Investigation of the stability of glassy state in the Zr- and Hf-based glassy alloys correlated with their transformatio
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Mitsuhide Matsushita JEOL Ltd., Akishima, Tokyo 196-8558, Japan
Akihisa Inoue Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan (Received 25 May 2001; accepted 5 September 2001)
The transformation behavior from glassy state was investigated in Zr- and Hf-based glassy alloys. The primary phases are metastable face-centered-cubic (fcc) Zr2Ni and fcc Hf2Ni phases in the Zr65Al7.5Ni10Cu17.5 and Hf65Al7.5Ni10Cu17.5 glassy alloys, respectively. By substitution of 5 at.% Pd for Cu, the primary phase changes to an icosahedral quasicrystalline phase in both alloys. It is found that the addition of elements, which have a positive or weak chemical affinity with one of the constitutional elements in the Zr–Al–Ni–Cu and Hf–Al–Ni–Cu glassy alloys, is effective for the precipitation of the icosahedral phase. It is suggested that Pd plays a dominant role in an increase in the number of nucleation sites. Since an icosahedron is contained as a structure unit in the icosahedral, fcc Zr2Ni and fcc Hf2Ni phases, it is implied that these phases are correlated with the local icosahedral order. The high-resolution transmission electron microscopy images of the as-spun Zr65Al7.5Ni10Cu7.5Pd10 and Hf65Al7.5Ni10Cu12.5Pd5 alloys reveal a possibility of the existence of the icosahedral ordered regions. It is therefore, concluded that the icosahedral short- or medium-range order exists and it stabilizes the glassy state in the Zr- and Hf-based multicomponent alloys. I. INTRODUCTION
Since 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 in the aspects of the scientific interests 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 Moreover, it was reported that the Hf–Al–Ni–Cu glassy alloy has also a large supercooled liquid region,6,7 which explains the high GFA in the alloy. Recently, the precipitation of an icosahedral phase was reported in the Zr65Al7.5Ni10Cu17.5 and Hf65Al7.5Ni10Cu17.5 glassy alloys by addition of 5 or 10 at.% noble metal substituted for the Cu element.8–10 a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 16, No. 12, Dec 2001
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The icosahedral phase has a fine grain size with a diameter of less than approximately 50 nm, which exhibits a high nucleation rate. The authors have reported the icosahedral phase formation by addition of other elements, such as V, Nb, Ta, Ti, and Mo, which have positive or nearly zero mixing enthalpies against major constituent elements in the Zr–Al–Ni–Cu and Hf–Al–Ni–Cu alloys.11–13 It is interpreted that the icosahedral phase c
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