Browsing by Author "Wicker, R.B."

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A comparison of the mechanical behavior of AlSi7Mg alloy produced through additive manufacturing and subjected to different heat treatment and aging conditions
(University of Texas at Austin, 2023) Caballero, K.; Medrano, V.A.; Arrietam E.; Merino, J.; Ruvalcaba, B.; Ramirez, B.; Diemann, J.; Murr, L.E.; Wicker, R.B.; Godfrey, D.; Benedict, M.; Medina, F.
The versatility and adaptability of Aluminum F357 (AlSi7Mg) make it a popular material in the aerospace and defense industries. In this study, two different laser powder bed fusion systems, EOS M290, and SLM 280HL were used to create specimens of Aluminum F357. These specimens were subjected to five different heat treatments: As-built, stress relief (SR), hot isostatic pressing (HIP), T6, and HIP+T6) as per ASTM F3318-18 standard. The printed specimens were then reduced to tensile bars through machining and tested for mechanical properties as per ASTM E28 using an MTS Landmark tensile testing system. In addition to the mechanical behavior analysis, the study used a JEOL JSM-IT500 SEM to observe and document the fracture produced by the tensile test and a Qness 30 CHD Master+ microhardness testing system to obtain hardness (HV) values of the alloy. The results showed that specimens fabricated in the Z direction had a tendency for higher yield strengths of approximately 225 MPa and although these results were similar between LPBF systems some variances can still be seen. However, these differences between the LPBF systems were observed to be partially mitigated by heat treatments. In conclusion, this study highlights the significance of heat treatment on the mechanical properties of Aluminum F357. The results provide valuable information for the aerospace and defense industries to optimize their processes and produce high-quality components. The compatibility of LPBF system fabrication and the mitigation of differences observed between LPBF machines by heat treatments, further demonstrate the potential of this method for producing high-quality Aluminum F357 components.
Automatic Layerwise Acquisition of Thermal and Geometric Data of the Electron Beam Melting Process using Infrared Thermography
(University of Texas at Austin, 2014) Ridwan, S.; Mireles, J.; Gaytan, S.M.; Espalin, D.; Wicker, R.B.
Layerwise monitoring has become an area of interest in the field of additive manufacturing because of potential to further enable part qualification during every stage of fabrication. Spatial monitoring and qualification during part fabrication has never before been possible with traditional manufacturing processes such as milling or casting. An IR camera has been externally annexed atop an EBM system to obtain layerwise thermographs throughout the fabrication process. This paper demonstrates a process to compare each layer of fabrication using automatically acquired thermal images to the corresponding CAD file for each fabricated object. Two different methods of image analysis for part detection were compared (analysis on the basis of color and analysis by edge detection). Detection allowed the quantification of processing information (average temperature and surface anomalies) and geometric information (surface area and perimeter). A percent error of the compared surface area was found to range from 5%- 17%, and automatically acquired temperature measurements were within 7.8K of the recorded thermograph. The methods presented in this research showcase the beginning steps of integrated metrology in advanced manufacturing systems and automatic monitoring of per-part thermal behavior and part quality.
Comparison of Microstructures and Mechanical Properties for Solid Cobalt-Base Alloy Components and Biomedical Implant Prototypes Fabricated by Electron Beam Melting
(University of Texas at Austin, 2010-09-23) Gaytan, S.M.; Murr, L.E.; Martinez, E.; Martinez, J.L.; Machado, B.I.; Ramirez, D.A.; Medina, F.; Collins, S.; Wicker, R.B.
The microstructures and mechanical behavior of simple, as-fabricated, solid geometries (with a density of 8.4 g/cm3), as-fabricated and fabricated and annealed femoral (knee) prototypes all produced by additive manufacturing (AM) using electron beam melting (EBM) of Co-26Cr-6Mo-0.2C powder are examined and compared in this study. Microstructures and microstructural issues are examined by optical metallography, SEM, TEM, EDS, and XRD while mechanical properties included selective specimen tensile testing and Vickers microindentation (HV) and Rockwell C-scale (HRC) hardness measurements. Orthogonal (X-Y) melt scanning of the electron beam during AM produced unique, orthogonal and related Cr23C6 carbide (precipitate) cellular arrays with dimensions of ~2μm in the build plane perpendicular to the build direction, while connected carbide columns were formed in the vertical plane, parallel to the build direction.
Cooperative Fabrication Methodology for Embedding Wireon Corved Surfaces
(University of Texas at Austin, 2014) Kim, C.Y.; Cuaron, A.; Perez, M.A.; Espalin, D.; MacDonald, E.; Wicker, R.B.
In conventional additive manufacturing (AM), an object is fabricated by depositing material in a layer by layer fashion. Typically, this process is retained so that deposition can occur on flat surfaces and motion can be constrained to requiring only three degrees of freedom (DOF) in a Cartesian coordinate system. When incorporating wire in three-dimensional (3D) objects, there is sometimes a need for placement along curved surfaces on which positions are defined not only by 3D Cartesian coordinates but also angular ones. Therefore, a minimum of two additional DOFs are required allowing movement to be generated at the build platform as well as of the extrusion head. This paper addresses a method for trajectory planning of both systems, that is, the extrusion head and the movable build platform, allowing for cooperative and harmonic motion between the two.
EBM Fabrication and Characterization of High Purity Niobium for Superconductor Applications
(University of Texas at Austin, 2014) Terrazas, C.A.; Gaytan, S.M.; Mireles, J.; Frigola, P.; Espalin, D.; Wicker, R.B.
Superconducting radio frequency (SRF) cavities are used to accelerate charged particles to near the speed of light for elemental studies. Currently, SRF cavities are typically fabricated using different forming processes including deep-drawing and spinning to mechanically shape niobium into the desired geometry. This research presents the development of processing parameters for high purity niobium (powder size range of 25-125μm) using electron beam melting additive manufacturing technology. Fabrication parameters were improved to obtain dense parts in a time-efficient manner. A specific procedure was used to maintain powder purity, and powder chemistry was monitored at different stages of fabrication. In addition, a series of experiments were performed to obtain 99.9% dense parts and a maximum building height of ~85mm.
Effect of Build Parameters and Build Geometries on Residual Microstructures and Mechanical Properties of Ti-6Al-4V Components Built by Electron Beam Melting (EBM)
(University of Texas at Austin, 2009-09-15) Murr, L.E.; Gaytan, S.M.; Medina, F.; Martinez, E.; Hernandez, D.H.; Martinez, L.; Lopez, M.I.; Wicker, R.B.; Collins, S.
In this study, involving additive manufacturing (AM) using electron beam melting (EBM), we have examined build defects which result from beam tripping, porosities (including unmelted or unsintered zones) due to excursions from optimal build parameters (especially variations in melt scan beam current and scan speed), and gas bubbles trapped in atomized Ti-6Al-4V starting powder as well as recycled powder, and retained in the build. At optimized build conditions we have also examined microstructure-mechanical property (hardness, tensile strength, and elongation) variations for multiple rake building and multiple melt scans using optical metallography and scanning and transmission electron microscopy (SEM and TEM). These build variances cause cooling rate variances which promote α-phase growth and variations in dislocation density, as well as α-to-α' (martensite) phase changes, all of which produce some degree of mechanical property variations. These features (especially α-to-α' phase changes) are notable on comparing solid builds in comparison with a variety of mesh arrays where strut dimension and build-element complexities alter the cooling rates in a significant way. We illustrate these microstructure variations with corresponding variations in microindentation hardness measurements made directly on fine mesh (strut) structures. Finally, we have examined Ti-6Al-4V powder chemistries and solid build chemistries which for single-pass melt scans at optimized build conditions are shown to be relatively constant up to 40 cycles of powder reuse with the exception of Al content which was reduced by 10 to 15% in solid builds at optimized conditions. However, Al loss in solid builds approached 25% for multiple (2 and 3) melt scans, while no changes in Ar gas-bubble density were observed with changes in α-phase (grain) width which increased from 3 µm for a single melt scan to 4.5 and 6 µm for 2 and 3 melt scans, respectively. Corresponding Rockwell C-scale (HRC) hardness varied from 37, 36, and 35, respectively; with ultimate tensile strengths exceeding 1.2 GPa at elongations of 12% or higher for this melt scan sequence.
Expanding the Applicability of FDM-type Technologies Through Materials Development
(University of Texas at Austin, 2014) Roberson, D.A.; Shemelya, C.M.; MacDonald, E.; Wicker, R.B.
Currently, the most common form of additive manufacturing is material extrusion 3D printing (ME3DP) based on fused deposition modeling (FDM®) technology which relies upon a thermoplastic monofilament as a base material for the fabrication of three dimensional objects. The dependence on thermoplastics as a feedstock by ME3DP platforms limits the applicability of this additive manufacturing method. A clear-cut path towards greater applicability is the introduction of novel materials with diverse physical properties which maintain compatibility with 3D printing platforms based on FDM® technology. The work in this paper presents efforts in the development of polymer matrix composites (PMC)s and polymer blends based on acrylonitrile butadiene styrene (ABS) and polycarbonate (PC), two thermoplastic materials commonly used by FDM®-type platforms. Mechanical testing and fractography via scanning electron microscopy (SEM) were the two main metrics used to characterize these new material systems. Overcoming barriers to the manufacturing of these novel 3D-printable materials systems is also presented.
EXPLORING IN718 ALLOY PRODUCTION WITH BI-DIRECTIONAL RASTER AND STOCHASTIC SPOT MELTING TECHNIQUES USING AN OPEN-SOURCE ELECTRON MELTING SYSTEM
(University of Texas at Austin, 2023) Nabil, S.T.; Banuelos, C.; Ramirez, B.; Cruz, A.; Watanabe, K.I.; Arrieta, E.; Wicker, R.B.; Medina, F.
This study compares the fabrication of IN718 alloy using bi-directional raster and stochastic spot melting techniques with the open-source FreemeltOne Electron Beam Melting (EBM) system. The research aimed to produce dense parts using both scanning strategies, employing custom Python code for raster melt beam path generation and PixelMelt software for stochastic spot melting path generation. After optimizing process parameters, 10mm height builds for each scanning strategy were fabricated, and their microstructure, hardness, and density were analyzed using optical microscopy and SEM, Vickers microhardness scale, and a pycnometer. The findings reveal valuable insights into the effects of scanning strategies on the microstructure, hardness, and density of IN718 alloy components, advancing additive manufacturing knowledge.
Fatigue Endurance Investigation of Post-processed Surfaces of LPBF Ti-6Al-4V under Flexural Stress
(University of Texas at Austin, 2023) Banuelos, C.; Ramirez, B.; De la Cruz, A.; Nabil, S.T.; Arrieta, E.G.; Wicker, R.B.; Medina, F.
Numerous research works can be found focusing on fatigue properties of AM components, however most of this literature is focused on uniaxial testing. Because the very few actual components under uniaxial loading conditions found in any application, it is also important to investigate fatigue performance under loads that produce combined stresses, such as bending. This project investigates the fatigue endurance of LPBF Ti-6Al-4V specimens subjected to four different surface finishing prost-processes (milled, ground, polished and abrasive media). The test consisted of a force-controlled cyclic load applied on the specimen in a 4-point bending setup until fracture. The study incorporated mechanical and optical techniques to measure and quantify the characteristic surface roughness of the post-processes. Additionally, failure mechanisms are discussed on fractographs. The data analyses suggested that internal defects commonly present in additively manufactured parts had a more significant impact on the fatigue life than surface roughness of post-processed parts.
Integrating UC and FDM to Create a Support Materials Deposition System
(University of Texas at Austin, 2009-09-15) Swank, M.L.; Strucker, B.E.; Medina, F.R.; Wicker, R.B.
Currently there is no automated deposition system available for support materials in Ultrasonic Consolidation. Support materials are important to the UC technology because of the benefits that can be geometrically achieved. Without an integrated support materials system many geometries and features will be impossible to create. This paper describes the approach taken to integrate UC and FDM in order to automatically deposit materials as a support in a UC machine. This includes the process setup, design, and planning. Finally a build process integrating the two machines is shown to demonstrate that automated support material deposition in UC is possible.
Microstructural and microhardness variations of laser powder bed fusion (L-PBF) additively manufactured Inconel 718 due to machine variability and wall thickness for aerospace applications
(University of Texas at Austin, 2023) Doris, A.; Trujillo, I.; Godinez, D.; Arrieta, E.; Wicker, R.B.; Gradi, P.; Katsarelis, C.C.; Medina, F.
This paper reports on a study investigating the microstructure and microhardness of thin walls fabricated by Laser Powder Bed Fusion (L-PBF) from sixteen geometric feature build plates. The study evaluated any variance in those properties with the variation in thickness by characterizing the XY and YZ planes of seven thin walls of different thicknesses and the base parts. Electron Backscatter Diffraction (EBSD) analysis with inverse pole figure (IPF) mapping was done for four samples from four different machine manufacturers. From the EBSD grain boundary map, the microstructure is composed of equiaxed grains with a lower threshold angle with smaller grains in the border area. Compositional analysis for both the powders and the resulting fully heat-treated LPBF manufactured material was analyzed for alloy element stability and contaminants using 10 mg samples. The paper concludes by showing the relationship between composition and microstructural properties.
Microstructure Architecture Development in Metals and Alloys By Additive Manufacturing Using Electron Beam Melting
(University of Texas at Austin, 2010-09-23) Murr, L.E.; Gaytan, S.M.; Ramirez, D.A.; Martinez, E.; Martinez, J.L.; Hernandez, D.H.; Machado, B.I.; Medina, F.; Wicker, R.B.
The concept of materials with controlled microstructural architecture (MCMA) to develop and fabricate structural materials with novel and possibly superior properties and performance characteristics is a new paradigm or paradigm extension for materials science and engineering. In the conventional materials science and engineering paradigm, structure (microstructure), properties, processing, and performance features are linked in the development of desirable materials properties and performance through processing methodologies which manipulate microstructures. For many metal or alloy systems, thermomechanical treatment combining controlled amounts of plastic deformation with heat treatment or aging cycles can achieve improved mechanical properties beyond those attainable by conventional processing alone (such as rolling or forging for example) through controlled microstructure development. In this paper we illustrate a new concept involving the fabrication of microstructural architectures by the process development and selective manipulation of these microstructures ideally defining material design space. This allows for the additional or independent manipulation of material properties by additive manufacturing (AM) using electron beam melting (EBM). Specifically we demonstrate the novel development of a carbide (M23C6) architecture in the AM of a Co-base alloy and an oxide (Cu2O) precipitate-dislocation architecture in the AM of an oxygen-containing Cu. While more conventional processing can produce various precipitate microstructures in these materials, EBM produces spatial arrays of precipitate columns or columnar-like features often oriented in the build direction. These microstructural architectures are observed by optical microscopy and scanning and transmission electron microscopy. Prospects for EBM architecture development in precipitation-hardenable Al alloys is also discussed. In the EBM build process using precursor powders, the electron beam parameters (including beam focus, scan speed and sequencing) produce localized, requisite thermodynamic regimes which create or organize the precipitate-related spatial arrays. This feature demonstrates the utility of AM not only in the fabrication of complex components, but also prospects for selective property design using CAD for MCMA development: a new or extended processing-microstructure-property-performance paradigm for materials science and engineering in advanced manufacturing involving solid free-form fabrication (SFF).
RESIDUAL STRESS AND DEFORMATION ANALYSIS OF INCONEL 718 ACROSS VARYING OVERHANGS IN LASER POWDER BLOWN DIRECTED ENERGY DEPOSITION
(University of Texas at Austin, 2023) Hernandez, A.J.; Garcia, D.; Watanabe, K.I.; Gradl, P.R.; Wheeler, K.; Hafiychuk, Halyna; Wicker, R.B.; Medina, F.
Any metal that is subjected to rapid heat and cooling will undergo the development of residual stresses. As they experience intense temperature fluctuations, this will consequently alter the way the material will behave. This issue proves to be of great concern within additive manufacturing. That said, the presence of temperature fluctuations is more prominent in Directed energy deposition (DED), whereas other methods of manufacturing are more prominent in the pre- or post- printing process. This in turn means the deformation, as well as the redistribution of the residual stresses within pieces, are subject to variance by several process parameters set during a print. By using the Inconel 718 alloy feedstock in RPMI’s Laser Powder Directed Energy Deposition (LP-DED) printer, a series of coupons with four different overhang angles and laser power outputs will determine how these changes thermo-mechanically affect the prints through the use of FEA simulations and scans.