@article{vukkum_sanborn_shepherd_saptarshi_basu_horn_gupta_2024, title={Influence of Spatter on Porosity, Microstructure, and Corrosion of Additively Manufactured Stainless Steel Printed Using Different Island Size}, volume={14}, ISSN={["2073-4352"]}, url={https://www.mdpi.com/2073-4352/14/4/328}, DOI={10.3390/cryst14040328}, abstractNote={Specimens of 316 L stainless steel were printed using laser powder bed fusion (LPBF), a popular metal additive manufacturing (AM) technique, with varying island sizes. Not many researchers have considered the impact of spatter while optimizing LPBF printing parameters. In this research, the influence of spatter was considered while also investigating the effect of varied island size on the microstructure, surface roughness, microhardness, and corrosion resistance of LPBF-316 L. No correlation was observed between surface roughness or microhardness and minor variations in island size. However, a correlation was drawn between varied island sizes and porosity in LPBF-316 L. The specimens associated with larger island sizes showed significantly enhanced corrosion resistance due to fewer manufacturing defects and reduced porosity, attributed to the minimal influence of the spatter. Based on analysis, the LPBF parameters were revised, which lead to superior corrosion resistance of LPBF-316 L, attributed to high density and reduced porosity.}, number={4}, journal={CRYSTALS}, author={Vukkum, Venkata Bhuvaneswari and Sanborn, Taylor and Shepherd, John and Saptarshi, Sourabh and Basu, Rakesh and Horn, Timothy and Gupta, Rajeev Kumar}, year={2024}, month={Apr} }
 @article{dejong_horn_kaoumi_2024, title={Review of Solid-State Consolidation Processing Techniques of ODS Steels (Hot Extrusion, Hot Isostatic Pressing, Spark Plasma Sintering, and Stir Friction Consolidation): Resulting Microstructures and Mechanical Properties}, volume={10}, ISSN={["1543-1851"]}, url={https://doi.org/10.1007/s11837-024-06853-3}, DOI={10.1007/s11837-024-06853-3}, journal={JOM}, author={Dejong, Matthew and Horn, Timothy and Kaoumi, Djamel}, year={2024}, month={Oct} }
 @article{ives_bui_habermann_collins_marsden_neilson_horn_rock_2023, title={1.5 MW CW RF Loads for Gyrotrons}, volume={277}, ISBN={["*****************"]}, ISSN={["2100-014X"]}, DOI={10.1051/epjconf/202327704008}, abstractNote={A new series of MW-class, RF loads were developed that can dissipate power levels exceeding 1.5 MW at frequencies from 28 GHz to 180 GHz. The new loads are designed to reflect less than 0.25% of the input power and operate continuously (CW). Stainless-steel and anodized aluminum versions were developed. The stainless steel version is designed to meet requirements for nuclear facilities, such as ITER, while the aluminum version is capable of power levels exceeding 2 MW CW. The aluminum version is also lighter and less expensive. This paper describes the design and capabilities of the loads.}, journal={21ST JOINT WORKSHOP ON ELECTRON CYCLOTRON EMISSION AND ELECTRON CYCLOTRON RESONANCE HEATING, EC21}, author={Ives, Lawrence and Bui, Thuc and Habermann, Thomas and Collins, George and Marsden, David and Neilson, Jeffrey and Horn, Tim and Rock, Chris}, year={2023} }
 @article{zhang_carriere_amoako_rock_thielk_fletcher_horn_2023, title={Microstructure and Elevated Temperature Flexure Testing of Tungsten Produced by Electron Beam Additive Manufacturing}, volume={8}, ISSN={["1543-1851"]}, DOI={10.1007/s11837-023-06045-5}, abstractNote={AbstractDue to their superior high-temperature thermomechanical capabilities, sputter erosion durability, and excellent resistance to hydrogen isotopes, tungsten materials have garnered significant interest in fusion nuclear applications. However, low room-temperature ductility and complex machining strategies present significant challenges for traditional fabrication. Electron beam powder bed fusion (EB-PBF) shows promise in manufacturing pure tungsten via high thermal energy input, elevated build temperature, and a tightly controlled high-vacuum environment. This work explores the process, structure, and property relationship of pure tungsten fabricated by EB-PBF, where 99.8% relative density was achieved with reduced cracking by isolating the build substrate and optimizing the print parameter suite. Optical and electron imaging revealed that the microstructure contained equiaxed grains along the build direction, with subgrains present in all inspected grains. Flexural testing at ambient and elevated temperatures demonstrated high ductility at 900°C and flexural strength of 470 MPa at room temperature of additively manufactured tungsten.}, journal={JOM}, author={Zhang, Haozhi and Carriere, Paul R. and Amoako, Emmanuel D. and Rock, Chris D. and Thielk, Seiji U. and Fletcher, Colin G. and Horn, Timothy J.}, year={2023}, month={Aug} }
 @article{ovalle_rock_winkler_hartshorn_barr_cullom_tarafder_prost_white_anderson_et al._2023, title={Microstructure development and properties of micro-alloyed copper, Cu-0.3Zr-0.15Ag, produced by electron beam additive manufacturing}, volume={197}, ISSN={1044-5803}, url={http://dx.doi.org/10.1016/j.matchar.2023.112675}, DOI={10.1016/j.matchar.2023.112675}, abstractNote={A micro-alloyed copper powder, Cu-0.3Zr-0.15Ag wt%, was produced using gas atomization reaction synthesis. Zirconium was added to copper to sequester the oxygen present as copper oxide surface films on the powder particles. The as-received powders, as well as the intentionally oxidized powders were used to fabricate solid test articles by electron beam powder bed fusion additive manufacturing. Dense samples fabricated from as-received powder demonstrated nominal UTS, yield, and elongation values at 260 MPa, 150 MPa, and 34%, respectively. The average electrical conductivity of these samples was measured at 95% of the international annealed copper standard (IACS). Samples fabricated from the oxidized powder exhibited nominal UTS, yield, and elongation of 241 MPa, 146 MPa, and 43%, respectively, with an electrical conductivity of 95% IACS. During characterization, it was observed that, rather than forming nano-scale dispersoids, the Zirconia (ZrO2) appeared as discontinuous stringers in the metallographic cross-sections that crossed grain and melt pool boundaries. This was rationalized by tracing the presence of the micro-alloying addition of elemental zirconium, which was found to react with surface oxides dissociated in the melt pool to form ZrO2, which then solidified on the surface of the melt pool through an allotropic transformation to monoclinic ZrO2 in discontinuous films and spheroids ranging in size from nanometers to microns. This was confirmed by microscopic analysis of the tops of the melt pools. On subsequent melt passes, these ZrO2 structures were displaced and redistributed within the melt pool.}, journal={Materials Characterization}, publisher={Elsevier BV}, author={Ovalle, Denysse Gonzalez and Rock, Christopher and Winkler, Christopher and Hartshorn, Devin and Barr, Chris and Cullom, Tristan and Tarafder, Prithwish and Prost, Tim and White, Emma and Anderson, Iver and et al.}, year={2023}, month={Mar}, pages={112675} }
 @article{saptarshi_dejong_rock_anderson_napolitano_forrester_lapidus_kaoumi_horn_2022, title={Laser Powder Bed Fusion of ODS 14YWT from Gas Atomization Reaction Synthesis Precursor Powders}, volume={8}, ISSN={["1543-1851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85135355752&partnerID=MN8TOARS}, DOI={10.1007/s11837-022-05418-6}, abstractNote={AbstractLaser powder bed fusion (LPBF) additive manufacturing (AM) is a promising route for the fabrication of oxide dispersion strengthened (ODS) steels. In this study, 14YWT ferritic steel powders were produced by gas atomization reaction synthesis (GARS). The rapid solidification resulted in the formation of stable, Y-containing intermetallic Y2Fe17 on the interior of the powder and a stable Cr-rich oxide surface. The GARS powders were consolidated with LPBF. Process parameter maps identified a stable process window resulting in a relative density of 99.8%. Transmission electron microscopy and high-energy x-ray diffraction demonstrated that during LPBF, the stable phases in the powder dissociated in the liquid melt pool and reacted to form a high density (1.7 × 1020/m3) of homogeneously distributed Ti2Y2O7 pyrochlore dispersoids ranging from 17 to 57 nm. The use of GARS powder bypasses the mechanical alloying step typically required to produce ODS feedstock. Preliminary mechanical tests demonstrated an ultimate tensile and yield strength of 474 MPa and 312 MPa, respectively.}, journal={JOM}, author={Saptarshi, Sourabh and DeJong, Matthew and Rock, Christopher and Anderson, Iver and Napolitano, Ralph and Forrester, Jennifer and Lapidus, Saul and Kaoumi, Djamel and Horn, Timothy}, year={2022}, month={Aug} }
 @article{horn_rock_kaoumi_anderson_white_prost_rieken_saptarshi_schoell_dejong_et al._2022, title={Laser powder bed fusion additive manufacturing of oxide dispersion strengthened steel using gas atomized reaction synthesis powder}, volume={216}, ISSN={["1873-4197"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85127141491&partnerID=MN8TOARS}, DOI={10.1016/j.matdes.2022.110574}, abstractNote={Mechanically alloyed Fe-based alloys with oxide dispersion strengthening have largely dropped out of the marketplace due to high cost related to problems with complex and unreliable processing. Nevertheless, the desirable properties of oxide dispersion strengthened (ODS) steels have motivated research on alternate processing routes aimed at improving processing simplicity and reliability. Powders produced by gas atomization reaction synthesis (GARS) consist of stable Fe-Y intermetallic phases and a Cr surface oxide layer that acts as a chemical reservoir during solid-state processing and heat treatment to form a high density of nano-scale oxides. This research explores the use of Fe GARS powders, with 15 wt% Cr with micro-alloyed additions of 0.15 wt% Y and 0.10% Ti, in laser powder bed fusion (LPBF) additive manufacturing (AM), and evaluates the effectiveness of oxide dispersoid formation in the liquid melt pool. Additional oxygen was introduced by varying the LPBF chamber atmospheres using Ar, Ar + 1 wt% O, Ar + 5 wt% O, and air. Characterization of LPBF consolidated solids demonstrated the formation of a high density of nano-scale Y-Ti oxides in the build microstructures from the GARS precursor powders.}, journal={MATERIALS & DESIGN}, author={Horn, Timothy and Rock, Christopher and Kaoumi, Djamel and Anderson, Iver and White, Emma and Prost, Tim and Rieken, Joel and Saptarshi, Sourabh and Schoell, Ryan and DeJong, Matt and et al.}, year={2022}, month={Apr} }
 @article{zhang_darsell_wang_ma_grant_anderson_rieken_edwards_setyawan_horn_et al._2022, title={No ball milling nee de d: Alternative ODS steel manufacturing with gas atomization reaction synthesis (GARS) and friction-based processing}, volume={566}, ISSN={["1873-4820"]}, DOI={10.1016/j.jnucmat.2022.153768}, abstractNote={Oxide dispersion strengthened (ODS) steels are promising structural materials for future fusion reactors. The high-density (∼1023/m3) of highly stable Y-(Ti)-O nano-oxides provide high sink strength for radiation resistance and high-temperature (> 650 °C) creep strength. Concomitantly, helium management is enabled by trapping high density (∼1023/m3) of small (< 3 nm) helium bubbles in the vicinity of nano-oxides. However, conventional route of making ODS steels involves prolonged ball milling, canning, degassing, and laborious thermo-mechanical processing (TMP). Such route, especially the batch-by-batch ball milling step, faces persistent challenge with scalability and high costs. Gas atomization reaction synthesis (GARS) method has demonstrated the potential of making precursor ODS steel powders without ball milling, but the nano-oxide density was around 1021/m3 in the final consolidated form by conventional TMP. Taking advantage of GARS precursor powder, we use friction-based processing, including friction consolidation and extrusion, to manufacture ODS steel with further improved nano-oxide characteristics. Preliminary results showed that Y/Ti/O species were intimately mixed and rapidly reacted to form nano-oxides with a number density of ∼1022/m3.}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Zhang, D. and Darsell, J. T. and Wang, J. and Ma, X. and Grant, G. J. and Anderson, I. E. and Rieken, J. R. and Edwards, D. J. and Setyawan, W. and Horn, T. J. and et al.}, year={2022}, month={Aug} }
 @article{rock_tarafder_ives_horn_2021, title={Characterization of copper & stainless steel interface produced by electron beam powder bed fusion}, volume={212}, ISSN={["1873-4197"]}, DOI={10.1016/j.matdes.2021.110278}, abstractNote={Unalloyed copper (Cu) powder was deposited and melted onto a pre-existing stainless steel substrate using electron beam powder bed fusion (EB-PBF) additive manufacturing (AM) to form dense, bimetallic structures. The AM fabricated Cu was fully dense, and with strength properties consistent with recent reports on EB-PBF of Cu. The overall bimetallic structures exhibited total elongation of 25–35%, and was dominated by plastic deformation in the Cu region. Tensile failures were typically observed in the Cu portion of the bimetallic bodies demonstrating that the interface was not the source of mechanical failure. The interface region of the bimetallics contained areas of liquid phase separated Cu and Iron (Fe) + Chromium (Cr) rich regions resulting from a metastable miscibility gap in the Cu and Fe phase diagram. Metallurgical and mechanical examinations of the bimetallic structures showed the interface region transitions from an Fe rich mixture to a Cu rich mixture within a few AM layers.}, journal={MATERIALS & DESIGN}, author={Rock, Christopher and Tarafder, Prithwish and Ives, Lawrence and Horn, Timothy}, year={2021}, month={Dec} }
 @article{hankwitz_ledford_rock_o'dell_horn_2021, title={Electron Beam Melting of Niobium Alloys from Blended Powders}, volume={14}, ISSN={["1996-1944"]}, DOI={10.3390/ma14195536}, abstractNote={Niobium-based tungsten alloys are desirable for high-temperature structural applications yet are restricted in practice by limited room-temperature ductility and fabricability. Powder bed fusion additive manufacturing is one technology that could be leveraged to process alloys with limited ductility, without the need for pre-alloying. A custom electron beam powder bed fusion machine was used to demonstrate the processability of blended Nb-1Zr, Nb-10W-1Zr-0.1C, and Nb-20W-1Zr-0.1C powders, with resulting solid optical densities of 99+%. Ultimately, post-processing heat treatments were required to increase tungsten diffusion in niobium, as well as to attain satisfactory mechanical properties.}, number={19}, journal={MATERIALS}, author={Hankwitz, Jameson P. and Ledford, Christopher and Rock, Christopher and O'Dell, Scott and Horn, Timothy J.}, year={2021}, month={Oct} }
 @article{ellis_sprayberry_ledford_hankwitz_kirka_rock_horn_katoh_dehoff_2021, title={Processing of tungsten through electron beam melting *}, volume={555}, ISSN={["1873-4820"]}, DOI={10.1016/j.jnucmat.2021.153041}, abstractNote={Additive manufacturing (AM) presents a new design paradigm for the manufacture of engineering materials through the layer-by-layer approach combined with welding theory. In the instance of difficult to process materials such as tungsten and other refractory metals, AM offers an opportunity for radical redesign of critical components for next-generation energy technologies including fusion. In this work, electron beam powder bed fusion (EB-PBF) is applied to process pure tungsten to study the influence of process parameters on the defect density of the material. An in-situ image analysis algorithm is applied to pure tungsten for the first time, and is used to visualize the defect structure in AM tungsten. Finally, a cracking mechanism for AM tungsten is proposed, and suggestions for suppression of cracks in pure tungsten are offered.}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Ellis, Elizabeth A. I. and Sprayberry, Michael A. and Ledford, Christopher and Hankwitz, Jameson P. and Kirka, Michael M. and Rock, Chris D. and Horn, Timothy J. and Katoh, Yutai and Dehoff, Ryan R.}, year={2021}, month={Nov} }
 @article{tarafder_rock_horn_2021, title={Quasi-Static Tensile Properties of Unalloyed Copper Produced by Electron Beam Powder Bed Fusion Additive Manufacturing}, volume={14}, ISSN={["1996-1944"]}, DOI={10.3390/ma14112932}, abstractNote={Mechanical properties of powder bed fusion processed unalloyed copper are reported majorly in the as-fabricated condition, and the effect of post-processes, common to additive manufacturing, is not well documented. In this study, mechanical properties of unalloyed copper processed by electron beam powder bed fusion are characterized via room temperature quasi-static uniaxial tensile test and Vickers microhardness. Tensile samples were extracted both perpendicular and parallel to the build direction and assigned to three different conditions: as-fabricated, hot isostatic pressing (HIP), and vacuum annealing. In the as-fabricated condition, the highest UTS and lowest elongation were obtained in the samples oriented perpendicular to the build direction. These were observed to have clear trends between sample orientation caused primarily by the interdependencies between the epitaxial columnar grain morphology and dislocation movement during the tensile test. Texture was insignificant in the as-fabricated condition, and its effect on the mechanical properties was outweighed by the orientation anisotropy. The fractographs revealed a ductile mode of failure with varying dimple sizes where more shallow and finely spaced dimples were observed in the samples oriented perpendicular to the build direction. EDS maps reveal that grain boundary oxides coalesce and grow in HIP and vacuum-annealed specimens which are seen inside the ductile dimples and contribute to their increased ductility. Overall, for the post-process parameters chosen in this study, HIP was observed to slightly increase the sample’s density while vacuum annealing reduced the oxygen content in the specimens.}, number={11}, journal={MATERIALS}, author={Tarafder, Prithwish and Rock, Christopher and Horn, Timothy}, year={2021}, month={Jun} }
 @article{rock_ledford_garcia-avila_west_miller_pankow_dehoff_horn_2021, title={The Influence of Powder Reuse on the Properties of Nickel Super Alloy ATI 718 (TM) in Laser Powder Bed Fusion Additive Manufacturing}, volume={52}, ISSN={["1543-1916"]}, DOI={10.1007/s11663-020-02040-2}, number={2}, journal={METALLURGICAL AND MATERIALS TRANSACTIONS B-PROCESS METALLURGY AND MATERIALS PROCESSING SCIENCE}, author={Rock, Christopher and Ledford, Christopher and Garcia-Avila, Matias and West, Harvey and Miller, Victoria M. and Pankow, Mark and Dehoff, Ryan and Horn, Tim}, year={2021}, month={Apr}, pages={676–688} }
 @article{ives_bui_marsden_collins_horn_ledford_neilson_2020, title={Additive Manufacture of RF Loads for ITER}, DOI={10.1109/IVEC45766.2020.9520466}, abstractNote={The ITER fusion research facility will employ twenty-four, MW-class gyrotrons for electron cyclotron heating of the fusion plasma. Each of these gyrotron will require an RF load for commissioning and periodic maintenance and testing. These loads must dissipate approximately 1 MW of long pulse / continuous RF power with less than 0.5% of the power reflected back into the transmission line. This program is using additive manufacturing to reduce the cost and improve the performance.}, journal={2020 IEEE 21ST INTERNATIONAL CONFERENCE ON VACUUM ELECTRONICS (IVEC 2020)}, author={Ives, Lawerence and Bui, Thuc and Marsden, David and Collins, Geroge and Horn, Tim and Ledford, Chris and Neilson, Jeff}, year={2020}, pages={143–144} }
 @article{rock_lara-curzio_ellis_ledford_leonard_kannan_kirka_horn_2020, title={Additive Manufacturing of Pure Mo and Mo plus TiC MMC Alloy by Electron Beam Powder Bed Fusion}, volume={72}, ISSN={["1543-1851"]}, DOI={10.1007/s11837-020-04442-8}, abstractNote={A metal matrix composite powder of molybdenum (Mo) + TiC was produced by mechanical alloying (MA) and used in additive manufacturing by electron beam powder bed fusion along with pure Mo powder to form sandwich structures. The Mo + TiC solid layers formed mixed structures of Mo with discrete TiC particles, eutectic Mo + TiC, and Mo dendrites. Thermodynamic modeling showed that the system contained an invariant eutectic reaction in the composition range used and indicated that the system was highly sensitive to changes in composition and temperature.}, number={12}, journal={JOM}, author={Rock, Christopher and Lara-Curzio, Edgar and Ellis, Betsy and Ledford, Christopher and Leonard, Donovan N. and Kannan, Rangasayee and Kirka, Michael and Horn, Timothy}, year={2020}, month={Dec}, pages={4202–4213} }
 @article{jia_mehta_li_chowdhury_horn_xu_2021, title={Additive manufacturing of ZrB2-ZrSi2 ultra-high temperature ceramic composites using an electron beam melting process}, volume={47}, ISSN={["1873-3956"]}, DOI={10.1016/j.ceramint.2020.09.082}, abstractNote={Owing to their high melting points and ability to resist extreme thermal stresses, ultra-high temperature ceramics (UHTCs) are important materials for critical applications such as hypersonic flights, space re-entry vehicles, and rocket engines. Traditional manufacturing processes restrict the freedom to manufacture UHTCs with complex geometries due to the limitations of die and mold designs. Electron beam melting (EBM) is an established powder-bed layer-by-layer additive manufacturing (AM) process for metal parts. In this research, an effort was made to evaluate the feasibility of EBM for the AM fabrication of UHTC-based materials, and to investigate the microstructures of the fabricated materials under different processing conditions. A mathematical model was developed to simulate and optimize the processing parameters for the fabrication of ZrB2-30 vol% ZrSi2 UHTC using EBM. The simulation results were compared with experimental observations. For EBM fabrication of ZrB2-30 vol% ZrSi2 composites, the optimal processing parameters are beam power of 500 W with scanning speeds of 500, 750, and 1000 mm/s, and beam power of 1000 W with scanning speed of 1000 mm/s. This study demonstrates the potential for additive manufacturing of UHTCs with complex geometries by the EBM technique.}, number={2}, journal={CERAMICS INTERNATIONAL}, author={Jia, Yujun and Mehta, Shashvat Tejaskumar and Li, Ryan and Chowdhury, Md Atiqur Rahman and Horn, Timothy and Xu, Chengying}, year={2021}, month={Jan}, pages={2397–2405} }
 @article{rock_vadlakonda_figurskey_ledford_west_miller_pankow_daniels_horn_2020, title={Analysis of Self-Organized Patterned Surface Oxide Spots on Ejected Spatter Produced during Laser Powder Bed Fusion}, volume={35}, ISBN={2214-7810}, url={http://dx.doi.org/10.1016/j.addma.2020.101320}, DOI={10.1016/j.addma.2020.101320}, abstractNote={Spatter particles ejected from the melt pool after melting of 316 L stainless steel by laser powder bed fusion additive manufacturing (LPBF), were found to contain morphologies not observed in as-atomized 316 L powder. This spatter consisted of large, spherical particles, highly dendritic surfaces, particles with caps of accreted liquid, and agglomerations of multiple individual particles fixed together by liquid ligaments prior to solidification. The focus of this study is on an additional, unique spatter morphology consisting of larger, spherical particles with surface oxide spots exhibiting a wide distribution of surface configurations, including organized patterning. Spatter particles with organized surface oxide patterns were characterized for surface and internal particle features using multiple imaging techniques. The following observations are made: 1) spots resided at the spatter particle surface and did not significantly penetrate the interior, 2) the spot(s) were amorphous and rich in Silicon (Si)-Manganese (Mn)-Oxygen (O), 3) a two-part Chromium (Cr)-O rich layer exists between the particle and spot, 4) Cr-O rich morphological features were present at the top surface of the spots, 5) the spatter particle composition was consistent with 316 L but appeared to decrease in Si content into the spatter particle away from a spot, and 6) small Si-rich spherical particles existed within the spatter particle interior.}, journal={Additive Manufacturing}, publisher={Elsevier BV}, author={Rock, Christopher and Vadlakonda, Rashmi and Figurskey, Sullivan and Ledford, Christopher and West, Harvey and Miller, Victoria and Pankow, Mark and Daniels, Karen E. and Horn, Tim}, year={2020}, month={Oct}, pages={101320} }
 @article{nantista_gamzina_ledford_horn_carriere_frigola_2020, title={Design and Test of Copper Printed RF Cavities}, DOI={10.1109/IVEC45766.2020.9520624}, abstractNote={Additive manufacturing of high-quality copper using electron beam melting techniques has demonstrated significant progress toward suitability for production of vacuum electronics components. Additively manufactured low oxygen level copper wafers, as printed and annealed, have been tested in an RF cavity designed for surface resistivity measurements. Strings of coupled cavities for S-band and X-band traveling wave tubes have been designed for vertical additive manufacturing in powder bed systems, enabling significant cost reduction. The S-band RF cavity string design has been additively manufactured, processed and RF tested.}, journal={2020 IEEE 21ST INTERNATIONAL CONFERENCE ON VACUUM ELECTRONICS (IVEC 2020)}, author={Nantista, Christopher and Gamzina, Diana and Ledford, Christopher and Horn, Timothy and Carriere, Paul and Frigola, Pedro}, year={2020}, pages={149–150} }
 @article{du_yousefian_horn_muller_2020, title={Evaluation of Structural Anisotropy in a Porous Titanium Medium Mimicking Trabecular Bone Structure Using Mode-Converted Ultrasonic Scattering}, volume={67}, ISSN={["1525-8955"]}, DOI={10.1109/TUFFC.2019.2963162}, abstractNote={The mode-converted (longitudinal to transverse, L-T) ultrasonic scattering method was utilized to characterize the structural anisotropy of a phantom mimicking the structural properties of trabecular bone. The sample was fabricated using metal additive manufacturing from high-resolution computed tomography (CT) images of a sample of trabecular horse bone with strong anisotropy. Two focused transducers were used to perform the L-T ultrasonic measurements. A normal incidence transducer was used to transmit longitudinal ultrasonic waves into the sample, while the scattered transverse signals were received by an oblique incidence transducer. At multiple locations on the sample, four L-T measurements were performed by collecting ultrasonic scattering from four directions. The amplitude of the root mean square (rms) of the collected ultrasonic scattering signals was calculated for each L-T measurement. The ratios of rms amplitudes for L-T measurements in different directions were calculated to characterize the anisotropy of sample. The results show that the amplitude of L-T converted scattering is highly dependent on the direction of microstructural anisotropy. A strong anisotropy of the microstructure was observed, which coincides with simulation results previously published on the same structure as well as with the anisotropy estimated from the CT images. These results suggest the potential of mode-converted ultrasonic scattering methods to assess the anisotropy of materials with porous, complex structures, including trabecular bone.}, number={5}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, author={Du, Hualong and Yousefian, Omid and Horn, Timothy and Muller, Marie}, year={2020}, month={May}, pages={1017–1024} }
 @article{ledford_tung_rock_horn_2020, title={Real time monitoring of electron emissions during electron beam powder bed fusion for arbitrary geometries and toolpaths}, volume={34}, ISSN={["2214-7810"]}, DOI={10.1016/j.addma.2020.101365}, abstractNote={Real-time monitoring of electron emissions during the operable processing steps of electron beam powder bed fusion (EB-PBF), which typically include preheating, melting, and post-heating, provides a wealth of in-process data across multiple length scales. In this paper, we present a methodology for collecting both real-time beam positional data and electron emissions as a function of time for arbitrary component geometries and complex toolpaths. To demonstrate this, we collected these data during the melting steps of EB-PBF of pure copper and quantitatively compared electron images generated with this approach to both x-ray micro computed tomography (μCT) data and optical micrographs of the same specimens. These results show a strong mathematical correlation between the location of loss of signal events observed in electron images and observed defects in μCT. At the same time, the collection of beam positional information facilitates the calculation of beam velocities, and hence local energy inputs. We also demonstrate a to methodology visualize process data from a wide variety of sources and map these over the 3D geometries as a function of time and position and to link these spatiotemporal data to structure observed in the electron imaging and energy input maps. Ultimately, we have leveraged this new electron imaging approach to defect detection into a rudimentary control strategy to eliminate porosity in a copper sample.}, journal={ADDITIVE MANUFACTURING}, author={Ledford, Christopher and Tung, Mouda and Rock, Chris and Horn, Timothy}, year={2020}, month={Aug} }
 @article{ledford_rock_carriere_frigola_gamzina_horn_2019, title={Characteristics and Processing of Hydrogen-Treated Copper Powders for EB-PBF Additive Manufacturing}, volume={9}, ISSN={["2076-3417"]}, DOI={10.3390/app9193993}, abstractNote={The fabrication of high purity copper using additive manufacturing has proven difficult because of oxidation of the powder feedstock. Here, we present work on the hydrogen heat treatment of copper powders for electron beam powder bed fusion (EB-PBF), in order to enable the fabrication of high purity copper components for applications such as accelerator components and vacuum electronic devices. Copper powder with varying initial oxygen contents were hydrogen heat-treated and characterized for their chemistry, morphology, and microstructure. Higher initial oxygen content powders were found to not only reduce surface oxides, but also reduce oxides along the grain boundaries and form trapped H2O vapor inside the particles. The trapped H2O vapor was verified by thermogravimetric analysis (TGA) and residual gas analysis (RGA) while melting. The mechanism of the H2O vapor escaping the particles was determined by in-situ SEM heated stage experiments, where the particles were observed to crack along the grain boundaries. To determine the effect of the EB-PBF processing on the H2O vapor, the thermal simulation and the validation of single melt track width wafers were conducted along with melting single layer discs for chemistry analysis. A high speed video of the EB-PBF melting was performed in order to determine the effect of the trapped H2O vapor on the melt pool. Finally, solid samples were fabricated from hydrogen-treated copper powder, where the final oxygen content measured ~50 wt. ppm, with a minimal residue hydrogen content, indicating the complete removal of trapped H2O vapor from the solid parts.}, number={19}, journal={APPLIED SCIENCES-BASEL}, author={Ledford, Christopher and Rock, Christopher and Carriere, Paul and Frigola, Pedro and Gamzina, Diana and Horn, Timothy}, year={2019}, month={Oct} }
 @article{white_rinko_prost_horn_ledford_rock_anderson_2019, title={Processing of Alnico Magnets by Additive Manufacturing}, volume={9}, ISSN={["2076-3417"]}, DOI={10.3390/app9224843}, abstractNote={Permanent magnets without rare earth (RE) elements, such as alnico, will improve supply stability and potentially decrease permanent magnet cost, especially for traction drive motors and other increased temperature applications. Commercial alnico magnets with the highest energy product are produced by directional solidification (DS) to achieve a <001> columnar grain orientation followed by significant final machining, adding to the high cost. Additive manufacturing (AM) is an effective method to process near net-shape parts with minimal final machining of complex geometries. AM also, has potential for texture/grain orientation control and compositionally graded structures. This report describes fabrication of alnico magnets by AM using both laser engineered net shaping (LENS)/directed energy deposition (DED) and electron beam melting powder bed fusion (EBM/PBF). High pressure gas atomized (HPGA) pre-alloyed alnico powders, with high purity and sphericity, were built into cylindrical and rectangular samples, followed by magnetic annealing (MA) and a full heat treatment (FHT). The magnetic properties of these AM processed specimens were different from their cast and sintered counterparts of the same composition and show a great sensitivity to heat treatment. The AM process parameters used in this developmental study did not yet result in any preferred texture within the alnico AM builds. These findings demonstrate feasibility for near net-shape processing of alnico permanent magnets for use in next generation traction drive motors and other applications requiring increased operating temperatures and/or complex engineered part geometries, especially with further AM process development for texture control.}, number={22}, journal={APPLIED SCIENCES-BASEL}, author={White, Emma and Rinko, Emily and Prost, Timothy and Horn, Timothy and Ledford, Christopher and Rock, Christopher and Anderson, Iver}, year={2019}, month={Nov} }
 @article{mahbooba_thorsson_unosson_skoglund_west_horn_rock_vogli_harrysson_2018, title={Additive manufacturing of an iron-based bulk metallic glass larger than the critical casting thickness}, volume={11}, ISSN={["2352-9407"]}, DOI={10.1016/j.apmt.2018.02.011}, abstractNote={Fe-based bulk metallic glasses (BMG) are of increasing research interest, driven in part by a unique combination of mechanical, magnetic and chemical properties. However, the maximum thickness and geometry of BMGs achievable in traditional manufacturing processes is limited. This work examines the capabilities of laser based powder bed additive manufacturing (AM) to produce relatively large Fe-based bulk metallic glass specimens. AM fabricated specimens exceed the critical casting thickness of the material by a factor of 15 or more in all dimensions. Resulting microstructural and mechanical properties are reported. Despite decreasing quench effect with increasing build thickness, X-ray diffraction analysis suggests that a fully amorphous structure was maintained throughout the build. However, a low concentration of sparsely distributed nano-grain clusters was discovered using a high-resolution electron backscatter diffraction scan. The results pave the way for novel applications of metallic glasses achievable through appropriate material design and optimization of existing additive manufacturing processes.}, journal={APPLIED MATERIALS TODAY}, author={Mahbooba, Zaynab and Thorsson, Lena and Unosson, Mattias and Skoglund, Peter and West, Harvey and Horn, Timothy and Rock, Christopher and Vogli, Evelina and Harrysson, Ola}, year={2018}, month={Jun}, pages={264–269} }
 @inproceedings{horn_karakurt_ledford_gonzalez_gamzina_luhmann_lin_2018, title={Additively manufactured WR-10 copper waveguide}, DOI={10.1109/ivec.2018.8391526}, abstractNote={Direct additive manufacturing method utilizing electron beam melting techniques was employed to produce fully dense oxygen free copper W-band waveguides. By employing smaller copper powder, finer deposition layer, and spot-melting methodology surface roughness average has been reduced from 44 μm to 28 μm. A magnetically driven abrasive process was then employed to demonstrate further surface roughness average improvement of 5 μm. Initial RF test results on as-printed WR-10 waveguide confirm that surface post-processing will be essential to implementation of additive manufacturing techniques in vacuum electronics.}, booktitle={2018 ieee international vacuum electronics conference (ivec)}, author={Horn, Timothy and Karakurt, I. and Ledford, C. and Gonzalez, M. and Gamzina, D. and Luhmann, N. C. and Lin, L. W.}, year={2018}, pages={409–410} }
 @inproceedings{gamzina_luhmann_ledford_horn_karakaut_lin_frigola_2017, title={Additive vacuum electronics electron beam melting of copper}, DOI={10.1109/ivec.2017.8289495}, abstractNote={The construction of vacuum electronic devices is an artisan process; it requires extremes of high precision machining and assembly and the tolerances and feature sizes become more exacting as the frequency increases. Merging of copper additive manufacturing and electropolishing technologies will produce low-cost, high-throughput fabrication techniques for construction of fully integrated vacuum electronic devices. Technology demonstrations at two frequencies (S-Band and W-band) will address the demand for fast turnaround manufacturing of travelling wave tube amplifiers in legacy military systems as well as in the emerging high frequency applications.}, booktitle={2017 eighteenth international vacuum electronics conference (ivec)}, author={Gamzina, D. and Luhmann, N. C. and Ledford, C. and Horn, Timothy and Karakaut, I. and Lin, L. and Frigola, P.}, year={2017} }
 @article{schoenfeld-tacher_horn_scheviak_royal_hudson_2017, title={Evaluation of 3D Additively Manufactured Canine Brain Models for Teaching Veterinary Neuroanatomy}, volume={44}, ISSN={["1943-7218"]}, DOI={10.3138/jvme.0416-080r}, abstractNote={Physical specimens are essential to the teaching of veterinary anatomy. While fresh and fixed cadavers have long been the medium of choice, plastinated specimens have gained widespread acceptance as adjuncts to dissection materials. Even though the plastination process increases the durability of specimens, these are still derived from animal tissues and require periodic replacement if used by students on a regular basis. This study investigated the use of three-dimensional additively manufactured (3D AM) models (colloquially referred to as 3D-printed models) of the canine brain as a replacement for plastinated or formalin-fixed brains. The models investigated were built based on a micro-MRI of a single canine brain and have numerous practical advantages, such as durability, lower cost over time, and reduction of animal use. The effectiveness of the models was assessed by comparing performance among students who were instructed using either plastinated brains or 3D AM models. This study used propensity score matching to generate similar pairs of students. Pairings were based on gender and initial anatomy performance across two consecutive classes of first-year veterinary students. Students' performance on a practical neuroanatomy exam was compared, and no significant differences were found in scores based on the type of material (3D AM models or plastinated specimens) used for instruction. Students in both groups were equally able to identify neuroanatomical structures on cadaveric material, as well as respond to questions involving application of neuroanatomy knowledge. Therefore, we postulate that 3D AM canine brain models are an acceptable alternative to plastinated specimens in teaching veterinary neuroanatomy.}, number={4}, journal={JOURNAL OF VETERINARY MEDICAL EDUCATION}, publisher={University of Toronto Press Inc. (UTPress)}, author={Schoenfeld-Tacher, Regina M. and Horn, Timothy J. and Scheviak, Tyler A. and Royal, Kenneth D. and Hudson, Lola C.}, year={2017}, pages={612–619} }
 @article{mahbooba_west_harrysson_wojcieszynski_dehoff_nandwana_horn_2017, title={Effect of Hypoeutectic Boron Additions on the Grain Size and Mechanical Properties of Ti-6Al-4V Manufactured with Powder Bed Electron Beam Additive Manufacturing}, volume={69}, ISSN={["1543-1851"]}, DOI={10.1007/s11837-016-2210-9}, abstractNote={In additive manufacturing, microstructural control is feasible via processing parameter alteration. However, the window for parameter variation for certain materials, such as Ti-6Al-4V, is limited, and alternative methods must be employed to customize microstructures. Grain refinement and homogenization in cast titanium alloys has been demonstrated through the addition of hypoeutectic concentrations of boron. This work explores the influence of 0.00 wt.%, 0.25 wt.%, 0.50 wt.%, and 1.0 wt.% boron additions on the microstructure and bulk mechanical properties of Ti-6Al-4V samples fabricated in an Arcam A2 electron beam melting (EBM) system with commercial processing parameters for Ti-6Al-4V. Analyses of EBM fabricated Ti-6Al-4V + B indicate that the addition of 0.25–1.0 wt.% boron progressively refines the grain structure, and it improves hardness and elastic modulus. Despite a reduction in size, the β grain structure remained columnar as a result of directional heat transfer during EBM fabrication.}, number={3}, journal={JOM}, author={Mahbooba, Zaynab and West, Harvey and Harrysson, Ola and Wojcieszynski, Andrzej and Dehoff, Ryan and Nandwana, Peeyush and Horn, Timothy}, year={2017}, month={Mar}, pages={472–478} }
 @article{de luis balaguer_ramos-pezzotti_rahhal_melvin_johannes_horn_sozzani_2016, title={Multi-sample Arabidopsis Growth and Imaging Chamber (MAGIC) for long term imaging in the ZEISS Lightsheet Z.1}, volume={419}, ISSN={1095-564X}, DOI={10.1016/j.ydbio.2016.05.029}, abstractNote={Time-course imaging experiments on live organisms are critical for understanding the dynamics of growth and development. Light-sheet microscopy has advanced the field of long-term imaging of live specimens by significantly reducing photo-toxicity and allowing fast acquisition of three-dimensional data over time. However, current light-sheet technology does not allow the imaging of multiple plant specimens in parallel. To achieve higher throughput, we have developed a Multi-sample Arabidopsis Growth and Imaging Chamber (MAGIC) that provides near-physiological imaging conditions and allows high-throughput time-course imaging experiments in the ZEISS Lightsheet Z.1. Here, we illustrate MAGIC's imaging capabilities by following cell divisions, as an indicator of plant growth and development, over prolonged time periods. To automatically quantify the number of cell divisions in long-term experiments, we present a FIJI-based image processing pipeline. We demonstrate that plants imaged with our chamber undergo cell divisions for >16 times longer than those with the glass capillary system supplied by the ZEISS Z1.}, number={1}, journal={Developmental Biology}, author={Luis Balaguer, Maria Angels de and Ramos-Pezzotti, Marina and Rahhal, Morjan B. and Melvin, Charles E. and Johannes, Eva and Horn, Timothy J. and Sozzani, Rosangela}, year={2016}, month={Jan}, pages={19–25} }
 @article{harrysson_marcellin-little_horn_2015, title={Applications of Metal Additive Manufacturing in Veterinary Orthopedic Surgery}, volume={67}, ISSN={["1543-1851"]}, DOI={10.1007/s11837-015-1295-x}, number={3}, journal={JOM}, author={Harrysson, Ola L. A. and Marcellin-Little, Denis J. and Horn, Timothy J.}, year={2015}, month={Mar}, pages={647–654} }
 @article{horn_harrysson_west_little_marcellin-little_2014, title={Development of a patient-specific bone analog for the biomechanical evaluation of custom implants}, volume={20}, ISSN={["1758-7670"]}, DOI={10.1108/rpj-08-2012-0069}, abstractNote={
               Purpose
                – The aim of this study is to describe an improved experimental substrate for the mechanical testing of patient-specific implants fabricated using direct metal additive manufacturing processes. This method reduces variability and sample size requirements and addresses the importance of geometry at the bone/implant interface. 
            
            
               Design/methodology/approach
                – Short-fiber glass/resin materials for cortical bone and polyurethane foam materials for cancellous bone were evaluated using standard tensile coupons. A method for fabricating bone analogs with patient-specific geometries using rapid tooling is presented. Bone analogs of a canine radius were fabricated and compared to cadaveric specimens in several biomechanical tests as validation. 
            
            
               Findings
                – The analog materials exhibit a tensile modulus that falls within the range of expected values for cortical and cancellous bone. The tensile properties of the cortical bone analog vary with fiber loading. The canine radius models exhibited similar mechanical properties to the cadaveric specimens with a reduced variability. 
            
            
               Research limitations/implications
                – Additional replications involving different bone geometries, types of bone and/or implants are required for a full validation. Further, the materials used here are only intended to mimic the mechanical properties of bone on a macro scale within a relatively narrow range. These analog models have not been shown to address the complex microscopic or viscoelastic behavior of bone in the present study. 
            
            
               Originality/value
                – Scientific data on the formulation and fabrication of bone analogs are absent from the literature. The literature also lacks an experimental platform that matches patient-specific implant/bone geometries at the bone implant interface.
            }, number={1}, journal={RAPID PROTOTYPING JOURNAL}, author={Horn, Timothy J. and Harrysson, Ola L. A. and West, Harvey A., II and Little, Jeffrey P. and Marcellin-Little, Denis J.}, year={2014}, pages={41–49} }
 @article{frigola_harrysson_horn_west_aman_rigsbee_ramirez_murr_medina_wicker_et al._2014, title={Fabricating copper components with electron beam melting}, volume={172}, number={7}, journal={Advanced Materials & Processes}, author={Frigola, P. and Harrysson, O. A. and Horn, T. J. and West, H. A. and Aman, R. L. and Rigsbee, J. M. and Ramirez, D. A. and Murr, L. E. and Medina, F. and Wicker, R. B. and et al.}, year={2014}, pages={20–24} }