Dynamic deformation and fracture behaviors of two Zr-based amorphous alloys
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Despite outstanding mechanical properties of amorphous alloys in strength, hardness, and resistance to wear and corrosion, they have limited applications due to poor ductility and fracture toughness. Many efforts have been currently made to improve ductility and fracture toughness of amorphous alloys by fabricating amorphous matrix composites containing ductile crystalline phases.[1–6] Johnson et al.[7] explained the plastic deformation and flow behaviors of Zr-based amorphous alloys using a self-consistent dynamic-free volume model, and Zhang et al.[8] investigated fracture mechanisms of Zr-based amorphous alloys, which varied with principal stress states under tensile and compressive loading conditions. However, deformation and fracture behaviors of amorphous alloys under dynamic loading are not actively studied because these studies are mostly related to phenomena occurring under quasi-static loading. Thus, it is required to obtain information on dynamic deformation and fracture behaviors of amorphous alloys so that it can be effectively applied to strategic fields
DONG-GEUN LEE, Senior Researcher, is with the Materials Processing Research Center, Korea Institute of Machinery and Materials, Changwon, 641-010 Korea. YANG GON KIM, Research Assistant, is with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, 790-784 Korea. SUNGHAK LEE and NACK J. KIM, Professors, Center for Advanced Aerospace Materials, Pohang University of Science and Technology, are jointly appointed with the Materials Science and Engineering Department, Pohang University of Science and Technology. Contact e-mail: [email protected] Manuscript submitted November 3, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS A
such as defense, aerospace, precision machinery, and automotive industries. Since resistance to deformation and fracture under dynamic loading can be lower than that under quasi-static loading,[9,10,11] studies on dynamic deformation and fracture behaviors are essential for evaluation of alloy designing, microstructural modification, and process control in high-speed manufacturing. In addition, it is hardly known how the abrupt shear deformation caused by shear bands under quasi-static loading differs from that under dynamic loading. In this study, quasi-static and dynamic compressive tests were conducted on Zr-based amorphous alloys, one of which contains ductile crystalline phases. Based on the test results, dynamic deformation and fracture mechanisms were elucidated. Using a universal testing machine and a dynamic Kolsky compression bar, compressive deformation and fracture behaviors were investigated at strain rates of 10–4 to 103 s–1. Fractured surfaces were observed using a scanning electron microscope (SEM) to analyze fracture mechanisms according to the fracture mode variation. The Zr-based amorphous alloys used in this study were ‘‘LM1’’ and ‘‘LM2’’ alloys (commercial brand names of the Liquidmetal Technologies, Lake Forest, CA), whose compositions were Zr41.2Ti13.8Cu12.5Ni10.0Be2
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