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

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Results of calorimetric, differential thermal analysis, and structural measurements are presented for a series of bulk metallic glass forming compositions in the Zr-Ti-Cu-Ni-Be alloy system. The calorimetric data for five alloys, prepared along the tie line between phase separating and nonphase separating compositions, show that the transition from phase separating to nonphase separating behavior is smooth. The bulk glasses near the center of the tie line exhibit large supercooled liquid regions: ⌬TϷ135 K, the largest known for a bulk metallic glass. © 1999 American Institute of Physics. ͓S0003-6951͑99͒01734-9͔There are a number of multicomponent bulk metallic glass ͑BMG͒ forming alloy systems, e.g., La-Ni-Al, 1 Zr-Al-Cu-Ni, 2 Zr-Ti-Cu-Ni-Be, 3 and Zr-Ti-Cu-Ni. 4 The Be-containing bulk glass Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 ͑Vit 1͒ exhibits an exceptional glass forming ability ͑GFA͒ and thermal stability with respect to crystallization. The liquidstate viscosity of the Be-BMG alloys is Ϸ two orders of magnitude higher than in pure metals or alloys, typically (Be-BMG)Ϸ5 poise. 5 The high melt viscosities of the Be-BMG compositions yield very sluggish crystallization kinetics in the supercooled liquid region ͑SLR͒. The crystallization behavior of Vit 1 has been determined by electrostatic levitation ͑ESL͒ and calorimetric methods. 6,7 These results, when combined with the results of small angle neutron scattering ͑SANS͒ measurements conducted by Schneider, Johnson, and Thiyagarajan show that primary crystallization is preceded by phase separation in the SLR. 8 This phase separation process shows many of the features of a spinodal decomposition, with a spinodal temperature of Ϸ 671 K. The decomposition process is followed by the nucleation of fcc nanocrystals on a length scale correlated with the spinodal wavelength, s Ϸ14 nm. The bulk glass Zr 46.75 Ti 8.25 Cu 7.5 Ni 10 Be 27.5 ͑Vit 4͒ also exhibits an excellent GFA. This alloy exhibits little phase separation prior to crystallization. To elucidate this behavior, results of thermophysical property measurements are presented for compositions along the tie line between the compositions of Vit 1 and Vit 4, the phase separating and nonphase separating alloys, respectively. The thermophysical property data show that through controlled changes in alloy composition the GFA may be altered drastically. The experimental data are related to the known features of the Vit 1 time-temperaturetransformation ͑TTT͒ diagram determined from the ESL measurements.The details of the methods used to prepare the master alloys are described elsewhere. 9 The tie-line alloy compositions were prepared in the form of thin strips, 1ϫ5ϫ Ϸ25 mm ͑thickness by width by length͒, by injection casting into a Cu metal mold. The specimen compositions prepared along the tie line from Vit 1 to Vit 4, labeled Vit 1, 1͑a͒, 1͑b͒, 1͑c͒, and 4, respectively, are presented in Table I. The nominal compositions are used in this letter. The strategy employed in this alloy series involves incrementally changin...

mentioning

confidence: 98%

Large supercooled liquid region and phase separation in the Zr–Ti–Ni–Cu–Be bulk metallic glasses

Hays¹,

Kim²,

Johnson³

1999

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“…In this diagram, the time at which a heat release is detected during isothermal annealing is plotted as a function of temperature. Additionally, data obtained by containerless electrostatic levitation ͑ESL͒ experiments 12 are shown in Fig. 1 as open circles.…”

Section: ͓S0003-6951͑99͒05118-9͔mentioning

confidence: 99%

“…Isothermal crystallization studies are performed on Zr 41 Ti 14 Cu 12 Ni 10 Be 23 melts between the liquidus and the glass transition temperature. The resulting time-temperature-transformation diagram is in good agreement with the data obtained from containerlessly processed samples.…”

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confidence: 99%

Continuous refinement of the microstructure during crystallization of supercooled Zr41Ti14Cu12Ni10Be23 melts

Schroers

Busch

Masuhr

et al. 1999

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Isothermal crystallization studies are performed on Zr 41 Ti 14 Cu 12 Ni 10 Be 23 melts between the liquidus and the glass transition temperature. The resulting time-temperature-transformation diagram is in good agreement with the data obtained from containerlessly processed samples. The various solidification products are examined by electron microprobe. The investigations reveal the morphology and typical length scale of the microstructure as well as the primarily solidified phases after crystallizing at different degrees of undercooling. The typical length scale decreases continuously with increasing supercooling over five orders of magnitude. The number density of nuclei during primary crystallization is estimated from the microstructure. The results are discussed within several models, such as steady-state nucleation, spinodal decomposition, and a nonpolymorphic nucleation model. © 1999 American Institute of Physics. ͓S0003-6951͑99͒05118-9͔Recently discovered multicomponent metallic alloys 1,2 exhibit excellent glass-forming ability. The critical cooling rate for glass formation of the Zr 41 Ti 14 Cu 12 Ni 10 Be 23 ͑Vit 1͒ alloy, for example, is 1 K/s. 3 The high thermal stability of melts of this bulk metallic glass against crystallization leads to an experimentally accessible time and temperature window to investigate isothermally the transformation behavior from the supercooled ͑undercooled͒ liquid into the crystalline phases. It was shown that the Vit 1 alloy is very robust with respect of heterogeneous surface nucleation. 4 Therefore, processing of these samples in graphite crucibles is possible.Several investigations have been performed that correlate the microstructure of metallic alloys with the nucleation and growth behavior ͑see, e.g., Refs. 5 and 6͒. Since the composition of Vit 1 is close to a deep eutectic, nucleation of crystalline phases from the homogeneous multicomponent melt is suppressed to a great extent. Therefore, it is somewhat surprising that Vit 1 crystallize at low temperatures, in the vicinity of the glass transition temperature T g , from the amorphous state, into a nanocrystalline microstructure. Explanations, such as extremely high heterogeneous nucleation rates and quenched-in nuclei 7 were applied to describe the high crystal density. Alternative processes such as phase separation in the supercooled liquid prior to crystallization 8,9 or a homogeneous nucleation model, which take into account linked fluxes of interface attachment and diffusion in the liquid to the cluster neighborhood, 10 were used to explain the high number density of nuclei.This letter focuses on a detailed microstructure analysis of Vit 1 samples solidified after different isothermal annealing times at distinct levels of undercooling.Amorphous samples were prepared by arc melting the constituents ͑purity ranging from 99.5% to 99.995%͒ in a titanium-gettered argon atmosphere. The samples were introduced into the graphite crucibles that were inductively heated in a titanium-gettered argon atmosphere. The max...

“…The reported thermodynamic studies include the measurements of the specific heat, 2 hemispherical total emissivity, 3 viscosity, 4 and atomic diffusion coefficient. 5 The kinetic studies include the evaluations of the time-temperature-transformation ͑TTT͒ curve 6 and the Gibbs free energy change on crystallization. 2 In this letter, we report the results of specific volume measurements of the Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 alloy in the liquid, glass, and crystalline states, and the associated analyses.…”

mentioning

confidence: 99%

Specific volumes of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 alloy in the liquid, glass, and crystalline states

Ohsaka

Chung

Rhim

et al. 1997

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The specific volumes of the Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 alloy as a function of temperature, T, are determined by employing an image digitizing technique and numerical calculation methods applied to the electrostatically levitated spherical alloy. The linear fitting of the volumes of the alloy in the liquid, V l , glass, V g , and crystalline V c , states in the temperature ranges shown in parentheses are V l (T)ϭ0.1583ϩ8.877ϫ10 Ϫ6 T(cm 3 /g) (700-1300 K);V g (T)ϭ0.1603ϩ5.528ϫ10 Ϫ6 T (400 -550 K);V c (T)ϭ0.1583ϩ6.211ϫ10 Ϫ6 T(400-850 K). The average volume thermal expansion coefficients within the temperature ranges are determined to be 5.32, 3.39, and 3.83ϫ10 Ϫ5 ͑1/K͒ for the liquid, glass, and crystalline states, respectively. © 1997 American Institute of Physics. ͓S0003-6951͑97͒03906-5͔A family of the Zr-Ti-Cu-Ni-Be alloys which exhibit an exceptional glass formability has provided a rare opportunity to study the thermophysical properties and phase transition kinetics of glass forming metallic alloys in a deeply undercooled liquid state and the glass transition region. The critical cooling rate of the alloys for glass formation is of the order of Ϫ10 K/s or less, 1 which is sufficiently slower than experimental time scales of some measurements. The reported thermodynamic studies include the measurements of the specific heat, 2 hemispherical total emissivity, 3 viscosity, 4 and atomic diffusion coefficient. 5 The kinetic studies include the evaluations of the time-temperature-transformation ͑TTT͒ curve 6 and the Gibbs free energy change on crystallization. 2 In this letter, we report the results of specific volume measurements of the Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 alloy in the liquid, glass, and crystalline states, and the associated analyses. The specific volume is a fundamental property and it is indispensable to study the nature of phase transitions, specifically the glass transition for the present alloy.Samples of typically 40 mg ͑approximately 2.2 mm in diameter͒ were separated from a bulk molten alloy whose nominal composition was Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 in at. %, and were formed to make spheres in an arc melter. The samples were then weighed and placed individually in a high temperature electrostatic levitator 7 which was operated in a high vacuum. Once a sample was levitated, it was heated above the liquidus temperature, T L ϭ993 K 1 , with a high intensity xenon arc lamp. Cooling of the sample was achieved by natural radiative heat loss to the surroundings. During the experiment, the sample temperature was monitored by a single color pyrometer with a preset emissivity. Also, the images of the levitated sample were stored on videotape. The specific volumes were determined from these images by employing an image digitizing technique and numerical calculation methods. The detailed description of the volume measurement technique has been reported elsewhere. 8 Figure 1 shows a typical thermogram of a sample on cooling when the xenon lamp is completely shut off. The tempe...