Role of free volume in strain softening of as-cast and annealed bulk metallic glass

Byung Gil Yoo, Kyoung Won Park, Jae Chul Lee, U. Ramamurty, Jae Il Jang

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55 Citations (Scopus)

Abstract

Plasticity in amorphous alloys is associated with strain softening, induced by the creation of additional free volume during deformation. In this paper, the role of free volume, which was a priori in the material, on work softening was investigated. For this, an as-cast Zr-based bulk metallic glass (BMG) was systematically annealed below its glass transition temperature, so as to reduce the free volume content. The bonded-interface indentation technique is used to generate extensively deformed and well defined plastic zones. Nanoindentation was utilized to estimate the hardness of the deformed as well as undeformed regions. The results show that the structural relaxation annealing enhances the hardness and that both the subsurface shear band number density and the plastic zone size decrease with annealing time. The serrations in the nanoindentation load-displacement curves become smoother with structural relaxation. Regardless of the annealing condition, the nanohardness of the deformed regions is ∼12-15% lower, implying that the prior free volume only changes the yield stress (or hardness) but not the relative flow stress (or the extent of strain softening). Statistical distributions of the nanohardness obtained from deformed and undeformed regions have no overlap, suggesting that shear band number density has no influence on the plastic characteristics of the deformed region.

Original languageEnglish
Pages (from-to)1405-1416
Number of pages12
JournalJournal of Materials Research
Volume24
Issue number4
DOIs
Publication statusPublished - 2009 Apr

Bibliographical note

Funding Information:
This research was supported by the Korea Research Foundation (KRF) grant funded by the Korean Government, MEST (Grant No. KRF-2006-331-D00273), and partially by the Korea Science and Engineering Foundation (KOSEF) grant funded by MEST (Grant No. R01-2008-000-20778-0). One of the authors, U.R., acknowledges the financial support received for this work from the Department of Science and Technology, Government of India through a Swarna Jayanthi Fellowship. The authors thank Dr. H. Bei (at Oak Ridge National Laboratory) for providing the samples, and Mr. B-W. Choi (at Hanyang University) for his assistance in calculating the discrete plasticity ratio.

ASJC Scopus subject areas

  • General Materials Science
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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