Glass to Icosahedral Phase Transformation in Zr-based Glassy Metals
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Glass to Icosahedral Phase Transformation in Zr-based Glassy Metals Osami Haruyama, Tomoaki Miyazawa, Junji Saida1 and Akihisa Inoue2 Department of Physics, Science University of Tokyo, Noda 278-8510, JAPAN 1 Japan Science and Technology Co, Inoue Superliquid Glass Project, Sendai 982-0807, JAPAN 2 Institute for Material Research, Tohoku University, Sendai 980-8577, JAPAN ABSTRACT Electrical properties of icosahedral phases (I-phase) that precipitated in Zr65Al7.5Cu7.5Ni10M10 (M=Ag, Pd), Zr65Al7.5Cu12.5Ni10M5 (M=Ag, Pd), Zr65Pd25Ni10 and Zr70Pd20Ni10 metallic glasses have been investigated. In-situ resistivity change with increasing temperature was measured at a heating rate of 0.67 K/s from room temperature. I-phase transformation was occurred in the supercooled liquid phase for Zr-Al-Cu-Ni-M glasses, followed by the crystallization to stable Zr2Ni- and Zr2Cu-type crystals. Ternary glasses exhibited the I-phase crystallization from the glass solid phase and subsequently the transformation of I-phase to crystal phases like Zr2Ni and Zr2Pd. The resistivity of I-phase decreased together with advancing I-phase precipitation, about 2 % compared to the resistivity of the supercooled liquid phase, for typical Zr65Al7.5Cu7.5Ni10Ag10 glass. On the other hand, Zr70Pd20Ni10 glass showed the resistivity increment of about 5 % just after completing I-phase crystallization. Low temperature conductivity of Zr65Al7.5Cu7.5Ni10Ag10 and Zr70Pd20Ni10 glasses and I-phases may be explained by the weak localization model of conduction electron in the range from about 20 K to room temperature.
INTRODUCTION Since the first discovery by Köster et al. [1], a lot of metallic glasses which exhibit the transformation to I-phase, such as Zr65Al7.5Cu7.5Ni10M10 (M=Pd, Ag),[2-4], Zr65Al7.5Cu12.5-Ni10M5 (M=Pd, Ag)[5], Zr70M20Ni10 (M=Pd, Ag, Pt)[6] and Zr70Pd30[7], have been prepared. These glasses show distinct two-step crystallization which first step corresponds to I-phase precipitation and second one to the transformation to stable crystal phases from I-phase. The I-phase crystallization of Zr-based glass is characterized by the nucleation and the growth process with the numerous density of nucleus. Therefore, the mean size of icosahedral grain is a typical order of 20 nm[4] and is below only 10 nm for Zr70Cu10M20 (M=Fe, Co) glasses [8], where X-ray diffraction is impossible to detect the structural change. The kinetics of I-phase crystallization has been investigated with Johnson-Mehl-Avrami analysis. The Zr65Al7.5Cu7.5Ni10Ag10 glass exhibited the Avrami exponent n§4, meaning strictly to the polymorphous crystallization [2]. On the other hand, Zr65Al7.5Cu7.5Ni10Pd10 glass [4] showed that I-phase crystallization was controlled by the volume diffusion with an increasing nucleation rate, which was concluded from the Avrami exponent n§3 and Y3.39.1
transmission electron microscopy (TEM). The electron probe microanalysis (EPMA) elucidated that the composition of alloy was slightly different between amorphous and icosahedral phases for Zr65Al7.5Cu7
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