Correlation of Microstructure with Mechanical Properties of Zr-Based Amorphous Matrix Composite Reinforced with Tungsten
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PLASTIC zones in monolithic amorphous alloys are hardly observed under tensile or compressive loading because the plastic deformation is concentrated on highly localized shear bands.[1–4] This is why monolithic amorphous alloys show stress–strain curves observed in typically brittle materials such as ceramics, and their plastic strain ranges a couple of percent even under compressive loading.[5,6] To improve their ductility, intensive studies on fabrication of amorphous matrix composites have been performed by dispersing ductile crystalline particles, phases, or fibers.[7–17] For example, a Zr-based amorphous alloy containing ductile dendrites CHANG-YOUNG SON, formerly Postdoctoral Research Associate, Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang 790-784, Korea, is now Senior Researcher, Next Generation Products Research Group, Technical Research Laboratories, POSCO, Pohang 790-300, Korea. GYEONG SU KIM, Research Assistant, and HYOUNG SEOP KIM, Professor, are with the Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, 790-784, Korea. SANG-BOK LEE and SANG-KWAN LEE, Senior Researchers, are with the Composite Materials Laboratory, Korea Institute of Materials Science, Chanwon 541-331, Korea. HOON HUH, Professor, is with the Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Daejeon 350-701. Korea. SUNGHAK LEE, Professor, is with the Center for Advanced Aerospace Materials and Department of Materials Science and Engineering, Pohang University of Science and Technology. Contact e-mail: shlee@postech. ac.kr Manuscript submitted September 26, 2011. Article published online July 4, 2012 4088—VOLUME 43A, NOVEMBER 2012
of crystalline b phases (structure, body-centered cubic [bcc]), i.e., an LM2 alloy (commercial brand name of the Liquidmetal Technologies, Lake Forest, CA; composition Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5 at. pct) shows the improved ductility by the formation of deformation bands at dendrites and multiple shear bands in the amorphous matrix.[18,19] Recently, a fabrication method of amorphous matrix composites reinforced with continuous metallic fibers, i.e., a liquid pressing process, was developed to improve simultaneously the strength and ductility of amorphous alloys.[20,21] Because this process uses a low pressure near to the theoretically required minimum loading pressure, the crystallization of the amorphous matrix can be prevented or minimized by rapid cooling of the amorphous melt. It also has the advantages of complete infiltration of the melt inside the fiber because of the application of low hydrostatic pressure and elimination of pores formed by contraction during solidification. By using this process, Lee et al.[22] fabricated an amorphous matrix composite reinforced with tungsten continuous fibers in a matrix of a monolithic Zr-based amorphous alloy, i.e., an LM1 alloy (commercial brand name of the Liquidmetal Technologies; composition: Zr41.2Ti13.8Cu12.5Ni10.0Be22
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