@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={Abstract Due 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{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{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} }