Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 60, Number 11
Friday–Saturday, October 16–17, 2015; Tempe, Arizona
Session E5: Materials IV: Mechanical Properties and Alloys |
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Chair: Carmen Menoni, Colorado State University Room: MU220 |
Friday, October 16, 2015 3:17PM - 3:41PM |
E5.00001: Temperature-dependent modeling of grain boundary energy anisotropy and applications to interface morphology} Invited Speaker: Brandon Runnels Grain boundaries (GBs) in polycrystalline materials are unique defects that exhibit a strong energetic dependence on relative crystallographic orientation. This behavior, referred to as grain boundary anisotropy, dominates many mesoscopic mechanisms such as solidification, recrystallization, grain boundary migration, and severe plastic deformation. To this end, it is of great importance to understand and predictively model grain boundary energy. An analytical model is presented in this work that computes GB energy quickly and predictively for a wide range of materials and crystal structures for all GB configurations in the five-dimensional space of crystallographic orientation pairs. This forms the basis for a fully general, temperature-dependent energetic grain boundary energy model, and it is demonstrated by comparison with a wide selection of molecular dynamics energy data for FCC and BCC tilt and twist boundaries that the model accurately reproduces the energy landscape using a consistent set of three material parameters. By the application of a relaxation method, it is then demonstrated that the model can be extended from planar GBs to GBs with complex morphology. Application of this method shows that GB facet patterns arise as energy minimizers in a wide range of orientations, and the model predictions are validated by MD and experimental observations. Additionally, it is shown that the model captures the temperature-dependence of the GB energy by reproducing experimentally observed temperature-dependent faceting transitions. The talk concludes with a brief discussion of current challenges, future directions, and direct applications of the model. [Preview Abstract] |
Friday, October 16, 2015 3:41PM - 3:53PM |
E5.00002: Using EBSD for Strain Analysis in Laser Shocked Ta Samples Kameron Hansen, Greg Randall, Don Wall, Brian Jackson A recent comparison of high-pressure, high-strain rate compression experiments with simulations (H.S. Park et al., Phys. Rev. Lett., 2015) indicates that a metal's initial dislocation density is a key factor in determining its strength at extreme strain rate and pressure. However, mapping the dislocation density in these materials, specifically after they have been formed into experimental targets, has not been performed. We use electron backscatter diffraction (EBSD) to develop a method to characterize strain and dislocation density in annealed, coined, and shocked polycrystalline tantalum samples. In this initial work, we use linescans across grain boundaries to evaluate the resolution of our tungsten filament electron microscope and Oxford EBSD camera/EBSD acquisition software. Furthermore, we measure dislocation density using both Hough transform and cross-correlation strain analysis algorithms, and form misorientation maps (corresponding to dislocation density). [Preview Abstract] |
Friday, October 16, 2015 3:53PM - 4:05PM |
E5.00003: Wang Landau for Real Alloys Derek Ostrom, Lance Nelson, Gus Hart Cluster Expansions are effective in providing fast Hamiltonians for modeling alloys.This enables us to find transition temperatures via Monte Carlo modeling. These Monte Carlo simulations require many tunable parameters that affect the results in non-intuitive ways. A new method proposed by Wang and Landau gives us a much simpler recipe for computing thermodynamic quantities. We demonstrate the power of this approach using the realistic example of the AgPd alloy. [Preview Abstract] |
Friday, October 16, 2015 4:05PM - 4:17PM |
E5.00004: A high-throughput search for new ternary superalloys Chandramouli Nyshadham, Jacob Hansen, Corey Oses, Stefano Curtarolo, Gus Hart In 2006 an unexpected new superalloy, Co$_{3}$[Al, W], was discovered[1]. The new alloy is a cobalt-based alloy, in contrast to conventional superalloys which are nickel-based. Inspired by this new discovery, we performed first-principles calculations to explore many more potential superalloys. Searching through 2224 ternary metallic systems of the form A$_{3}$[B$_{0.5}$C$_{0.5}$], where A = Ni/Co/Fe and [B, C] = all binary combinations of 40 different elements chosen from the periodic table, we found 175 new systems that are better than the Co$_{3}$[Al, W] superalloy. 75 of these systems are brand new--- They have never been reported in experimental literature. Our results show that, in general, 1) Ni-based superalloys are more thermodynamically stable than Co- or Fe-based ones; 2) Co-based alloys have better bulk modulus than Ni- or Fe-based ones. Our results are also in agreement with the current experimental literature where they overlap. The 75 new candidates found in this work contain potential superalloys and are good candidates for performing further experiments.\\ {\tiny \raggedright {\footnotesize [1] Sato $et$, $al$., ``Cobalt-base high temperature alloys. Science 2006; 312 (5770):90-1."} \\ } [Preview Abstract] |
Friday, October 16, 2015 4:17PM - 4:29PM |
E5.00005: In situ Observation of Ag Nanoparticles Catalyzed Oxidation of Carbon Nanotubes in an Aberration-corrected Environmental TEM Datong Yuchi, Yonghai Yue, Jingyue Liu The emission of soot or particulate matter formed during combustion of carbonaceous fuels is the major source of air pollution. Catalytic oxidation of soot in the exhaust gas is critical to reducing the negative environmental impact of power sources. The fundamental understanding of metal nanoparticle catalyzed oxidation processes of carbon materials is of interest. We report here the \textit{in situ} investigation of Ag nanoparticle catalyzed oxidation of multi-wall carbon nanotubes (MW-CNTs) inside an aberration-corrected environmental TEM with the goal of probing the nature of the active sites, the catalytic processes and the atomic scale structural evolutions of the Ag nanoparticles and the MW-CNTs. It was found that the Ag nanoparticles initiated the oxidation of MW-CNTs at a temperature of about 250 \textdegree C while without the use of Ag nanoparticle the MW-CNTs did not oxidize until well above 500 \textdegree C. Atomic scale information on the Ag nanoparticle catalyzed oxidation processes of MW-CNTs has been obtained and a model for the catalytic oxidation process was proposed. [Preview Abstract] |
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