Publications

  • Chen-Nan Sun, Mool C. Gupta, Karen M. B. Taminger
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    ABSTRACT: Electron beam sintering of ultra-high-temperature ceramic material of zirconium diboride (ZrB2) was successfully carried out. Scanning electron microscopy images showed that the sintered layer had smooth surface morphology. Significant grain growth was observed by increasing the electron beam current density. More uniform and finer microstructures could be obtained using high beam currents and short dwell times. Chemical composition analysis confirmed that sintering in a vacuum environment could minimize boron loss. X-ray diffraction results revealed that the sintered layer mainly preserved the crystalline phase from the starting powder.
    Journal of the American Ceramic Society 04/2010; 93(9):2484 - 2486. · 2.11 Impact Factor
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    W. J. Seufzer, K. M. Taminger
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    ABSTRACT: Engineering a closed-loop control system for an electron beam welder for additive manufacturing is challenging. For earth and space based applications, components must work in a vacuum and optical components must be protected from becoming occluded with metal vapor. For extraterrestrial applications added components increase launch weight and increase complexity. Here we present three different control methods for electron beam free form fabrication. A relatively simple coarse feedback control method is introduced that couples path planning and electron beam parameter controls into the build process to increase flexibility and improve build quality. The different approaches may be applied separately or together to provide enhanced EBF3 system performance.
    07/2007;
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    ABSTRACT: Previous NASA work has included fabrication and modeling of hybrid composite (HC) specimens with embedded Nitinol ribbon actuators and thermomechanical testing of the constituents. The Nitinol tensile behavior depended significantly on the thermomechanical condition (TMC). A Nitinol microstructure/mechanical property characterization was conducted on four TMCs. Differential scanning calorimetry and x-ray diffraction were used to rationalize the microstructures present. Tensile tests determined the effect of TMC on the Nitinol tensile behavior and stress state of the microstructure. Three TMCs showed typical shape memory behavior. The TMC that simulated the HC autoclave process on the actuator resulted in an irreversible microstructure. The microstructural constituents and their stress states probably govern the Nitinol stress–strain behavior. The critical stress to achieve an initial stress plateau was dependent on the amount and stress state of R-phase present in the initial microstructure. Thus, prior TMC critically affects the Nitinol tensile behavior. Numerical model inputs must therefore account for these effects on the Nitinol actuator.
    Smart Materials and Structures 02/2006; 15(2):485. · 2.02 Impact Factor
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    ABSTRACT: Manufacturing of structural metal parts directly from computer aided design (CAD) data has been investigated by numerous researchers over the past decade. Researchers at NASA Langley Research Center are developing a new solid freeform fabrication process, electron beam freeform fabrication (EBF 3), as a rapid metal deposition process that works efficiently with a variety of weldable alloys. EBF 3 deposits of 2219 aluminium and Ti-6Al-4V have exhibited a range of grain morphologies depending upon the deposition parameters. These materials have exhibited excellent tensile properties comparable to typical handbook data for wrought plate product after post-processing heat treatments. The EBF 3 process is capable of bulk metal deposition at deposition rates in excess of 2500 cm 3 /hr (150 in 3 /hr) or finer detail at lower deposition rates, depending upon the desired application. This process offers the potential for rapidly adding structural details to simpler cast or forged structures rather than the conventional approach of machining large volumes of chips to produce a monolithic metallic structure. Selective addition of metal onto simpler blanks of material can have a significant effect on lead time reduction and lower material and machining costs.
    01/2006;
  • Karen M. B. Taminger, Robert A. Hafley, Marcia S. Domack
    Materials Science Forum - MATER SCI FORUM. 01/2006;
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    ABSTRACT: Electron beam freeform fabrication (EBF3) parts exhibit a ridged surface finish typical of many layer-additive processes. Thus, post-processing is required to produce a net shape with a smooth surface finish. High speed milling, wire electrical discharge machining (EDM), electron beam glazing, and glass bead blasting were performed on EBF(3)-built 2219 aluminum alloy parts to reduce or eliminate the ridged surface features. Surface roughness, surface residual stress state, and microstructural characteristics were examined for each of the different surface treatments to assess the quality and effect of the surface treatments on the underlying material. The analysis evaluated the effectiveness of the different surface finishing techniques for achieving a smooth surface finish on an electron beam freeform fabricated part.
    07/2004;
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    ABSTRACT: A study was conducted to evaluate the relative significance of input parameters on Ti- 6A1-4V deposits produced by an electron beam freeform fabrication process under development at the NASA Langley Research Center. Five input parameters where chosen (beam voltage beam current, translation speed, wire feed rate, and beam focus), and a design of experiments (DOE) approach was used to develop a set of 16 experiments to evaluate the relative importance of these parameters on the resulting deposits. Both single-bead and multi-bead stacks were fabricated using 16 combinations, and the resulting heights and widths of the stack deposits were measured. The resulting microstructures were also characterized to determine the impact of these parameters on the size of the melt pool and heat affected zone. The relative importance of each input parameter on the height and width of the multi-bead stacks will be discussed.
    07/2004;
  • J. K. Watson, K. M. Taminger, R. A. Hafley
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    ABSTRACT: NASA's Langley Research Center and Johnson Space Center are developing a solid freeform fabrication system utilizing an electron beam energy source and wire feedstock. This system will serve as a testbed for exploring the influence of gravitational acceleration on the deposition process and will be a simplified prototype for future systems that may be deployed during long-duration space missions for assembly, fabrication, and production of structural and mechanical replacement components. Critical attributes for this system are compactness, minimal mass, efficiency in use of feedstock material, energy use efficiency, and safety. The use of a low-voltage (<15kV) electron beam energy source will reduce radiation so that massive shielding is not required to protect adjacent personnel. Feedstock efficiency will be optimized by use of wire, and energy use efficiency will be achieved by use of the electron beam energy source. This system will be evaluated in a microgravity environment using the NASA KC-135A aircraft.
    09/2002;
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    Karen M. B. Taminger, Robert A. Hafley
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    ABSTRACT: Researchers at NASA Langley Research Center are developing a new electron beam freeform fabrication (EB F3) technique to fabricate metal parts. This process introduces metal wire into a molten pool created by a focused electron beam. Potential aerospace applications for this technology include ground-based fabrication of airframe structures and on-orbit construction and repair of space components and structures. Processing windows for reliably producing high quality 2219 aluminum parts using the EB F3 technique are being defined. The effects of translation speed, wire feed rate, and beam power on the resulting microstructures and mechanical properties are explored. Tensile properties (ultimate tensile strength, yield strength, and elongation) show little effect over the range of processing conditions tested. Basic processing-microstructure-property correlations are drawn for the EB F3 process.
    09/2002;
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    Karen M. B. Taminger, Robert A. Hafley, Dennis L. Dicus
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    ABSTRACT: The emerging class of direct manufacturing processes known as Solid Freeform Fabrication (SFF) employs a focused energy beam and metal feedstock to build structural parts directly from computer aided design (CAD) data. Some variations on existing SFF techniques have potential for application in space for a variety of different missions. This paper will focus on three different applications ranging from near to far term to demonstrate the widespread potential of this technology for space-based applications. One application is the on-orbit construction of large space structures, on the order of tens of meters to a kilometer in size. Such structures are too large to launch intact even in a deployable design; their extreme size necessitates assembly or erection of such structures in space. A low-earth orbiting satellite with a SFF system employing a high-energy beam for high deposition rates could be employed to construct large space structures using feedstock launched from Earth. A second potential application is a small, multifunctional system that could be used by astronauts on long-duration human exploration missions to manufacture spare parts. Supportability of human exploration missions is essential, and a SFF system would provide flexibility in the ability to repair or fabricate any part that may be damaged or broken during the mission. The system envisioned would also have machining and welding capabilities to increase its utility on a mission where mass and volume are extremely limited. A third example of an SFF application in space is a miniaturized automated system for structural health monitoring and repair. If damage is detected using a low power beam scan, the beam power can be increased to perform repairs within the spacecraft or satellite structure without t...
    07/2002;
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    ABSTRACT: Shape memory alloys (SMAs) have enormous potential for a wide variety of applications. A large body of work exists on the characterization of the microstructure and stress-strain behavior of these alloys, Nitinol (NiTi) in particular. However, many attributes of these materials are yet to be fully understood.
    05/2002;
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    ABSTRACT: Shape memory alloys (SMAs) have enormous potential for a wide variety of applications. A large body of work exists on the characterization of the microstructure and stress-strain behavior of these alloys, Nitinol (NiTi) in particular. However, many attributes of these materials are yet to be fully understood. Previous work at NASA Langley Research Center (LaRC) has included fabrication of hybrid composite specimens with embedded Nitinol actuators and modeling of their thermomechanical behavior. An intensive characterization effort has been undertaken to facilitate fundamental understanding of this alloy and to promote implementation of Nitinol in aerospace applications. Previous work revealed attributes of the Nitinol ribbon that were not easily rationalized with existing data in the literature. In particular, tensile behavior at ambient temperature showed significant dependence on the thermomechanical history prior to testing. The present work is focused on characterizing differences in the microstructure of Nitinol ribbons exposed to four different thermomechanical histories and correlation of the microstructure with tensile properties. Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) analysis were employed to rationalize the microstructures present after exposure to various thermomechanical histories. Three of the Nitinol ribbon conditions were reversible upon heating (in the DSC) through the reverse transformation temperature (A f) to transform the microstructure to austenite. However, the prior thermomechanical conditioning for the Nitinol ribbon that reflected the entire fabrication procedure (4% thermal cycle condition) was found to have an irreversible effect on the microstructure, as it remained unchanged after repeated complete thermal cycles. Tensile tests were conducted to determine the effect of prior thermomechancial conditioning on both the tensile behavior of the Nitinol ribbons and the stress state of the microstructure. The stress-strain behavior of the Nitinol actuators appears to be governed by the interplay between two major variables: namely, microstructural constituents such as the R-phase and the martensite; and the stress state of these constituents (whether twinned with low residual stresses, or detwinned with high residual stresses). The most significant difference in the stress-strain behavior of the four conditions, the critical stress required to achieve an initial stress plateau, was found to depend on both the amount and stress state (twinned or detwinned) of R-phase present in the initial microstructure. Thus, the effect of prior thermomechanical processing is critical to the resulting tensile behavior of the Nitinol actuator. For numerical modeling inputs one must take into account the entire fabrication process on the Nitinol actuator.
    Proc SPIE 04/2002; 4699:4699-45.
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    Karthik Nagarathnam, Karen M. B. Taminger
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    ABSTRACT: . Lasers are useful for performing operations such as joining, machining, built-up freeform fabrication, shock processing, and surface treatments. These attributes are attractive for the supportability of longer-term missions in space due to the multi-functionality of a single tool and the variety of materials that can be processed. However, current laser technology also has drawbacks for space-based applications, specifically size, power efficiency, lack of robustness, and problems processing highly reflective materials. A review of recent laser developments will be used to show how these issues may be reduced and indicate where further improvement is necessary to realize a laser-based materials processing capability in space. The broad utility of laser beams in synthesizing various classes of engineering materials will be illustrated using state-of-the art processing maps for select lightweight alloys typically found on spacecraft. With the advent of recent breakthroughs in diode-pum...
    04/2001;
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    Karen M. B. Taminger, John A. Wagner, W. Barry Lisagor
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    ABSTRACT: As a result of high localized plastic deformation experienced during proof testing in an International Space Station connecting module, a study was undertaken to determine the deformation response of a 2219-T851 roll forging. After prestraining 2219-T851 Al specimens to simulate strains observed during the proof testing, creep tests were conducted in the temperature range from ambient temperature to 107C (225F) at stress levels approaching the ultimate tensile strength of 2219-T851 Al. Strain-time histories and strain rate responses were examined. The strain rate response was extremely high initially, but decayed rapidly, spanning as much as five orders of magnitude during primary creep. Select specimens were subjected to incremental step loading and exhibited initial creep rates of similar magnitude for each load step. Although the creep rates decreased quickly at all loads, the creep rates dropped faster and reached lower strain rate levels for lower applied loads. The initial creep ...
    06/2000;
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    ABSTRACT: NASA's Langley Research Center and Johnson Space Center are developing a solid freeform fabrication system utilizing an electron beam energy source and wire feedstock. This system will serve as a testbed for exploring the influence of gravitational acceleration on the deposition process and will be a simplified prototype for future systems that may be deployed during long-duration space missions for assembly, fabrication, and production of structural and mechanical replacement components. Critical attributes for this system are compactness, minimal mass, efficiency in use of feedstock material, energy use efficiency, and safety. The use of a low-voltage (
  • Source
    Karen M. B. Taminger, Robert A. Hafley
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    ABSTRACT: Manufacturing of structural metal parts directly from computer aided design (CAD) data has been investigated by numerous researchers over the past decade. Researchers at NASA Langley Research Center are developing a new solid freeform fabrication process, electron beam freeform fabrication (EBF 3 ), as a rapid metal deposition process that works efficiently with a variety of weldable alloys. The EBF 3 process introduces metal wire feedstock into a molten pool that is created and sustained using a focused electron beam in a vacuum environment. Thus far, this technique has been demonstrated on aluminum and titanium alloys of interest for aerospace structural applications; nickel and ferrous based alloys are also planned. Deposits resulting from 2219 aluminum demonstrations have exhibited a range of grain morphologies depending upon the deposition parameters. These materials have exhibited excellent tensile properties comparable to typical handbook data for wrought plate product after post-processing heat treatments. The EBF3 process is capable of bulk metal deposition at deposition rates in excess of 2500 cm3/hr (150 in3/hr) or finer detail at lower deposition rates, depending upon the desired application. This process offers the potential for rapidly adding structural details to simpler cast or forged structures rather than the conventional approach of machining large volumes of chips to produce a monolithic metallic structure. Selective addition of metal onto simpler blanks of material can have a significant effect on lead time reduction and lower material and machining costs. Background

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