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Title: Structural Aspects of Metallic Glasses

Abstract

A recent structural model reconciles apparently conflicting features of randomness, short-range order, and medium-range order that coexist in metallic glasses. In this efficient cluster packing model, short-range order can be described by efficiently packed solute-centered clusters, producing more than a dozen established atomic clusters, including icosahedra. The observed preference for icosahedral short-range order in metallic glasses is consistent with the theme of efficient atomic packing and is further favored by solvent-centered clusters. Driven by solute-solute avoidance, medium-range order results from the organization in space of overlapping, percolating (via connected pathways), quasi-equivalent clusters. Cubic-like and icosahedral-like organization of these clusters are consistent with measured medium-range order. New techniques such as fluctuation electron microscopy now provide more detailed experimental studies of medium-range order for comparison with model predictions. Microscopic free volume in the efficient cluster packing model is able to represent experimental and computational results, showing free volume complexes ranging from subatomic to atomic-level sizes. Free volume connects static structural models to dynamic processes such as diffusion and deformation. New approaches dealing with 'free' and 'anti-free' microscopic volume and coordinated atomic motion show promise for modeling the complex dynamics of structural relaxations such as the glass transition. Future work unifying static andmore » dynamic structural views is suggested.« less

Authors:
 [1];  [2];  [2];  [2]
  1. AFOSR
  2. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
932147
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Research Bulletin; Journal Volume: 32
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ATOMIC CLUSTERS; AVOIDANCE; DEFORMATION; DIFFUSION; ELECTRON MICROSCOPY; FLUCTUATIONS; GLASS; METALLIC GLASSES; RANDOMNESS; SIMULATION; STRUCTURAL MODELS

Citation Formats

Miracle, Daniel, Egami, Takeshi, Flores, Katharine M, and Kelton, Kenneth. Structural Aspects of Metallic Glasses. United States: N. p., 2007. Web. doi:10.1557/mrs2007.124.
Miracle, Daniel, Egami, Takeshi, Flores, Katharine M, & Kelton, Kenneth. Structural Aspects of Metallic Glasses. United States. doi:10.1557/mrs2007.124.
Miracle, Daniel, Egami, Takeshi, Flores, Katharine M, and Kelton, Kenneth. Mon . "Structural Aspects of Metallic Glasses". United States. doi:10.1557/mrs2007.124.
@article{osti_932147,
title = {Structural Aspects of Metallic Glasses},
author = {Miracle, Daniel and Egami, Takeshi and Flores, Katharine M and Kelton, Kenneth},
abstractNote = {A recent structural model reconciles apparently conflicting features of randomness, short-range order, and medium-range order that coexist in metallic glasses. In this efficient cluster packing model, short-range order can be described by efficiently packed solute-centered clusters, producing more than a dozen established atomic clusters, including icosahedra. The observed preference for icosahedral short-range order in metallic glasses is consistent with the theme of efficient atomic packing and is further favored by solvent-centered clusters. Driven by solute-solute avoidance, medium-range order results from the organization in space of overlapping, percolating (via connected pathways), quasi-equivalent clusters. Cubic-like and icosahedral-like organization of these clusters are consistent with measured medium-range order. New techniques such as fluctuation electron microscopy now provide more detailed experimental studies of medium-range order for comparison with model predictions. Microscopic free volume in the efficient cluster packing model is able to represent experimental and computational results, showing free volume complexes ranging from subatomic to atomic-level sizes. Free volume connects static structural models to dynamic processes such as diffusion and deformation. New approaches dealing with 'free' and 'anti-free' microscopic volume and coordinated atomic motion show promise for modeling the complex dynamics of structural relaxations such as the glass transition. Future work unifying static and dynamic structural views is suggested.},
doi = {10.1557/mrs2007.124},
journal = {Materials Research Bulletin},
number = ,
volume = 32,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • We have examined the dependence of microhardness in As{sub 2}S{sub 3}-As{sub 2}Se{sub 3} alloys on composition, temperature, and loading time, and have compared the results with data for glasses. We examined (As{sub 2}S{sub 3}){sub 1-x}(As{sub 2}Se{sub 3}){sub x}, where x was 0: 0.3; 0.4; 0.5; 0.6; 0.7; 0.8; 0.9; 1. Alloys with those compositions were prepared by ordinary melting of the components in evacuated silica tubes at 950 K. The microhardness was measured with a PMT-3 tester at a constant load of 0.1 kg. The maximum microhardness occurred for x = 0.4, and the form of the dependence is characteristicmore » of many amorphous and crystalline materials that form homogeneous alloys with composition variation. For all the compositions, the microhardness decreased exponentially as the time increased. We measured the temperature dependence of the microhardness over the range 300-450 K. Above 450 K, the surfaces oxidized and it was not possible to observe the boundaries of the pyramid indents. The methods developed for glasses are thus applicable to these amorphous alloys.« less
  • High-pressure x-ray diffraction studies have been carried out on the two group IV transition metals-based bulk metallic glasses (BMGs) Zr{sub 57}Cu{sub 15.4}Ni{sub 12.6}Al{sub 10}Nb{sub 5} and Ti{sub 42}Zr{sub 24}Cu{sub 15.5}Ni{sub 14.5}Be{sub 4} to a pressure of 30 GPa at ambient temperature in a diamond anvil cell. Image plate x-ray diffraction studies under high pressure were carried out at a synchrotron source and the two BMG diffraction bands can be followed to the highest pressure using an internal copper pressure standard. The amorphous phase is observed to be stable to the highest static pressure of 30 GPa suggesting that the phasemore » change observed in dynamical pressure experiments is related to an increase in temperature. The measured bulk modulus (B{sub 0}) and its pressure derivative (B') are 118 GPa and 3.11 for Zr-based BMG and 116 GPa and 2.84 for Ti-based BMG. The measured bulk modulus for BMG's by x-ray diffraction technique is consistent with the ultrasonic measurements. The decompression data reveal an increase in density by 3%-4% at ambient condition after pressure cycling to 30 GPa indicating reduction in excess free volume.« less
  • We observed structural anisotropy in metallic glasses samples deformed by homogenous mechanical creep and by inhomogeneous compression using high energy X-ray diffraction. Pair distribution function analysis indicates bond anisotropy in the first atomic shell. This suggests that mechanical deformation involves rearrangements in a cluster of atoms by a bond reformation.
  • Metallic glasses have been studied vigorously since the first report on amorphous gold-silicon alloy back in 1960.[1] Initially soft magnetic properties were the most promising features for industrial applications. The recent development of bulk metallic glasses (BMGs)[2 5] initiated interests in engineering applications such as structural or biomedical materials because of attractive properties such as high strength,[6] high elasticity,[7,8] and good corrosion resistance,[9,10] among others. In addition, high temperature processing of BMGs allows for near-net-shape formability,[11 13] which could simplify and possibly reduce the cost of the final product. The glasses retain the disordered atomic structure of a liquid, andmore » ideally are isotropic solids. Frequently because of processing conditions, such as directional heat flow, some structural anisotropy is produced during quenching, and has been observed by structural investigations. Usually, annealing at high temperatures results in an isotropic structure. Also, formation of uniaxial magnetic anisotropy[14] had been observed in studies of creep deformed ferromagnetic metallic glasses. Samples with a near-zero magnetostriction coefficient had been studied to establish the origin of the magnetic anisotropy. It was concluded that anisotropy resulted from the atomic level anisotropy[15] and not the heterogeneous internal stress distribution. Indeed X-ray diffraction study of the creep deformed metallic glass showed bond anisotropy.[ 16,17] Such structural studies had been cumbersome and lengthy because they required measurement of many orientations with high statistics. Recently we have shown that use of an area detector and high energy X-rays at a synchrotron source can speed up data collection without compromising statistics.[18] In this contribution, we present data showing structural anisotropy in glassy samples after homogenous (creep) and inhomogeneous (compression) mechanical deformation. The observation of the structural anisotropy after mechanical deformation can provide insight into the atomistic mechanism of the deformation process in metallic glasses.« less