Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session J28: Focus Session: Metallic Glasses and Liquids II |
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Sponsoring Units: DMP Chair: Anup Gangopadhay, Washington University Room: LACC 506 |
Tuesday, March 22, 2005 11:15AM - 11:27AM |
J28.00001: Effect of shear-band formation and structural relaxation on mechanical properties of an Al-based metallic glass Wenhui Jiang, Michael Atzmon The effect of cold rolling on the mechanical behavior of amorphous Al$_{86.8}$Ni$_{3.7}$Y$_{9.5}$ has been investigated by nanoindentation. This alloy does not crystallize in response to plastic deformation at room temperature. While significant pile-ups are observed around indentations in the as-spun alloy, they are small in the rolled sample. It is also found that rolling reduces the hardness. Deformation of the as-spun alloy occurs by nucleation and propagation of shear bands, whereas the cold-rolled alloy deforms by propagation of pre- existing shear bands. Annealing leads to a recovery of the pile-ups, with the hardness increasing to above its value for the as-spun sample. Using high-resolution transmission electron microscopy, nanovoids are observed to be uniformly distributed in the shear bands formed due to rolling. Annealing does not appear to affect these nanovoids. This work was funded by the National Science Foundation, Grant DMR-0314214 [Preview Abstract] |
Tuesday, March 22, 2005 11:27AM - 11:39AM |
J28.00002: Shear Processes in Pd$_{40}$Ni$_{40}$P$_{20}$ Bulk Metallic Glasses D.J. Safarik, R.B. Schwarz Depending on the imposed deformation rate, plastic deformation in metallic glasses can be either Newtonian or non-Newtonian. To investigate the influence of deformation history on non-Newtonian plastic flow in bulk Pd$_{40}$Ni$_{40}$P$_{20}$ glass we deformed the same volume of the glass specimen along differently oriented glide planes. We found that the glass has a memory of its previous plastic deformation, but this memory is largely independent of the previous glide direction. Loss of the memory follows first-order kinetics with a time constant of 1260 s at 553 K. The transition from Newtonian to non-Newtonian flow is rather abrupt and occurs at a Deborah number, \textit{De = }$\dot {\gamma }\,\cdot \tau $ = 0.5, where $\dot {\gamma }$ is the plastic shear strain rate and $\tau $is the time constant for the exponential annihilation of the flow defects. This value of \textit{De} is consistent with the value of \textit{De} $\approx $ 1 observed at the onset of flow instabilities in liquids. The abruptness of the transition, together with the strong stress-sensitivity of the viscosity in the non-Newtonian regime, suggests that the plasticity agents in the Newtonian and non-Newtonian flow regimes are not the same. [Preview Abstract] |
Tuesday, March 22, 2005 11:39AM - 11:51AM |
J28.00003: A resonant ultrasound spectroscopy determination of the elastic constants of bulk metallic glasses Zhiying Zhang, Rapha\"el P. Hermann, Kathleen Affholter, Veerle Keppens, Mark L. Morrison, Guojiang Fan, Dongchun Qiao, Gongyao Wang, Raymond A. Buchanan, Hahn Choo, Peter K. Liaw, Joseph S. Poon, Yoshihiko Yokoyama It has been shown recently that the fragility of a glass-forming liquid is closely related to the elastic constants, and in particular to Poisson's ratio, of the corresponding glass phase.$^{1}$ Resonant ultrasound spectroscopy yields simultaneously the bulk and shear moduli of millimeter-sized samples, and thus provides a convenient and non-destructive way to determine Poisson's ratio of bulk metallic glasses. The elastic constants and Poisson's ratio of several bulk metallic glasses have been measured as a function of temperature between 5 and 400 K, and the obtained data will be compared to fragility measurements. [The support from NSF IGERT EEC-9984548 and DMR 0206625, and of DARPA SAM Program under ONR Grant N00014-01-1-0961 is acknowledged.] $^{1}$ Novikov V. N. and Sokolov A. P., \textit{Nature} \textbf{431}, 961-963 (2004) [Preview Abstract] |
Tuesday, March 22, 2005 11:51AM - 12:27PM |
J28.00004: NMR Observation of Dynamics in Metallic Supercooled Liquids and Glasses Invited Speaker: Dynamic crossover at temperature $T_{c} \quad > T_{g}$ in the supercooled liquid is an important issue for understanding the nature of glass transition. In a liquid of densely packed atoms, any given atom is temporarily trapped by the transient cage formed by neighboring atoms. Mode-coupling theory (MCT) predicts that such cage trapping of atoms undergoes a dynamic arrest below $T_{c}$ leading to a liquid to solid transition in the absence of hopping. Here we show that NMR could detect selectively different types of atomic motions based on their different spatial characteristics and timescales. The discussion will focus mostly on results obtained from the bulk metallic glass Pd$_{43}$Ni$_{10}$Cu$_{27}$P$_{20}$, one of the best glass formers with extremely high accessibility to the supercooled liquid region. We will show that the Knight shift of $^{31}$P is an NMR parameter sensitive to the Debye-Waller factor caused by local vibrations and cage rattling. Experiment shows that the mean-squared amplitude of such local motions depends linearly on $k_{B}T$ above a certain crossover temperature $T_{c}$ as well as below $T_{g}$ as expected by the equipartition theorem for harmonic vibrations. From $T_{c}$ down to $T_{g}$, the mean-squared amplitude decreases much more rapidly. Such crossover behavior is shown to be in good agreement with the prediction of the MCT with regard to motions of cage rattling. We will also show that NMR of quadrupolar nuclei $^{65}$Cu and $^{63}$Cu can probe the time correlation function of the local electric-field gradient (EFG) in the supercooled liquid. We measured the temperature dependence of the EFG correlation time which is closely related to atomic diffusion. Once again, the result is shown to be consistent with the prediction of the MCT. [Preview Abstract] |
Tuesday, March 22, 2005 12:27PM - 1:03PM |
J28.00005: Fast in-situ, high-resolution PDF analysis studies of glasses and nanocrystalline materials Invited Speaker: We are increasingly interested in complex materials for their unique functional properties. Complex materials often exhibit nanoscale local structures that are important in determining their properties. These come about from defects but often are intrinsic, coming from competing interactions in the materials. It is important to characterize these ``nanostructures'' but this is difficult because they are not, by their nature, long-range ordered and cannot be studied using traditional crystallographic methods. The atomic pair distribution function (PDF) analysis method has, for a long time, been used to study the structure of glasses and liquids. I will describe recent developments in both data collection and analysis that make this method a powerful quantitative probe of nanostructures. In particular, intense high energy x-rays from third generation synchrotron sources now make it possible to study materials in-situ under extreme conditions while studying their local atomic structure. The experiments are quick opening the way to time-resolve studies. [Preview Abstract] |
Tuesday, March 22, 2005 1:03PM - 1:39PM |
J28.00006: Role of Yttrium in Glass Formation of Bulk Metallic Glasses Invited Speaker: It was found experimentally that appropriate additions of yttrium in both Fe-based and Zr-based bulk metallic glasses can improve their glass-forming ability (GFA) dramatically$^{1,2}$. In this talk, focuses will be placed on understanding the beneficial effects of yttrium on glass formation in these alloy systems. Our studies indicated that the striking enhancement of the GFA in these systems is attributed to two factors: \begin{enumerate} \item Yttrium additions can successfully suppress the formation of competing crystalline phases, thus adjusting the composition to be closer to the eutectic and lowering the liquidus temperatures of the alloys (i.e., destabilizing the competing crystalline phases). \item Yttrium can also scavenge oxygen to form innocuous yttrium oxides from the undercooled liquid, thereby stabilizing the liquid phase. \end{enumerate} The current work demonstrates clearly that the GFA of bulk metallic glasses can be increased by either enhancing the liquid phase stability or suppressing the formation of competing crystalline phases, which further confirms and verifies our previous analysis$^{3}$. \newline \newline [1]. Z. P. Lu {\&} C. T. Liu, Phys. Rev. Lett., 92(2004)245503. \newline [2]. Z. P. Lu et al, Appl. Phys. Lett., 83(2003)2581. \newline [3]. Z. P. Lu {\&} C. T. Liu, Phys. Rev. Lett., 91(2003)115505. \newline \newline \newline This research was sponsored by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy under contract DE-AC05-00OR-22725 with UT-Battelle, LLC. . [Preview Abstract] |
Tuesday, March 22, 2005 1:39PM - 1:51PM |
J28.00007: Pair Distribution Function Study of Zr$_{55}$Cu$_{35}$Al$_{10}$ Bulk Metallic Glasses Cang Fan, T.W. Wilson, W. Dmowski, H. Choo, J.W. Richardson, E.R. Maxey, P.K. Liaw Despite strong interests in bulk metallic glasses for a variety of engineering applications, details of their structures still remain uncertain. During annealing bulk metallic glasses show heat release prior to the crystallization, which corresponds to the structural relaxation. To investigate the changes in local atomic structure (short-range to medium-range order) associated with the structural relaxation and partial crystallization, we carried out neutron-scattering measurements on the Zr$_{55}$Cu$_{35}$Al$_{10}$ bulk metallic Glasses subjected to three different heat treatment conditions: (1) as-quenched, (2) annealed at 703 K for 2.1 ks to induce structural relaxation, and (3) annealed at 703 K for 4.2 ks to partially crystallize. The neutron-scattering results were studies by pair distribution function analysis. In addition, high-resolution transmission electron microscopy and x-ray diffraction have been performed to investigate the as-cast structure and crystallization processes to complement the neutron-scattering structural studies. \textit{This work is supported by the NSF International Materials Institutes Program under DMR-0231320 with Dr. C. Huber as the Program Director.} [Preview Abstract] |
Tuesday, March 22, 2005 1:51PM - 2:03PM |
J28.00008: The Genesis Mission Metallic Glass Solar Wind Collector C. Hays, A. Jurewicz, J. Kulleck, M. Petkov, K. Kuhlman, K. McNamara, A. Grimberg, R. Wieler NASA's Genesis mission continuously exposed materials to the solar wind, and brought them back to Earth for analysis. Despite the hard impact landing of the sample return capsule in Sept./2004, some of the solar wind collectors were recovered in pristine condition; one was a metallic glass, with target composition Zr$_{58.5}$Nb$_{2.8}$Cu$_{15.6}$Ni$_{12.8}$Al$_{10.3}$. In this talk, we will describe the glassy alloy, the mission critical-properties, and expected science returns. Metallic glasses are well suited to measure solar wind components: 1) the disordered structure reduces fractionation during solar wind ion-implantation and loss of solar wind ions due to diffusion; and 2) an absence of grain boundaries eliminates high-diffusion-rate pathways. The glass will be analyzed for high-energy elements; e.g., He and Ne, with beyond solar wind energies. It is hoped that the glass will help elucidate the origin of solar energetic particles, a solar wind component with controversial origin. [Preview Abstract] |
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J28.00009: Structural and energetic properties of nickel clusters Michael Springborg, Valeri G. Grigoryan The four most stable structures of Ni$_N$ clusters with $N$ from 2 to 150 have been determined using a combination of the embedded-atom method in the version of Daw, Baskes and Foiles, the {\it variable metric/quasi-Newton} method, and our own {\it Aufbau/Abbau} method. A systematic study of energetics, structure, growth, and stability of also larger clusters has been carried through without more or less severe assumptions on the initial geometries in the structure optimization, on the symmetry, or on bond lengths. We present and apply different analytical tools in studying structural and energetic properties of such a large class of clusters. These include means for identifying the overall shape, the occurrence of atomic shells, the similarity of the clusters with, e.g., fragments of the {\it fcc} crystal or of a large icosahedral cluster, and a way of analysing whether the $N$-atom cluster can be considered constructed from the $(N-1)$-atom one by adding an extra atom. In addition, we compare in detail with results from chemical-probe experiment. Maybe the most central result is that first for clusters with $N$ above 80 general trends can be identified. [Preview Abstract] |
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