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Title: Thermal activation in Au-based bulk metallic glass characterized by high-temperature nanoindentation

Abstract

High-temperature nanoindentation experiments have been conducted on a Au{sub 49}Ag{sub 5.5}Pd{sub 2.3}Cu{sub 26.9}Si{sub 16.3} bulk metallic glass from 30 to 140 deg. C, utilizing loading rates ranging from 0.1 to 100 mN/s. Generally, the hardness decreased with increasing temperature. An inhomogeneous-to-homogeneous flow transition was clearly observed when the test temperature approached the glass transition temperature. Analyses of the pop-in pattern and hardness variation showed that the inhomogeneous-to-homogeneous transition temperature was loading-rate dependent. Using a free-volume model, the authors deduced the size of the basic flow units and the activation energy for the homogeneous flow. In addition, the strain rate dependency of the transition temperature was predicted.

Authors:
; ;  [1];  [2];  [2]
  1. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20971809
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 90; Journal Issue: 6; Other Information: DOI: 10.1063/1.2459383; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ACTIVATION ENERGY; COPPER ALLOYS; GOLD ALLOYS; HARDNESS; LOADING RATE; METALLIC GLASSES; PALLADIUM ALLOYS; SILICON ALLOYS; SILVER ALLOYS; STRAIN RATE; TEMPERATURE RANGE 0273-0400 K; TRANSITION TEMPERATURE

Citation Formats

Yang Bing, Wadsworth, Jeffrey, Nieh, Tai-Gang, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6115, and Department of Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee 37996. Thermal activation in Au-based bulk metallic glass characterized by high-temperature nanoindentation. United States: N. p., 2007. Web. doi:10.1063/1.2459383.
Yang Bing, Wadsworth, Jeffrey, Nieh, Tai-Gang, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6115, & Department of Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee 37996. Thermal activation in Au-based bulk metallic glass characterized by high-temperature nanoindentation. United States. doi:10.1063/1.2459383.
Yang Bing, Wadsworth, Jeffrey, Nieh, Tai-Gang, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6115, and Department of Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee 37996. Mon . "Thermal activation in Au-based bulk metallic glass characterized by high-temperature nanoindentation". United States. doi:10.1063/1.2459383.
@article{osti_20971809,
title = {Thermal activation in Au-based bulk metallic glass characterized by high-temperature nanoindentation},
author = {Yang Bing and Wadsworth, Jeffrey and Nieh, Tai-Gang and Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6115 and Department of Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee 37996},
abstractNote = {High-temperature nanoindentation experiments have been conducted on a Au{sub 49}Ag{sub 5.5}Pd{sub 2.3}Cu{sub 26.9}Si{sub 16.3} bulk metallic glass from 30 to 140 deg. C, utilizing loading rates ranging from 0.1 to 100 mN/s. Generally, the hardness decreased with increasing temperature. An inhomogeneous-to-homogeneous flow transition was clearly observed when the test temperature approached the glass transition temperature. Analyses of the pop-in pattern and hardness variation showed that the inhomogeneous-to-homogeneous transition temperature was loading-rate dependent. Using a free-volume model, the authors deduced the size of the basic flow units and the activation energy for the homogeneous flow. In addition, the strain rate dependency of the transition temperature was predicted.},
doi = {10.1063/1.2459383},
journal = {Applied Physics Letters},
number = 6,
volume = 90,
place = {United States},
year = {Mon Feb 05 00:00:00 EST 2007},
month = {Mon Feb 05 00:00:00 EST 2007}
}
  • High-temperature nanoindentation experiments have been conducted on a Au49Ag5.5Pd2.3Cu26.9Si16.3 bulk metallic glass from 30 to 140 C, utilizing loading rates ranging from 0.1 to 100 mN/s. Generally, the hardness decreased with increasing temperature. An inhomogeneous-to-homogeneous flow transition was clearly observed when the test temperature approaches the glass transition temperature. Analyses of the pop-in pattern and hardness variation showed that the inhomogeneous-to-homogeneous transition temperature was loading-rate dependent. Using a free-volume model, we successfully deduced the size of the basic flow units and the activation energy for the homogeneous flow. In addition, the strain-rate dependency of the transition temperature was predicted.
  • Instrumented nanoindentation tests were used to investigate the mechanical properties of Zr{sub 52.5}Cu{sub 17.9}Ni{sub 14.6}Al{sub 10}Ti{sub 5} bulk metallic glass. The corresponding loading strain rates were ranged from 0.002 s{sup −1}, 0.02 s{sup −1} to 0.2 s{sup −1}. Plastic flow of this material exhibited remarkable serrations at low strain rates and increasingly became weakening until disappearance with increasing indentation strain rate, implying strong rate sensitivity. A significant pile-up around the indents was observed through atomic force microscopy, which suggested a highly localized plastic deformation. Mechanism governing the deformation was tentatively discussed in terms of the increasing process of free volume with a negligiblemore » temperature rise under low strain rate, which well explained the declining trend of elastic modulus and hardness with an increase of indentation depth.« less
  • Mechanical properties and glass transition temperatures (T{sub g}) of Fe-Cr-Mo-P-C-B bulk metallic glasses containing up to 27 at. % metalloids have been studied. The shear modulus (G) is found to decrease with increasing metalloid content and a maximum plastic strain of {approx}3% is obtained, despite the increase in the number of strong metal-metalloid bonds. Also, T{sub g} increases with the decrease in G, in contrast to usual behavior. By employing first-principles calculations, the results are discussed in light of atomic bonding and connectivity in the amorphous network. The findings are relevant to understanding ductility and glass transition of metallic glasses.
  • Structural relaxation of glasses below their glass transition is a well-studied phenomenon that still poses several open issues. With the advent of bulk metallic glasses with exceptionally low glass transition temperatures, new options are available that are based on the experimental assessment of the time dependence of several different thermodynamic quantities by direct measurements with high accuracy. In this contribution the first direct measurement of the isothermal relaxation of the volume and the enthalpy of an Au-based bulk metallic glassformer are reported and discussed with respect of the characteristics describing the underlying processes.
  • The mechanism of plastic deformation in bulk metallic glasses (BMGs) is widely believed to be based on a shear transformation zone (STZ). This model assumes that a shear-induced atomic rearrangement occurs at local clusters that are a few to hundreds of atoms in size. It was recently postulated that the potential energy barrier for STZ activation, W{sub STZ}, calculated using the cooperative shear model, is equivalent to the activation energy for β-relaxation, E{sub β}. This result suggested that the fundamental process for STZ activation is the mechanically activated β-relaxation. Since the E{sub β} value and the glass transition temperature T{submore » g} of BMGs have a linear relation, that is, because E{sub β} ≈ 26RT{sub g}, the composition of the BMG determines the ease with which the STZ can be activated. Enthalpy relaxation experiments revealed that the BMG Zr{sub 50}Cu{sub 40}Al{sub 10} when deformed by high-pressure torsion (HPT) has a lower E{sub β} of 101 kJ/mol. The HPT-processed samples accordingly exhibited tensile plastic elongation (0.34%) and marked decreases in their yield strength (330 MPa). These results suggest that mechanically induced structural defects (i.e., the free volume and the anti-free volume) effectively act to reduce W{sub STZ} and increase the number of STZs activated during tensile testing to accommodate the plastic strain without requiring a change in the composition of the BMG. Thus, this study shows quantitatively that mechanically induced structural defects can overcome the compositional limitations of E{sub β} (or W{sub STZ}) and result in improvements in the mechanical properties of the BMG.« less