Metallic glass formation in highly undercooled Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 during containerless electrostatic levitation processing

Abstract

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...

Pronounced asymmetry in the crystallization behavior during constant heating and cooling of a bulk metallic glass-forming liquid

“…This diagram reveals a large asymmetry in the crystallization behavior between cooling from the stable melt and heating the amorphous sample. In agreement with previous results 10 we found a critical cooling rate for Vit 1 of about 1 K/s. However, the critical heating rate of approximately 200 K/s is about two orders of magnitude larger.…”

“…The critical cooling rate of Zr 41 Ti 14 Cu 12 Ni 10 Be 23 ͑Vit 1͒, studied in this work, is about 1 K/s. 10 In contrast, crystallization of amorphous Vit 1, previously investigated by differential scanning calorimetry ͑DSC͒ upon heating 11 could not be avoided up to the maximum heating rate of the DSC of 5 K/s and the critical heating rate has not been determined yet. The critical heating rate R h , the counterpart of the critical cooling rate upon heating, is the lowest rate an amorphous sample can be heated through the entire supercooled liquid region without crystallization.…”

The oxidation behavior of Cu42Zr42Al8Ag8 bulk metallic glasses

“…Among those BMG systems developed, Cu-Zr-based BMGs are among the most popular amorphous alloys that possess the advantages of low material cost, superior mechanical properties, and good glass-forming ability (GFA) [1][2][3][4][5]. Recent works reported that a Cu-Zr-based Cu 42 Zr 42 Al 8 Ag 8 alloy with large critical dimensions and high fracture strengths can be prepared by copper mold casting [6,7].…”

Experimental determination of a time–temperature-transformation diagram of the undercooled Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 alloy using the containerless electrostatic levitation processing technique

“…6,7 The sample temperature was measured using an E 2 T pyrometer ͑model 7000ET-1HR͒. Prior to the temperature measurements, the pyrometer was calibrated using the known eutectic temperature of 937 K. Initially, the molten sample was cooled radiatively to a predetermined temperature by blocking the heating source of a xenon arc lamp.…”

“…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.…”