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President Obama recently announced plans to scrap NASA’s Constellation moon-landing project and to redirect funding toward programs that will lay the groundwork for a 2030 Mars expedition. This month JOM asks, what is the impact of the new priorities for NASA?
• The United States will lose its status as a worldwide leader of human spaceflight
• Scientific advancement will be stalled as R&D funding is redirected
• Commercial space launch services will be stimulated to fill the void left by NASA’s new priorities
• The U.S. space program will ultimately be better positioned for deep space exploration
The poll is conducted via the JOM Reader Zone of the TMS Discussion Board. |
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JOM DECEMBER 2009
VOLUME 61, NO.12
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![December 2009 Cover: This concentric ring pattern was produced with an aluminum mold using a semi-solidly processed metallic glass composite. The photo comes from the paper by Douglas C. Hofmann et al. describing a semi-solid forging process for metallic glass matrix composites. The article, accompanied by many color photos to illustrate the process, begins on page 11. [Click to enlarge]](http://www.tms.org/pubs/journals/jom/0912/cover-0912.gif)
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Nanomechanical Testing
Near-grain-boundary Transitions |
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Semi-solid Induction Forging of Metallic Glass Matrix Composites
By: Douglas C. Hofmann, Henry Kozachkov, Hesham E. Khalifa, Joseph P. Schramm, Marios D. Demetriou, Kenneth S. Vecchio, and William L. Johnson
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Structural Transitions and Local Deformation Processes at and Near Grain Boundaries: Shaping and Forming Committee
Mark Stoudt, National Institute of Standards and Technology
Novel Methods for Nanomechanics Testing: Nanomechanical Materials Behavior Committee
Xiaodong Li, University of South Carolina
Xinghang Zhang, Texas A&M University |
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Published monthly by The Minerals, Metals & Materials Society for its members, JOM is a technical journal devoted to exploring the many aspects of materials science and engineering.
Nanomechanical Testing: Challenges and Opportunities
[p. 18
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Author(s): Xiaodong Li and Xinghang Zhang
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Recent developments in science and engineering have enriched our capability to fabricate and control structures, materials, and devices on the scale of nanometers. The functionality and/or reliability of micro/nanodevices are often determined by the mechanical properties of individual nanostructures used to construct the devices. This commentary introduces three papers on the topic of nanomechanical testing, critical for the further development of high-quality micro/nanodevices.
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The In-situ Mechanical Testing of Nanoscale Single-crystalline Nanopillars
[p. 19
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Author(s): Julia R. Greer, Ju-Young Kim, and Michael J. Burek
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This article reviews recent studies on the mechanical properties of cylindrical metallic nanopillars subjected to uniaxial deformation. Remarkable strengths and very different mechanical properties arise due to the activation of unique deformation mechanisms operating in these nanoscale volumes. Effects of both size and microstructure are discussed.
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Tensile and Compressive Microspecimen Testing of Bulk Nanoporous Gold
[p. 26
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Author(s): T. John Balk, Chris Eberl, Ye Sun, Kevin J. Hemker, and Daniel S. Gianola
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Nanoporous gold (np-Au) is a macroscopically brittle material, which poses difficulties for tensile testing of bulk specimens. By combining a fabrication approach that minimizes cracking in bulk np-Au and a microspecimen test technique that permits small testing volumes, both tension and compression tests were performed on sub-millimeter gage thicknesses of np-Au. Compressive strength was higher than tensile strength, as would be expected for a brittle material, but all strength values were significantly lower than literature values for nanoindentation testing. Measured elastic modulus was nearly the same in tension and compression, and was much lower than Gibson-Ashby scaling relations would predict for porous gold with this density.
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High-temperature Nanoindentation: New Developments and Ongoing Challenges
[p. 32
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Author(s): Zhi Chao Duan and Andrea M. Hodge
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High-temperature or elevated-temperature nanoindentation testing presents an additional capability in nanoindentation techniques, which have demonstrated tremendous potential in the study of nanoscale mechanical behavior. However, to be able to conduct nanoindentation under relevant service temperatures and to gain a better understanding of the fundamental materials physics, high-temperature nanoindentation must overcome such technical issues as heat management, thermal drift, and sample oxidation. This article presents the current state and history of high-temperature nanoindentation with a focus on recent research topics and available testing systems.
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NEAR-GRAIN-BOUNDARY TRANSITIONS
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Structural Transitions and Local Deformation Processes at and Near Grain Boundaries
[p. 37
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Author(s): T.R. Bieler, R. Barabash, and S.W. Banovic
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This commentary introduces three papers that examine the heterogeneous structure, properties, and deformation characteristics near grain boundaries.
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Grain Boundary Complexions in Ceramics and Metals: An Overview
[p. 38
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Author(s): Shen J. Dillon, Martin P. Harmer, and Jian Luo
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The concepts of grain boundary phase transitions and complexions offer clues to resolve old problems such as abnormal grain growth and solidstate activated sintering as well as new opportunities for mechanism-informed materials design.
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Strain Heterogeneity and Damage Nucleation at Grain Boundaries during Monotonic Deformation in Commercial Purity Titanium
[p. 45
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Author(s): T.R. Bieler, M.A. Crimp, Y. Yang, L. Wang, P. Eisenlohr, D.E. Mason, W. Liu, and G.E. Ice
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Heterogeneous strain was analyzed in polycrystalline, commercial-purity titanium using many experimental techniques that provide information about microstructure, dislocation arrangement, grain orientation, orientation gradients, surface topography, and local strain gradients. The recrystallized microstructure with 50–200 μm grains was extensively characterized before and after deformation using 4-point bending to strains between 2% and 15%. Extremely heterogeneous deformation occurred along some grain boundaries, leading to orientation gradients exceeding 10° over 10–20 µm. Patches of highly characterized microstructure were modeled using crystal plasticity finite element (CPFE) analysis to simulate the deformation to evaluate the ability of the CPFE model to capture local deformation processes. Damage nucleation events were identified that are associated with twin interactions with grain boundaries. Progress toward identifying fracture initiation criteria based upon slip and twin interactions with grain boundaries is illustrated with related CPFE simulations of deformation in a TiAl alloy.
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Cyclic-loading-induced Accumulation of Geometrically Necessary Dislocations Near Grain Boundaries in an Ni-based Superalloy
[p. 53
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Author(s): E-Wen Huang, Rozaliya I. Barabash, Gene E. Ice, Wenjun Liu, Yee-Lang Liu, Ji-Jung Kai, and Peter K. Liaw
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In this study, the fatigue-induced microstructure produced in a nickel-based polycrystalline superalloy that was subjected to cyclic loading was characterized by polychromatic x-ray microdiffraction (PXM) together with in-situ neutron diffraction and transmission-electron microscopy (TEM). In-situ neutron-diffraction measurements reveal two distinct stages of the fatigue damage: cyclic hardening followed by cyclic softening. Three-dimensional spatially resolved PXM micro-Laue measurements find an increase in the density of geometrically necessary dislocations near the grain boundaries, which is accompanied by lattice rotations and grain subdivisions. The PXM results are in agreement with the in-situ neutron-diffraction and TEM results.
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TMS Ad Hoc Committee: Doing More to Recognize the Best and Brightest
[p. 10
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Author(s): Ray D. Peterson
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A TMS ad hoc committee has reviewed the society’s honors and awards system and has recommended some changes.
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Semi-solid Induction Forging of Metallic Glass Matrix Composites
[p. 11
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Author(s): Douglas C. Hofmann, Henry Kozachkov, Hesham E. Khalifa, Joseph P. Schramm, Marios D. Demetriou, Kenneth S. Vecchio, and William L. Johnson
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Metallic glasses have high strengths but are inherently brittle. To overcome this shortfall, metallic glass composites can be created by growing soft, crystalline particles in the glass to make it tougher. Processing these composites is difficult by any known method because they oxidize badly in open air and have high viscosity. This article describes a one-step casting process by which complex components can be made, opening the possibility for commercial and military hardware produced from high-strength toughened glassy composites.
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In the Final Analysis
[p. 02
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Author(s): James J. Robinson
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Selection of one’s professional affiliation is rarely a business decision based on who’s producing what commodities at the best prices. Rather, the decision to join and remain a member must appeal to both the head and the heart. In the Final Analysis offers a few thoughts on the benefits of TMS membership.
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News & Update
[p. 03
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Author(s): Anonymous
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Relive the Materials Science & Technology 2009 conference highlights through news stories and photos.
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Foundation News
[p. 07
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Author(s): Anonymous
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The TMS Foundation has a history of helping young members advance their professional careers. Read some of the ways in this issue of Foundation News.
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MemberNews
[p. 08
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Author(s): Francine Garrone
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Read about Akihisa Inoue, Acta Materialia Gold Medal Award winner, as well as about two new TMS member benefits. The featured member is Thomas Logue, who enjoys bicycle road racing.
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Meetings Calendar
[p. 59
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Author(s): Various
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A monthly round-up of soon-to-be-held meetings and upcoming calls for papers
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Materials Resource Center: Jobs, Consultants, Marketplace
[p. 60
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Author(s): Various
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Positions and services available.
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End Notes: "Symposium Honors the Diverse Contributions of Jim Evans"
[p. 64
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Author(s): Lynne Robinson
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A tricky aspect about organizing a symposium reflecting the contributions of James W. Evans is simply managing the broad range of topics that represents his body of work. The Jim Evans Honorary Symposium, slated for the TMS 2010 Annual Meeting in Seattle, Washington, February 14–18, will examine the wide-ranging technologies that have been investigated by Evans over the course of his career.
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![December 2009 Cover: This concentric ring pattern was produced with an aluminum mold using a semi-solidly processed metallic glass composite. The photo comes from the paper by Douglas C. Hofmann et al. describing a semi-solid forging process for metallic glass matrix composites. The article, accompanied by many color photos to illustrate the process, begins on page 11. [Click to enlarge]](http://www.tms.org/pubs/periodicals/journals/JOM/0912/cover-0912.gif)