Title

Transformations in glass-forming liquid alloys and bulk metallic glasses studied by real-time diffraction using high-energy synchrotron radiation

Transformations in glass-forming liquid alloys and bulk metallic glasses studied by real-time diffraction using high-energy synchrotron radiation

Authorship

YAVARI, ALAIN REZA; INOUE, AKIHISA; VAUGHAN, GAVIN; KVICK, AKE; FILHO, WALTER JOSÉ BOTTA

YAVARI, ALAIN REZA

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INOUE, AKIHISA

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VAUGHAN, GAVIN

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KVICK, AKE

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FILHO, WALTER JOSÉ BOTTA

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DOI

10.5151/2594-5327-2567

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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, conventional diffractometers require acquisition times τₐ of the order of 10² to 10³ seconds for a pattern with good statistics over the full scattering vector (diffraction angle) range. However, diffraction studies of structural transformations occurring on a time scale of τₜ can only be effective if τₐ ≪ τₜ 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. For undercooled liquid alloys and metallic glasses, the problem remained that above T₉, they crystallize rapidly during real-time diffraction experiments but this limitation is avoidable for bulk glass-forming alloys with large supercooled regions ΔT = Tₓ–T₉ where the crystallisation temperature Tₓ can be some 100 K above the glass transition at T₉. A variety of transformations in bulk glass-forming alloys are being detected using high energy, high flux monochromatic light from synchrotron source and will be reported in this work. These include homogeneous crystal nucleation from the glass, heterogeneous crystal nucleation from the undercooled liquid alloys, quasicrystallisation, in-the-beam amorphisation, formation of crystallites on fracture surfaces and the measurement of variation of αₜₕ, the volume coefficient of thermal expansion near T₉ to be compared to that of the specific heat ΔCₚ.

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, conventional diffractometers require acquisition times τₐ of the order of 10² to 10³ seconds for a pattern with good statistics over the full scattering vector (diffraction angle) range. However, diffraction studies of structural transformations occurring on a time scale of τₜ can only be effective if τₐ ≪ τₜ 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. For undercooled liquid alloys and metallic glasses, the problem remained that above T₉, they crystallize rapidly during real-time diffraction experiments but this limitation is avoidable for bulk glass-forming alloys with large supercooled regions ΔT = Tₓ–T₉ where the crystallisation temperature Tₓ can be some 100 K above the glass transition at T₉. A variety of transformations in bulk glass-forming alloys are being detected using high energy, high flux monochromatic light from synchrotron source and will be reported in this work. These include homogeneous crystal nucleation from the glass, heterogeneous crystal nucleation from the undercooled liquid alloys, quasicrystallisation, in-the-beam amorphisation, formation of crystallites on fracture surfaces and the measurement of variation of αₜₕ, the volume coefficient of thermal expansion near T₉ to be compared to that of the specific heat ΔCₚ.

Keywords

glass-forming liquid alloys, bulk metallic glasses, synchrotron radiation

glass-forming liquid alloys, bulk metallic glasses, synchrotron radiation