Thermodynamics of The Pd 43 Ni 10 Cu 27 P 20 Bulk Metallic Glass Forming Alloy
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Thermodynamics of The Pd43Ni10Cu27P20 Bulk Metallic Glass Forming Alloy Masahiro Kuno, Ludi A. Shadowspeaker, Jan Schroers1, and Ralf Busch Department of Mechanical Engineering, Oregon State University, Corvallis Oregon 97331 1 Keck Laboratory of Engineering Materials, California institute of technology, Pasadena, CA 91125 ABSTRACT The thermodynamics of the bulk metallic glass forming Pd43Ni10Cu27P20 alloy were investigated with differential scanning calorimetry (DSC). The specific heat capacity of the undercooled liquid with respect to the crystalline mixture was measured in the DSC simultaneously with the enthalpy of crystallization over the entire supercooled liquid region. The enthalpy, entropy, and Gibbs free energy change between the liquid and the crystalline mixture was determined from the specific heat capacity data. The calculated enthalpy function closely matched the enthalpies of crystallization that were measured in the DSC, which verifies the validity of the thermodynamic model used. A small Gibbs free energy difference between undercooled liquid and crystalline mixture was found for decreasing temperature in Pd43Ni10Cu27P20 when compared to other glass forming alloys. This reflects a small driving force for crystallization when undercooling this alloy and is the main contributing factor for its high glass forming ability. INTRODUCTION Multicomponent glass forming alloy families such as La-Al-Ni [1], Mg-Cu-Y [2], Zr-TiCu-Ni-Be [3], and Zr-Ni-Al-Cu [4], exhibit very good glass forming ability. These bulk metallic glasses (BMG) show high thermal stability with respect to crystallization, which allows for detailed studies of their thermodynamic properties in the undercooled liquid state. An essential thermodynamic property is the specific heat capacity, cp, of the undercooled liquid because, when referenced to the cp of the crystal, the thermodynamic functions of enthalpy, entropy, and Gibbs free energy can be derived by well-defined integration functions [5]. This study focuses on the thermodynamics of the Pd43Ni10Cu27P20 BMG [6]. This alloy has a lower critical cooling rate, when processed in B2O3 [7], than the other Pd-Ni-P based alloys that have been studied so far [8]. The goal of this investigation is to measure the specific heat capacity and the enthalpy of crystallization of undercooled Pd43Ni10Cu27P20 as a function of temperature and compare the experimental enthalpy change with the enthalpy change that can be calculated from the specific heat capacity difference between undercooled liquid and crystalline mixture. EXPERIMENTAL METHODS Pd43Ni10Cu27P20 ingots were prepared from a mixture of the elements with a purity ranging from 99.0% to 99.999% by induction melting in quartz tubes. To obtain glass, the melt was held at 1200 K for 1200 s and then quenched in water. The samples were fluxed with B2O3 during this procedure to prevent crystallization. Glassy Pd43Ni10Cu27P20 samples up to 70 mg and an additional 3 to 5 mg of flux were introduced into graphite crucibles and analyzed in a Perkin
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