A. Le Moulec

In situ crystallization of Zr55Cu30Al10Ni5 bulk glass forming from the glassy and undercooled liquid states using synchrotron radiation

Abstract Real-time detection of crystal nucleation and growth in amorphous Zr 55 Cu 30 Al 10 Ni 5 was performed for the first time. The experiments were performed at the European Synchrotron Radiation Facilities (ESRF) using monochromatic beam with energy of 90 keV corresponding to a X-ray wavelength of 0.137 A. Full X-ray spectra in transmission were obtained every 3 s. Crystallization was monitored both during heating of the amorphous alloy and during cooling of the liquid alloy to detect differences in the nucleating crystalline phases. We found that crystallization of the amorphous phase occurs via initial nucleation and growth of a metastable phase that transforms to equilibrium tetragonal Zr 2 Cu before melting. However, no trace of nucleation of the metastable phase was obtained during cooling of the liquid alloy from above T m and Zr 2 Cu formed directly from the liquid.

Processing of bulk glass forming alloys in high energy synchrotron beams

Abstract X-ray diffraction is a convenient method for probing the structure of matter at the atomic and nanometric levels. When applied to metals and alloys, powerful diffractometers require acquisition times τ a of the order of 10 2 to 10 3 seconds for a pattern with good statistics over the full scattering vector (diffraction angle) range. Diffraction studies of structural transformations occuring on a time scale of τ t can only be effective if τ a ⪡ τ t to allow the acquisition of several spectra during the transformation. The availability now, of high energy, high intensity monochromatic light from synchrotron sources has reduced the acquisition times by several orders of magnitude. In this work we review the use of such beams for real-time probing of rapidly occurring phenomena in bulk metallic glass-forming alloys.

Glass Transition Tg, and Quenched-In Free Volume in Bulk Metallic Glasses Measured by X-Ray Diffraction

In this work we show that through thermal expansion αth measured by real-time diffraction using synchrotron light in transmission, the “glass transition Tg” and for the first time, the “quenched-in free volume” can be quantitatively measured in bulk metallic glasses. This was impossible previously as metallic glasses with crystallisation temperature Tx near Tg crystallized during real-time diffraction experiments. This limitation does not hold for newly developed bulk metallic glasses (BMGs) with large supercooled regions ∆T = Tx-Tg. Under such conditions, the variation, ∆αth, of the volume coefficient of thermal expansion has been measured by diffraction near Tg for a number of bulk metallic glasses. A clear ∆αth has been detected in the same glass transition temperature range of ∆Cp measured by DSC calorimetry in particular for Pd-based, Zrbased and Hf-based bulk glasses. The directly measured quenched-in free-volume content Vf is reported here for the first time is found, as expected, to depend on the quench rate and anneals out just below Tg.

Short-Range Order in Pd42.5Cu30Ni7.5P20 Bulk and Ribbon Metallic Glasses

In this work the structural changes in the Pd42.5Cu30Ni7.5P20 bulk and ribbon metallic glasses near the glass transition temperature have been investigated by a monochromatic high flux, high energy beam from the European Synchrotron Radiation Facilities (ESRF). Structure factors (SFs) and pair distribution functions (PDFs) were calculated using the measured intensities at different temperatures. We used a regularisation algorithm in order to calculate PDFs. Regularisation was carried out firstly by direct smoothing of the experimental SFs using their expansion in terms of odd Hermit functions (which are orthogonal in (0,∞) interval) and secondly by Fourier transformation of the smoothed function. Introduction Real-time diffraction studies of phenomena occurring on a time scale of τt can only be effective if acquisition time τa<<τt. When applied to metals and alloys, powerful X-ray diffractometers and neutron sources require acquisition times τa of the order of 10 to 10 seconds for a pattern with good statistics over the full scattering vector (diffraction angle) range. Previously, the problem for metallic glasses was that being unstable near the glass transition temperature Tg, they crystallized during such diffraction experiment. This limitation does not occur in the more recently developed bulk metallic glasses (BMGs) [1-5] with large supercooled regions ∆T=Tx-Tg below the crystallization onset temperature. Furthermore, the availability of high energy, high intensity monochromatic light from synchrotron sources has reduced the acquisition times by several orders of magnitude. The condition τa<<τt is therefore now satisfied for conducting in-situ diffraction experiments across the range below and above Tg in BMGs as was recently demonstrated [6, 7]. For example, it has recently been shown for the first time that precise measurements of the positions of the diffraction maxima for BMGs can be used to detect Tg by diffraction [8]. In the present paper we examine diffraction patterns below and above Tg for Pd42.5Cu30Ni7.5P20 bulk and ribbon metallic glasses and calculate the corresponding pair distribution functions. Experimental Technique The diffraction patterns were obtained in transmission [9-11] with a high intensity high energy monochromatic beam in order to continuously follow the evolution of the glassy alloy during heating at a rate dT/dt ~0.66 K/s from the glassy state across Tg (~ 550 K) to the superheated liquid state. The radiation on the ID11 beam line of the ESRF was tuned to the selected photon energy of 96 keV corresponding to an X-ray wavelength of about 0.12915 Å using a double crystal nitrogencooled silicon monochromator. Bulk metallic samples were prepared by slow cooling of a pre-fluxed liquid metal in a quartz container. Ribbons were prepared by melt spinning under argon gas. For the in-situ diffraction experiments, samples were placed into pyrex capillary tubes with 10 μm wall thickness and sealed Journal of Metastable and Nanocrystalline Materials Online: 2004-08-01 ISSN: 2297-6620, Vol. 22, pp 65-70 doi:10.4028/www.scientific.net/JMNM.22.65