TY - JOUR
T1 - Structural inhomogeneity of metallic glass observed by ultrasonic and inelastic X-ray scattering measurements
AU - Ichitsubo, T.
AU - Matsubara, E.
N1 - Funding Information:
This work was supported by Grant-in-Aid for Scientific Research on the Priority Area Investigation of “Materials Science of Bulk Metallic Glasses” from the Ministry of Education, Science, Sports and Culture, Japan. We thank to Dr. Nishiyama for providing us with samples.
PY - 2009/9/15
Y1 - 2009/9/15
N2 - The structural stability of metallic glasses is frequently deteriorated under ultrasonic perturbation at relatively low temperatures, e.g., near the glass transition temperature Tg, even for thermally stable Pd- and Zr-based metallic glasses. By a mechanical spectroscopy analysis, it is suggested that such an instability, i.e., crystallization, is caused by atomic motions associated with the (slow) βrelaxation, that are resonant with the ultrasonic-strain field. Furthermore, such atomic motions below Tg are considered to occur at weakly bonded regions in a nanoscale inhomogeneous microstructure of glass, which was intuitively inferred from a partially crystallized microstructure obtained by annealing a Pd-based metallic glass just below Tg under ultrasonic perturbation. On this basis, we proposed a structural model of metallic glasses that consists of strongly bonded regions surrounded by weakly bonded regions. To reveal the validity of the model, we have also employed the inelastic X-ray scattering technique to measure the sound velocity of nanometer wavelength of longitudinal acoustic phonons. We have found in a completely frozen Pd-based metallic glass that the velocity of nanometer wavelength exceeds ultrasound velocity of millimeter wavelength, which suggests that elastically harder nanoscale regions exist in the glass matrix.
AB - The structural stability of metallic glasses is frequently deteriorated under ultrasonic perturbation at relatively low temperatures, e.g., near the glass transition temperature Tg, even for thermally stable Pd- and Zr-based metallic glasses. By a mechanical spectroscopy analysis, it is suggested that such an instability, i.e., crystallization, is caused by atomic motions associated with the (slow) βrelaxation, that are resonant with the ultrasonic-strain field. Furthermore, such atomic motions below Tg are considered to occur at weakly bonded regions in a nanoscale inhomogeneous microstructure of glass, which was intuitively inferred from a partially crystallized microstructure obtained by annealing a Pd-based metallic glass just below Tg under ultrasonic perturbation. On this basis, we proposed a structural model of metallic glasses that consists of strongly bonded regions surrounded by weakly bonded regions. To reveal the validity of the model, we have also employed the inelastic X-ray scattering technique to measure the sound velocity of nanometer wavelength of longitudinal acoustic phonons. We have found in a completely frozen Pd-based metallic glass that the velocity of nanometer wavelength exceeds ultrasound velocity of millimeter wavelength, which suggests that elastically harder nanoscale regions exist in the glass matrix.
KW - Bulk metallic glasses
KW - Elastic-constant fluctuation
KW - Inelastic X-ray scattering
KW - Phonon
KW - Positive dispersion
KW - Structural inhomogeneity
KW - Ultrasonic
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U2 - 10.1016/j.msea.2008.09.149
DO - 10.1016/j.msea.2008.09.149
M3 - Article
AN - SCOPUS:68949101208
VL - 521-522
SP - 236
EP - 242
JO - Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing
JF - Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing
SN - 0921-5093
ER -