investigated the effects LENS process parameters on porosity, microstructure, and microhardnesss. The scanning speed, and powder feed rate were varied at 7.62 mm/s-12.7 mm/s and 4.70 g/min-5.98 g/min rpm respectively, while laser power was kept constant at 300 W. The optimum scanning for both 4.70 g/min and 5.98 g/min was 10. 16 mm/s and 12.7 mm/s respectively. The current study deduced that varying both scanning speed and powder feed rate had an impact on both the microstructure and microhardnessKey words: 17-4 PH stainless steel, LENS, Microhardness, Microstructure, porosity
Cancelled
A-152: The Process Parameters Extended Criterion for Laser Engineered Net Shaping of Inconel 738: Yang Zhou1; Zhaoyang Liu1; Chuan Guo1; Guowei Ye1; Xin Li1; Qiang Zhu1; 1Southern University of Science and Technology
Laser engineered net shaping processing has been an efficient technique for the rapidly manufacturing high-temperature superalloy parts in recent years. While, for the high-crack-susceptibility superalloy such as Inconel 738 alloy, the current flawless processing window is very narrow and resultantly limits the application of laser engineered net shaping processing in the area of turbine engines due to discreteness and complexed mutual correlation of the process parameters. In this work, experiments were conducted to study the effect of processing parameters such as laser power and scanning speed on the formability, especially the crack formation and distribution, of laser manufactured Inconel 738 alloy. The results indicate that the element Ti segregation and low-meting-point γ/γ՛ eutectic generation at the high angle grain boundary lead to continuous liquid film form during heating process, and then generates cracks under the induction of inclusions such as carbides during the cooling of periodic depositing process. Reducing the element Ti segregation by optimizing processing parameters and suppression the remolten of γγ՛ eutectic during the periodic depositing process can efficiently expand the flawless window for the directly manufacturing Inconel 738 alloy by laser engineered net shaping process.
A-153: The Significance of Length Scales and Segregation in Strengthening Selective Laser Melted Stainless Steel Microstructures: Tatu Pinomaa1; Matti Lindroos1; Martin Walbrühl2; Nikolas Provatas3; Anssi Laukkanen1; 1VTT Technical Research Centre of Finland; 2Royal Institute of Technology (KTH); 3McGill University
The mechanical properties of additively manufactured 316L steel depends strongly on the cellular rapid solidification microstructure. In this work, we connect processing conditions to the resulting microstructure, and relate this further to the micromechanical response. Directional phase field simulations are used to generate process-microstructure maps. The phase field model is mapped to have controlled solute trapping behavior and to follow the kinetics of continuous growth model, through matched interface asymptotics. The cell spacings are compared to experiments from the literature. The generated cellular structures are analyzed with a Cosserat micromechanical crystal plasticity model, which takes into account local solid solution strengthening variation, microstructural length scale effects, and hardening effects. Micromechanical in polycrystalline structures are analyzed. We show that the cell spacing and solute segregation affect the overall hardening behavior, and also influence plastic localization and geometrically necessary dislocation (GND) type hardening.
A-154: Thermodynamic Calculation and Characterization of Carbide Precipitation in Laser-deposited Material for High Speed Steel Alloy: Ali Jammal1; Gang Wang1; Songge Yang2; Yu Zhong2; Yiming Rong3; 1Tsinghua University; 2WPI; 3Southern University of Science and Technology
The laser cladding of the T15 high speed steel was accomplished and its typical microstructure was determined. The microstructure characterization of the clad layer showed three phases of microstructure, planar, cellular and equiaxed zones. Electron probe micro-analyzer (EPMA) showed high content in alloying elements at the cellular and equiaxed zones that contained V, C, Cr and W. Further, the analysis at the inter-granular zone presented the highest concentration in elements such as Mo, Cr and W. This showed the presence of carbides which were identified as MCI and M6C at the cellular zone, and M7C3 and M27C6 at the equiaxed and inter-granular zones. The alloying elements characterization starting from the substrate and passing through the clad layer identified the austenite matrix and revealed the fluctuation in the alloying elements content. Equilibrium phase diagram thermodynamic calculation proved the presence of MCI, M6C and M27C6 which precipitated respectively as the solidification proceeded.
A-155: Thermoelectric Magnetohydrodynamic Effects in Laser Additive Manufacturing: Coupled Macro-microscale Numerical Modelling: Andrew Kao1; Teddy Gan1; Catherine Tonry1; Ivars Krastins1; Koulis Pericleous1; 1University of Greenwich
Strong fluid flow appears in laser additive manufacturing weld pools, with large thermal gradients introducing buoyancy and Marangoni forces. The large thermal gradients also generate significant thermoelectric currents, which in the presence of a magnetic field drive flow, the so called thermoelectric magnetohydrodynamics (TEMHD) phenomenon.TESA, the purpose-built Thermoelectric Solidification Algorithm, uses a lattice Boltzmann enthalpy based method to capture the macroscopic melt pool dynamics. There is competition between Marangoni and the magnetically induced flows, where the orientation and strength of the magnetic field leads to a deepening, widening or even a deflection in the melt pool. The macroscopic model is coupled to a microscopic crystal growth model that predicts the resulting microstructure, accounting for flow, multiple additive layers, time/spatially varying magnetic fields and scanning strategy. The results show that judicious use of the magnetic field can disrupt key defects, such as that of epitaxial growth.