Influence of annealing on structural relaxation, crystallization, and deformation behavior of a Zr 41.2 Ti 13.8 Cu 12.5
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yun-Joon Jun and Young Won Chang Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang 790-784, South Korea (Received 7 November 2006; accepted 15 March 2007)
The influence of annealing on the structural changes and the mechanical properties of Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit-1) bulk metallic glass was systematically studied by varying the annealing times at 703 K. The evolution of the structural state at a relatively high temperature within the supercooled liquid region was studied by thermal analysis, x-ray diffraction, high-resolution transmission electron microscopy, extended x-ray absorption fine structure, and dilatometric measurements. The deformation behavior and the mechanical properties were also examined by carrying out hardness and compression tests for the specimens annealed for various times.
I. INTRODUCTION
During the last decade, bulk metallic glasses (BMGs) with excellent glass forming ability have been found in many multicomponent alloy systems.1–5 In particular, Zrbased BMGs have attracted great attention due to their excellent mechanical properties including high strength, hardness, and elastic response at room temperature.5–8 In addition to the above-mentioned room temperature mechanical properties, these alloys are also known to exhibit enhanced ductility and superplastic-like extraordinary formability in the viscous state at elevated temperatures within the supercooled liquid region, promising application in the near-net-shape fabrication industries of structural parts through conventional mold casting and subsequent warm deformation.9–11 On the other hand, these BMGs are prone to crystallization, which leads to changes in the properties of the amorphous matrix when annealed for considerable time in the supercooled liquid region even below the crystallization temperature during high-temperature deformation or just upon annealing.12,13 Especially because the unique mechanical properties of monolithic BMGs change during crystallization
a)
Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http:// www.mrs.org/jmr_policy DOI: 10.1557/JMR.2007.0253 J. Mater. Res., Vol. 22, No. 7, Jul 2007
upon annealing in the supercooled liquid state, the crystallization characteristics of BMGs have been widely studied.14–19 In addition, monolithic BMGs show a tendency to structurally relax before crystallization because after rapid solidification, BMGs with liquid-like structure retain a non-equilibrium frozen-in structure.20,21 When a metallic glass is rapidly quenched, it retains a nonequilibrium structure that can be relaxed into more stable counterparts as a function of annealing time and temperature. This change of state is typically defined as structural relaxation. Proper annealing treatment is used as one of the basic processes to induce structural rela
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