Thermal expansion of bulk amorphous Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 alloy
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Thermal expansion of bulk amorphous Zr41.2 Ti13.8 Cu12.5 Ni10 Be22.5 alloy Y. He, R. B. Schwarz, and D. G. Mandrusa) Center for Materials Science, MS K-765, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (Received 28 August 1995; accepted 12 February 1996)
The linear thermal expansion of the bulk amorphous Zr41.2 Ti13.8 Cu12.5 Ni10 Be22.5 (atomic percent) alloy has been measured from 80 K to 773 K. The data for T , Tg were fitted by a model based on the Gr¨uneisen relation and a Debye expression for the heat capacity. From the fit, we deduced the Gr¨uneisen parameter, g 1.25, and the Debye temperature, Q D 400 K. Annealing the amorphous alloy at 663 K, which is between the glass transition temperature Tg 623 K and the crystallization temperature Tx 693 K, causes viscous flow in the sample. This is due to the small viscosity in the undercooled liquid.
I. INTRODUCTION
Amorphous metallic alloys can be prepared by a variety of techniques. The most common, however, are those based on the undercooling of melts. To produce a glass, the melt must be cooled from the liquidus temperature, Tl , to the glass transition temperature, Tg , at a rate sufficiently fast to prevent crystallization. Once the undercooled liquid is cooled below Tg , the liquid is kinetically trapped in the glassy state. Because metallic bonding is largely nondirectional, atomic mobility in undercooled metallic liquid is, in general, very high, and thus the cooling rates required of glass synthesis are equally high. In fact, for most amorphous metallic alloys the required cooling rates are on the order of 106 –1010 K s21 . This high cooling rate imposes an intrinsic restriction on the morphology of these amorphous alloys since one sample dimension usually has to be less than 30 –50 mm. Although thin magnetic amorphous foils are being used in electrical transformers and motors,1 much larger dimensions are needed for most practical applications. There is a group of metallic alloys that can be trapped in the glassy state using much lower cooling rates. This group includes the alloys Pd40 Ni40 P20 ,2–4 Pd77.5 Cu6 Si16.5 , 5,6 Au55 Pb22.5 Sb22.5 , 7 La55 Al25 Ni10 Cu5 Co5 ,8 Mg65 Cu25 Y10 ,9,10 Zr65 Al7.5 Ni10 Cu17.5 ,11,12 and Zr41.2 Ti13.8 Cu12.5 Ni10 Be22.5 .13 These alloys have been synthesized into bulk amorphous form, with the minor dimension ranging from a few millimeters to over one centimeter. These alloys have the following in common: (a) more than two elements, and ( b) a high value of reduced glass temperature Trg TgyTl . As suggested by Turnbull,14 a high value of Trg means a low value of the thermodynamic a)
Present address: Oak Ridge National Laboratory, Bldg.-2000, MS 6056, P.O. Box 2008, Oak Ridge, Tennessee 37831-6056.
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http://journals.cambridge.org
J. Mater. Res., Vol. 11, No. 7, Jul 1996
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driving force for homogeneous crystal nucleation in the regime Tl 2 Tg . Bypassing crystallization in the undercooled regime also requires eliminating
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