Thermodynamics and kinetics of the undercooled liquid and the glass transition of the Zr41.2Ti13.8Cu,2.5Ni10.0Be22.5 alloy Differential scanning calorimetry (DSC) was used to determine the thermodynamic functions of the undercooled liquid and the amorphous phase with respect to the crystalline state of the ~41.2Ti13.8CU125Nilo.OBe22.5 bulk mltallic glass forming alloy. The specific heat capacities of this alloy. in the undercooled liquid, the amorphous state and the crystal were determined. The differences in enthalpy, AH, entropy, AS, and Gibbs free energy, AG, between crystal and the undercooled liquid were calculated using the measured specific heat capacity data as well as the heat of fusion. The results indicate that the Gibbs free energy difference between metastable undercooled liquid and crystalline solid, AG, stays small compared to conventional metallic glass forming alloys even for large undercoolings. Furthermore, the Kauzmann temperature, TK, where the entropy of the undercooled liquid equals to that of the crystal, was determined to be 560 K. The Kauzmann temperature is compared with the experimentally observed rate-dependent glass transition temperature, TR. Both onset and end temperatures of the glass transition depend linearly on the logarithm of the heating rate based on the DSC experiments. Those characteristic temperatures for the kinetically observed glass transition become equal close to the Kauzmann temperature in this alloy, which suggests an underlying thermodynamic glass transition as a lower bound for the kinetically observed freezing process. 0 1995 American Institute of Physics.

Various sample sizes of Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 with masses up to 80 mg were undercooled below T g ͑the glass transition temperature͒ while electrostatically levitated. The final solidification product of the sample was determined by x-ray diffraction to have an amorphous phase. Differential scanning calorimetry was used to confirm the absence of crystallinity in the processes sample. The amorphous phase could be formed only after heating the samples above the melting temperature for extended periods of time in order to break down and dissolve oxides or other contaminants which would otherwise initiate heterogeneous nucleation of crystals. Noncontact pyrometry was used to monitor the sample temperature throughout processing. The critical cooling rate required to avoid crystallization during solidification of the Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 alloy fell between 0.9 and 1.2 K/s. © 1994 American Institute of Physics.Extensive effort has been devoted to the preparation and characterization of metallic glass alloys. 1 Conventional rapid quenching techniques such as melting spinning, splat quenching, and liquid atomization have been employed to achieve the high undercooling required for glass formation by bypassing heterogeneous nucleation via rapid cooling at 10 3 -10 6 K/s. Modest cooling rates of 10 3 K/s or less have been applied to attain deep undercoolings in many binary and ternary alloys such as Pd-Si, 2 Pd-Cu-Si, 3 Au-Pb-Sb, 4 and Pd-Ni-P. 3,5 Very slow cooling rates ͑0.3 K/s or less͒ have resulted in sufficiently large undercooling to form glassy Te-Cu alloys in the form of a fine droplet emulsion. 6 To achieve a deeply undercooled liquid state, high-temperature high-vacuum electrostatic levitation 7 has been developed as a containerless process which eliminates the need for a melt containment vessel that often initiates heterogeneous nucleation. Recently, the undercooled melt of a Zr-Ti-Cu-Ni-Be alloy has been found to exhibit extremely high thermal stability. 8 Containerless electrostatic levitation processing was applied to the present investigation to further study the undercooling behavior of the liquid alloy. Information obtained from the present analysis has been coupled with the results from an earlier study of the glass forming ability of this alloy to provide a clearer understanding of the necessary conditions for glass formation ͑e.g., critical cooling rate͒ as well as proper thermal treatment of the melt required to suppress heterogeneous nucleation of crystals.Alloy ingots with the nominal composition Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 were prepared from a mixture of elements of purity ranging from 99.5% to 99.9% by induction melting on a water cooled silver boat under a Ti-gettered argon gas atmosphere. Prior to processing, the hightemperature high-vacuum electrostatic levitator ͑HTHVESL͒ was evacuated to an ultimate vacuum of 6.7ϫ10 Ϫ3 mPa. Sample heating was provided by a 1 kW UV-rich high pressure xenon arc lamp ͑ILC, model LX 1000CF͒. During the melting and so...

High temperature high vacuum electrostatic levitation was used to determine the complete timetemperature-transformation ͑TTT͒ diagram of the Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 bulk metallic glass forming alloy in the undercooled liquid state. This is the first report of experimental data on the crystallization kinetics of a metallic system covering the entire temperature range of the undercooled melt down to the glass transition temperature. The measured TTT diagram exhibits the expected ''C'' shape. Existing models that assume polymorphic crystallization cannot satisfactorily explain the experimentally obtained TTT diagram. This originates from the complex crystallization mechanisms that occur in this bulk glass-forming system, involving large composition fluctuations prior to crystallization as well as phase separation in the undercooled liquid state below 800 K. © 1996 American Institute of Physics. ͓S0003-6951͑96͒03308-8͔The synthesis of bulk metallic glasses using low cooling rates was first achieved in the Ni-Pd-P alloy system. 1,2 Recently, after the discovery of several families of multicomponent alloys such as La-Al-Ni, 3 Zr-Al-Cu-Ni, 4 and Zr-Ti-Cu-Ni-Be, 5 bulk glass formation became a common phenomena. The undercooled liquid state of the latter alloy possesses an extremely high thermal stability with respect to crystallization. This lends the material to experimental study of its undercooling and solidification behavior. The containerless high-temperature high-vacuum electrostatic levitation ͑HTHVESL͒ processing technique 6 permits comprehensive studies of thermophysical properties in deeply undercooled liquid metals. By applying the HVHTESL technique to the Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 alloy, for example, the authors found that proper thermal treatment during solification results in the ''self-fluxing'' of the melt, allowing it to successfully undercool down to the glass transition with cooling rates of about 1 K/s. 7 Detailed thermodynamic studies were made to explain the stability of the undercooled liquid. 8 Thermophysical properties, such as specific heat capacity and total hemispherical emissivity, over the whole range of the undercooled liquid have been determined. 9 Due to the limited glass-forming ability of earlier alloys, the acquisition of basic data on crystallization kinetics in the deeply undercooled melts has not been previously possible. However, the application of the HVHTESL technique to the Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 alloy offers a new opportunity to study the crystallization kinetics in the entire undercooled melt down to the glass transition. In this letter, we report the experimental of the TTT diagram, which describes the occurrence of the crystallization events as a function of isothermal annealing time and temperature in the undercooled liquid. For the first time, we experimentally define the complete TTT diagram for the crystallization of an alloy for the whole range of the undercooled liquid, i.e., from the melting point down to the glass trans...

High-temperature high-vacuum electrostatic levitation ͑HTHVESL͒ and differential scanning calorimetry ͑DSC͒ were combined to determine the hemispherical total emissivity ⑀ T , and the specific heat capacity c p , of the undercooled liquid and throughout the glass transition of the Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 bulk metallic glass forming alloy. The ratio of c p /⑀ T as a function of undercooling was determining from radiative cooling curves measured in the HTHVESL. Using specific heat capacity data obtained by DSC investigations close to the glass transition and above the melting point, ⑀ T and c p were separated and the specific heat capacity of the whole undercooled liquid region was determined. Furthermore, the hemispherical total emissivity of the liquid was found to be about 0.22 at 980 K. On undercooling the liquid, the emissivity decreases to approximately 0.18 at about 670 K, where the undercooled liquid starts to freeze to a glass. No significant changes of the emissivity are observed as the alloy undergoes the glass transition. © 1995 American Institute of Physics.The hemispherical total emissivity ⑀ T , which is the ratio of energy emitted by a material at a temperature T with respect to a blackbody at the same temperature, has been measured for several solid metals, 1-4 alloys, 5 and semiconductors. 6 However, there is a lack of emissivity data on liquid metals and only recently first results were reported for undercooled metallic liquids. 7 Lately, new multicomponent alloy systems have been found such as La-Al-Ni, 8 Zr-Al-Cu-Ni, 9 and Zr-Ti-Cu-Ni-Be 10 exhibiting an extraordinary thermal stability of the undercooled liquid with respect to crystallization. Cooling rates of less than 100 K/s are usually sufficient to suppress nucleation of crystalline compounds and thus form a bulk metallic glass in these alloy systems. For the particular Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 alloy we even showed that the melt could be undercooled more than 350 K below the liquidus temperature, T liq ϭ993 K, applying cooling rates lower than 2 K/s. The melt then undergoes the glass transition. 11 This deep undercooling of a liquid alloy melt without crystallization was achieved in a hightemperature high-vacuum electrostatic levitator ͑HTH-VESL͒. It offers the opportunity to investigate thermophysical properties of undercooled metallic melts in regions which have not been accessible so far. In this letter the hemispherical total emissivity ⑀ T , and the specific heat capacity c p , of the Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 alloy are determined in the undercooled liquid state as well as in the glass transition region by measuring c p /⑀ T as a function of temperature in the HTHVESL and combining the data with specific heat capacity measurements in a differential scanning calorimeter ͑DSC͒.Amorphous alloy ingots with a composition Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 were prepared from a mixture of the elements by induction melting. Pieces of typically 40 mg were remelted in a radio frequency field to...