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

Published online by Cambridge University Press:  31 January 2011

Byung-Gil Yoo ,
Kyoung-Won Park ,
Jae-Chul Lee ,
U. Ramamurty  and
Jae-il Jang
Byung-Gil Yoo
Affiliation:
Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, Korea
Kyoung-Won Park
Affiliation:
Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, Korea
Jae-Chul Lee
Affiliation:
Department of Materials Science and Engineering, Korea University, Seoul 136-701, Korea
U. Ramamurty
Affiliation:
Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India
Jae-il Jang*
Affiliation:
Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, Korea
*
a) Address all correspondence to this author. e-mail: jijang@hanyang.ac.kr
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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.

Keywords

AmorphousHardnessNanoindentation
Type
Articles
Information
Journal of Materials Research , Volume 24 , Issue 4 , April 2009 , pp. 1405 - 1416
Copyright
Copyright © Materials Research Society 2009

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