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Title: Improving the mechanical properties of Zr-based bulk metallic glass by controlling the activation energy for β-relaxation through plastic deformation

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{sub 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 tensilemore » 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
Authors:
; ;  [1] ;  [2]
  1. Department of Mechanical Engineering, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku, Toyohashi, Aichi 441-8580 (Japan)
  2. Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan)
Publication Date:
OSTI Identifier:
22350794
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 105; Journal Issue: 13; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ACTIVATION ENERGY; ALUMINIUM COMPOUNDS; COPPER COMPOUNDS; CRYSTAL DEFECTS; ELONGATION; ENTHALPY; GLASS; METALLIC GLASSES; PLASTICITY; PLASTICS; POTENTIAL ENERGY; RELAXATION; STRAINS; TRANSFORMATIONS; TRANSITION TEMPERATURE; YIELD STRENGTH; ZIRCONIUM COMPOUNDS