Redistribution behavior of constitutional elements at an initial crystallization stage in the Zr 65 Al 7.5 Ni 10 Cu 17.5
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A. Inoue Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan (Received 9 September 2000; accepted 11 October 2000)
We investigated the transformation behavior from glassy to Zr2Ni phase in the Zr65Al7.5Ni10Cu17.5 glassy alloy with a low oxygen content below 400 ppm mass%. The mostly single face centered cubic Zr2Ni phase precipitated as a primary phase at the initial crystallization stage. The Zr2Ni particles had a cubical morphology in the diameter range of 300 to 500 nm and were in an isolated state for the sample annealed at the temperature near crystallization temperature. A significant redistribution leading to the enrichment of Zr and Ni into the Zr2Ni phase is confirmed. Moreover, it is recognized that Cu and Al are rejected from the Zr2Ni phase. The compositional differences of Zr, Al, Ni, and Cu between the Zr2Ni and remaining glassy phases are in the range of 1.5 to 5 at.%. It is strongly suggested that such a significant redistribution of the constitutional elements restrains the nucleation and growth of crystalline phases. It is one of the important factors for the stabilization of the glassy state in Zr–Al–Ni–Cu alloy.
Recently, a number of bulk glassy alloys with extremely high glass-forming ability (GFA) were found in Zr-based multicomponent alloy systems.1–3 They have attracted much attention because of scientific interest in a high stability of glassy state as well as industrial applications.4 Among Zr–Al–TM (TM ⳱ transition metals) alloy systems, the Zr65Al7.5Ni10Cu17.5 glassy alloy has an extremely high GFA as is evidenced by the largest value of the supercooled liquid region, which is defined as the temperature interval between glass-transition temperature and crystallization temperature.5 Ko¨ster et al. have reported that an icosahedral phase is formed as a primary crystallization phase in the Zr65Al7.5Ni10Cu17.5 glassy alloy with a high amount of oxygen content as an impurity.6 It has subsequently been noticed that the transformation behavior strongly depends on the oxygen and/ or hydrogen content in the Zr-based glassy alloys.7,8 Recently, it has been clarified that the face-centeredcubic (fcc) Zr2Ni phase with a large unit cell is formed in the Zr65Al7.5Ni10Cu17.5 glassy alloy with a low oxygen impurity.9,10 One of the authors has suggested that a long-range or a large-magnitude redistribution of the constitutional elements is necessary during the transfora)
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J. Mater. Res., Vol. 16, No. 1, Jan 2001 Downloaded: 14 Mar 2015
mation from glassy to crystalline phase, which is one of the important factors for stabilization of glassy state.11 However, little is known about direct evidence of the redistribution behavior especially at the initial crystallization stage, where the transformation behavior is strongly correlated with a glassy structure with high GFA. In this paper, we present a redistribution behavior of constitutional elements at the initial crystall
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