A Study of Amorphous Erbium-Based Alloys Formed by Near-Isothermal Cold-Rolling of Elemental Composites
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A STUDY OF AMORPHOUS ERBIUM-BASED ALLOYS FORMED BY NEAR-ISOTHERMAL COLD-ROLLING OF ELEMENTAL COMPOSITES
KARL M. UNRUH**, CONSTANTIN POLITIS*** AND WILLIAM MICHAEL ATZMON*, L. JOHNSON, W. M. Keck Laboratory of Engineering Materials, California Institute of Technology, Pasadena, California 91125. * present address: Division of Applied Sciences, Harvard University, Cambridge, Massachusetts 02138. ** present address: Department of Physics, University of Delaware, Newark, Delaware 19711. * Kernforschungszentrum Karlsruhe, Institut fur Nukleare Festkorperphysik, Postfach 3640, D-7500 Karlsruhe, Fed. Rep. of Germany.
ABSTRACT We report the formation of single-phase amorphous Cu-Er and Ni-Er alloys in bulk form by cold-rolling of composites prepared from elemental foils. As for previously reported cases of metallic glass formation by solid-state reaction, the driving force for the reaction is the negative enthalpy of mixing of the constituent elements. It occurs during deformation close to room temperature. Amorphous CuT 2 Er 2 , was also produced by high-energy ball-milling of the elemental powders as well as by sputtering and liquid quenching. The alloys obtained were characterized by means of differential scanning calorimetry and x-ray diffraction. The crystallization behavior observed and the radial distribution functions obtained showed good agreement between the alloys prepared by different methods.
INTRODUCTION In
recent
years
it
has
been
shown
that
a
solid-state
reaction
of
elemental polycrystalline metals can result in the formation of an amorphous phase [1]. Thin layers of polycrystalline Au and La reacted at 80 0C to form amorphous Au-La alloys. The reaction was explained as driven by the large and negative enthalpy of mixing of the constituent elements. In a related experiment, Koch et al. [2] demonstrated that high-energy ball-milling of elemental Ni and Nb powders resulted in the formation of amorphous alloy powder. Further studies of amorphous alloys prepared by ball-milling and their comparison to rapidly quenched alloys have been reported [3-53. We have recently reported the extension of the thin film diffusion experiment to three dimensions [6]. Amorphous Cu-Zr and Ni-Zr alloys were produced by solid-state reaction in elemental composites. The composites were prepared by mixing elemental foils or powders and cold-rolling them. Schultz [7] reported experiments based on the same principle. In this study, Ni-Er and Cu-Er were selected for the following reason: 1) rare-earth alloys are of interest for magnetic applications, 2) amorphous rare-earth based alloys have been studied by many authors. Erbium was chosen as the rare-earth element because of its relatively low oxidation rate in air and its high ductility. Based on reported calorimetric measurements of the enthalpy of dissolution of Er in liquid Cu [8] and the regular solution approximation, we estimate the enthalpy of formation of liquid CuEr from the liquid elements to be approximately 19 kJ/mol. We are not aware of calorimetric data fo
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