Small-angle x-ray-scattering study of phase separation and crystallization in the bulk amorphousMg62Cu25

W. Liu

¹

,

William L. Johnson

²

,

Susanne Schneider

³

et al.

Abstract

We report on a small-angle x-ray-scattering ͑SAXS͒ and differential scanning calorimetry study of phase separation and crystallization in rapidly quenched amorphous Mg 62 Cu 25 Y 10 Li 3 alloy samples. Differential scanning calorimetry demonstrates the occurrence of crystallization and grain growth upon isothermal annealing of these samples at 135°C. The SAXS studies show the presence of large inhomogeneities even in the rapidly quenched as-prepared Mg 62 Cu 25 Y 10 Li 3 alloy that is attributed to phase separation in the undercooled liquid during the cooling process. After isothermal annealing at 135°C for longer than 30 min the samples exhibit a strong SAXS intensity that monotonically increases with increasing annealing time. During heat treatment, crystallization and growth of a nanocrystalline bcc-Mg 7 Li 3 phase occurs in the Y-poor and MgLirich domains. The initially rough boundaries of the nanocrystals become sharper with increasing annealing time. Anomalous small-angle x-ray-scattering investigations near the Cu K edge indicate that while Cu is distributed homogeneously in the as-prepared sample, a Cu composition gradient develops between the matrix and the bcc-Mg 7 Li 3 nanocrystals in the annealed sample. ͓S0163-1829͑99͒01018-8͔

Processing Routes, Microstructure and Mechanical Properties of Metallic Glasses and their Composites

“…[54,55] In this context it was found, that the stabilization of the quasicrystalline shortrange order strongly depends on the concentration of dissolved oxygen in the melt. [56,57] (c) Two phase amorphous-composites: Such composites can be obtained by liquid phase separation during solidification, which has already been reported a long time ago in PdAu-Si [80] and in Pd-Ni-P. [81] Phase separation occurs in some metallic glasses during annealing in the supercooled liquid region prior to crystallization, as observed for Vitreloy 1 (Zr 41.25 Nb 13.75 Cu 12.5 Ni 10 Be 22.5 ) [82] and for Mg 62 Cu 25 Y 10 Li 3 ribbons [83] or during casting. [84][85][86][87][88][89][90][91][92][93] This behavior can be explained either as a precursor step before primary crystallization [82] or as a result of a positive enthalpy of mixing between the constituent elements.…”

Energy Renormalization and Damping of Long-Wavelength Phonons in Amorphous Solids

“…Figure 1 depicts a collection of SANS and SAXS data (taken from [14][15][16] and references in [11]) in a log-log plot of SðkÞ vs. k together with model functions (15) with n ¼ 3 and n ¼ 4. The plot outlines Fig.…”

“…The plots for amorphous SiO 2 , the amorphous polymers PMMA, PET, PS, PE, Polycarbonate, the epoxy resins EPON 828 TETA, EPON 828 NMA, EPON 812, measured by SAXS, are taken from references in [11]. In the case of rapidly quenched amorphous Mg 62 Cu 25 Y 10 Li 3 alloy, measured by SAXS, the data of the as-prepared sample are presented (taken from [16]). In the SANS-measured 10 mol% Cu-Al 2 O 3 the formation of a-Al 2 O 3 has occured [14].…”

“…Renormalization RðqÞ (cf. (16) and Table 3) vs. q=q D for the model functions for the static structure factor (cf. (15)) with n ¼ 4; .…”

Glass transition, crystallization kinetics and pressure effect on crystallization of ZrNbCuNiBe bulk metallic glass

“…[1][2][3] It is found that the crystallization process is sensitive to alloy composition, 4 applied pressure, [5][6][7][8][9][10] annealing temperature, 11,12 and heating rate 13 so on. Schroers et al 13 has proved that a rate of about 200 K/s upon heating can avoid any crystallization events in the Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 bulk metallic glass.…”