Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session H28: Focus Session: Metallic Glasses and Liquids I |
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Sponsoring Units: DMP Chair: Despina Louca, University of Virginia Room: LACC 506 |
Tuesday, March 22, 2005 8:00AM - 8:36AM |
H28.00001: Structural Amorphous Metals – Amorphous Steels and Ultra-Strong Light Metals Invited Speaker: Amorphous metals are multicomponent alloys and are naturally complex. In recent years, significant progress in the design of bulk amorphous metals and fundamental understanding of the amorphous state has been achieved. In this talk, we will report current interdisciplinary studies of structural amorphous metals, with a focus on the synthesis, properties, and basic knowledge. Recent results on amorphous steels and amorphous light-metals will be highlighted. * Work in collaborations with Professor Gary Shiflet, Drs. V. Ponnambalam, F. Q. Guo, J. Wang, and X. F. Gu. Research supported by DAPA, ONR, and AFOSR. [Preview Abstract] |
Tuesday, March 22, 2005 8:36AM - 9:12AM |
H28.00002: Thermodynamics and Statistical Mechanics of Bulk Metallic Glasses Invited Speaker: A survey of the mechanical, rheological, and thermodynamic properties of bulk metallic glasses and glass forming liquids will be presented. The experimental data reveal striking systematic correlations among linear elastic constants, plastic yielding of the glass and its dependence on temperature, the glass transition temperature, and rheological properties of the glass forming liquid. A Cooperative Shear Model will be presented while predicts that physically relevant features of the Potential Energy Landscape of the glass/liquid obey simple scaling relations. The model predicts the yield criterion and its dependence on temperature in the glass. It also leads to natural expressions for the Newtonian and Non-Newtonian viscosity law for the liquids, as well as the fragility of the liquid. The model is found to be in remarkable agreement with a variety of experimental observations including variations in ductility and toughness among metallic glasses. It predicts that all metallic glasses exhibit universal behavior based on a small number of measurable parameters. [Preview Abstract] |
Tuesday, March 22, 2005 9:12AM - 9:48AM |
H28.00003: Medium-Range Structure in Al-based Amorphous Metals from Fluctuation Electron Microscopy Invited Speaker: High-Al content amorphous metals formed by rapid quenching devitrify to nanometer-sized Al nanocrystals in an amorphous matrix at remarkably high nanocrystal density ($>$10$^{20}$ m$^{-3})$. We have found nanoscale, Al-like order in rapidly quenched amorphous Al$_{92}$Sm$_{8}$ using fluctuation electron microscopy, a quantitative TEM technique uniquely sensitive to nanoscale order in amorphous materials. This order is not found in Al$_{92}$Sm$_{8}$ amorphized by mechanical deformation, which also does not devitrify to the nanocrystal / matrix microstructure. The nanoscale order in the rapid-quenched samples is reduced by thermal annealing, suggesting that fluctuation microscopy is measuring sub-critical Al clusters retained during the quench. [Preview Abstract] |
Tuesday, March 22, 2005 9:48AM - 10:00AM |
H28.00004: Bulk metallic glass formation in Zr$_{65}$Cu$_{27}$Ti$_{8}$ Alloys Y. T. Shen, L. Q. Xing, K. F. Kelton Although bulk glass (BMG) formation has been reported in Cu- rich Cu-Zr alloys, it has not been observed in the Zr-rich alloys. Here, we report that the substitution of Ti for Cu in Zr$_{65}$Cu$_{35}$ alloys dramatically improves glass formation, giving Zr$_{65}$Cu$_{27}$Ti$_{8}$ bulk metallic glasses with diameters up to 1mm by suction casting. However, the onset crystallization temperatures and the widths of the supercooled liquid region are reduced with the introduction of Ti, due to the formation of a metastable icosahedral quasicrystal at lower crystallization temperatures in the glasses made with Ti. These observations suggest the formation of icosahedral short-range order in the supercooled liquid alloy, which increases the nucleation barrier for the Zr$_{2} $Cu phase during the quench and makes glass formation easier. This is supported by results from recent in-situ measurements of the supercooled liquid structures of Zr-Ti-Cu-Ni-Al alloys. [Preview Abstract] |
Tuesday, March 22, 2005 10:00AM - 10:12AM |
H28.00005: Effect of Icosahedral Short-range Order on the Undercoolability of Ti-Zr-Ni Liquid Alloys G. W. Lee*, A. K. Gangopadhyay, K. F. Kelton, R. W. Hyers, T. J. Rathz, J. R. Rogers, A. I. Goldman Icosahedral short-range order (ISRO) in metallic liquids leads to a high nucleation barrier for crystal phases and is, therefore, an important factor for determining the amount of undercooling. High energy (125 keV) x-ray diffraction studies were made on electrostatically levitated Ti-Zr-Ni liquids that form the solid solution phase, $\beta$(Ti/Zr), the icosahedral quasicrystal (i-phase), and a polytetrahedral C14 Laves phase to correlate undercooling with the short-range order in the liquid phase. The undercoolability increases with increasing Ni concentration for liquids that form the $\beta$(Ti/Zr) and C14 phases. The maximum ISRO and minimum undercooling is found for the liquid that crystallizes to the i-phase. These data are presented and discussed in terms of a local cluster model for the liquid. [Preview Abstract] |
Tuesday, March 22, 2005 10:12AM - 10:24AM |
H28.00006: Role of Icosahedral Short-range-order in Undercooled Liquids of Zr-Ti-Cu-Ni-Al Alloys on Bulk Metallic Glass Formation A. K. Gangopadhyay, G. W. Lee, T. H. Kim, K. F. Kelton, R. C. Bradshaw, R. W. Hyers, T. J. Rathz, J. R. Rogers, B. Sieve, A. I. Goldman The addition of a few percent of some elements often significantly improves the glass formability of bulk metallic glasses (BMG); Zr$_{62-x}$Ti$_{x}$Ni$_{20}$Cu$_{10}$Al$_{8}$ (x $<$ 8) is one such example. The role of Ti addition on short- range-order in this alloy system was studied by in-situ x-ray diffraction on levitated droplets of stable and undercooled liquids with high energy (125 keV) synchrotron x-rays on the beamline 6ID-D of the MU-CAT facility at the Advanced Photon Source (APS) at the Argonne National Lab, using the recently developed BESL (beamline electrostatic levitation) technique. The short-range-order of the liquid was found to be dominantly icosahedral (ISRO), stabilized further by Ti addition, indicating an important role of ISRO on BMG formation. Additional effects of Ti addition on dynamical properties of the liquid (e.g. viscosity) will be reported and the effects of ISRO and viscosity on nucleation and glass formation will be discussed. [Preview Abstract] |
Tuesday, March 22, 2005 10:24AM - 10:36AM |
H28.00007: Direct observation of enhanced residual thermal energy coupling to solids in femtosecond laser ablation Anatoliy Vorobyev , Chunlei Guo We perform the first direct measurement of the thermal energy remaining in the bulk samples of metals and semiconductors following multi-pulse femtosecond laser ablation. In contrast to the previous belief that the thermal energy remaining in the ablated sample is negligible using femtosecond pulses, we show a significant amount of residual thermal energy deposited in various materials. In fact, with a sufficiently large number of pulses at high fluence, virtually all the incident laser energy can be retained in the sample. Several possible mechanisms are investigated for their role in residual heating, including laser-induced surface modification, exothermic chemical processes, and pressure effects. We show that the increase in sample absorptivity due to surface modification is the dominant factor for the enhanced residual heating at a sufficiently large number of applied pulses but this alone can not fully account for enhanced residual heating at a smaller number of pulses. [Preview Abstract] |
Tuesday, March 22, 2005 10:36AM - 10:48AM |
H28.00008: Calculation of optical absorption in Al accross the solid $\longrightarrow$ liquid transition Lorin X. Benedict, John E. Klepeis, Frederick H. Streitz We calculate the optical absorption spectrum of solid and liquid Al for temperatures between 0 K and 1800 K with an empirical pseudopotential technique. It is found that a prominent peak in the spectrum of the solid (at $\hbar\omega \sim$ 1.5 eV) disappears as the temperature is raised above T$_{\rm melt}=$ 938 K. This is in agreement with earlier measurements on solid and liquid Al, but is in disagreement with more recent measurements on the liquid, in which the peak was seen to remain at T= 1550 K. Our results suggest that {\it in situ} optical constants measurements may be used as a diagnostic for the shock melting of Al. [Preview Abstract] |
Tuesday, March 22, 2005 10:48AM - 11:00AM |
H28.00009: Homogeneous melting of superheated crystals Mattias Forsblom, G{\" o}ran Grimvall Homogeneous melting of crystals (i.e. not initiated at a surface) has been studied in many works but the detailed mechanism is still not well understood. We have carried out molecular-dynamics simulations for a realistic case (fcc Al) with the interaction of Ercolessi and Adams to thoroughly track the microscopic path of the solid-to-liquid transition. Due to periodic boundary conditions the surface-melting mechanism is suppressed and melting occurs in a superheated state at a temperature about $30~{\%}$ above the equilibrium melting point. We find that the thermal fluctuation initiating the melting process is an aggregate of point defects, with typically 6-7 interstitials and 3-4 vacancies, which acts as a nucleation site for the growth of the liquid phase. This picture differs from those previously proposed in that the configuration initiating melting involves much fewer particles. Other mechanisms are not necessarily false but we have identified the smallest defect configuration leading to melting. [Preview Abstract] |
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H28.00010: Glass formation by first-order transition in Al-Fe-Si system Leonid A. Bendersky, John W. Cahn There are two quite different views of metallic glasses. One, that a glass forms when an undercooled melt becomes kinetically frozen. This mechanism is quite universal and in principle occurs for all melts if they can be cooled rapidly enough. Usually such glasses tolerate wide compositional variations and occur at deep eutectics. The other view looks for efficient high-density low-energy packing of atoms in an aperiodic isotropic structure. These glasses, which we dubbed q-glasses, are expected to be less tolerant of composition variations and do not require deep eutectic. In our earlier publications we presented evidence of the existence of a q-glass in Al-Fe-Si. The glass was found to form from the melt as a primary phase by a nucleation and growth reaction before there is any crystallization was found to occur in. Here we present detailed study of formation of the Al-Fe-Si q-glass in a wide range of compositions. It was found that the glass behaves as a stoichiometric compound, with a concentration near 15 a/o Fe, 20 a/o Si. For other compositions formation of complex intermetallic compounds and an icosahedral phase were observed [Preview Abstract] |
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