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

Yoo, Byung-Gil and Park, Kyoung-Won and Lee, Jae-Chul and Ramamurty, U and Jang, Jae-il (2009) Role of free volume in strain softening of as-cast and annealed bulk metallic glass. In: Journal of material research, 24 (4). pp. 1405-1416.

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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 similar to 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.

Item Type: Journal Article
Publication: Journal of material research
Publisher: Materials research society
Additional Information: Copyright for this article belongs to Materials research society.
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited: 23 Dec 2009 09:44
Last Modified: 23 Dec 2009 09:44
URI: http://eprints.iisc.ac.in/id/eprint/21471

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