By utilizing ultrasonic annealing at a temperature below (or near) the glass transition temperature Tg, we revealed a microstructural pattern of a partially crystallized Pd-based metallic glass with a high-resolution electron microscopy. On the basis of the observed microstructure, we inferred a plausible microstructural model of fragile metallic glasses composed of strongly bonded regions surrounded by weakly bonded regions (WBRs). The crystallization in WBRs at such a low temperature under the ultrasonic vibrations is caused by accumulation of atomic jumps associated with the beta relaxation being resonant with the ultrasonic strains. This microstructural model successfully illustrates a marked increase of elasticity after crystallization with a small density change and a correlation between the fragility of the liquid and the Poisson ratio of the solid.

The cavitation noise in the ultrasonic vibration system was found to be influenced by the size of microparticles added in water. The SiO2 microparticles with the diameter smaller than 100 μm reduced the cavitation noise, and the reason was attributed to the constrained oscillation of the cavitation bubbles, which were stabilized by the microparticles.

The frequency and temperature dependence of the ultrasonic attenuation in glassy Pd–Si-based alloys has been measured. In all compositions, the room-temperature attenuation varies as the square of frequency. A remarkably low loss of 0.06 dB/μsec at 100 MHz for longitudinal waves is observed in alloys containing silver, a loss equal to the lowest value reported for fused silica. Below 300 K, the attenuation in Pd0.775Ag0.06Si0.165 shows a broad peak at about 25 K. This behavior is similar to that noted in chalcogenide glasses. The estimated electronic contribution to attenuation is too small to account for measured values. Present data are insufficient to ascertain what causes this relaxation peak. It may be related to the excess specific heat previously observed in these alloys at low temperatures.