@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{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{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} }
 @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{roy_atwater_youssef_ledford_scattergood_koch_2013, title={Studies on thermal stability, mechanical and electrical properties of nano crystalline Cu99.5Zr0.5 alloy}, volume={558}, ISSN={["0925-8388"]}, DOI={10.1016/j.jallcom.2012.11.004}, abstractNote={Cryogenic high energy ball milling was used to synthesize nanocrystalline Cu and Cu99.5Zr0.5 alloys by mechanical alloying and consolidation by hot pressing at 550 °C temperature. The grain size stability of nanocrystalline Cu is improved by the Zr addition. Microstructural characterization using X-ray diffraction and transmission electron microscopy provided evidence for the formation of a Cu–Zr alloy solid solution with nanocrystalline size after hot pressing. The alloy exhibited a higher hardness (3.31 GPa), and shear strength (550 MPa) than nano-crystalline pure Cu however, the electrical resistivity is increased in the alloy.}, journal={JOURNAL OF ALLOYS AND COMPOUNDS}, author={Roy, Debdas and Atwater, Mark A. and Youssef, Khaled and Ledford, John Christopher and Scattergood, Ronald O. and Koch, Carl C.}, year={2013}, month={May}, pages={44–49} }
 @inproceedings{ledford_gadfort_franzon_2012, title={An analysis of subthreshold SRAM bitcells for operation in low power RF-only technologies}, DOI={10.1109/subvt.2012.6404316}, abstractNote={Current RFID systems rely on the RF transciever to transmit information and convert RF power to DC to operate any integrated digital circuits. Research investigating the application of RF signals directly on digital CMOS circuits without RF-DC conversion is an emerging area for RFID technologies. One crucial digital circuit for most RFID systems is memory, needed for storing operational instructions and sampled data. An in-depth study and comparison of subthreshold SRAM bitcells has been conducted to analyze how such memories will function in a subthreshold RF-only regime without the need for RF-DC conversion. Several SRAM cells were chosen for conversion into the RF-only family and measured against several metrics, including highest performance at lowest operating voltage, power consumption, and static noise margins (SNM). Including RF supply transistors, an 18-T subthreshold RF-only bitcell is proposed, capable of operating at a data rate of 100 kHz at VRF of 200mVRMS.}, booktitle={2012 IEEE subthreshold microelectronics conference (SUBVT)}, author={Ledford, J. and Gadfort, P. and Franzon, Paul}, year={2012} }