Junjun Huang

Internal friction of nanocrystalline silver

Low frequency internal friction and shear modulus of nanocrystalline silver were measured by both force vibration and free decay methods. The specimens were prepared by inert gas condensation and in situ warm compaction. The average grain size of the specimens was 52 nm. An internal friction peak was observed around 450 K. The activation energy of the peak was measured to be 0.88 (±0.1) eV, in agreement with that of grain boundary diffusion in silver. The internal friction peak is suggested to be associated with grain boundary relaxation.

Internal Friction Study of the Size-Dependent Melting of Pb Inclusions in an Al Matrix

Internal friction measurement was used to study the melting behavi our of elongated nanoscale Pb particles dispersed in an Al matrix. A single inte rnal friction peak, located at about 330°C, was observed. The onset temperature of this peak decreases with de creasing size of the Pb particles, which is consistent with the observation that the Pb par ticles show a melting point depression at small size.

Preparation and Internal Friction of Nanoscale Gallium Droplets

A simple but effective method, ultrasonic vibration, has been used to prepare the nanoscale (hereafter n-) Ga droplets. The n-Ga droplets with average particle size of about 60-80 nm in diameter dispersed in polystyrenes (PS) have been successfully obtained. The low frequency internal friction of solid polystyrenes containing n-Ga droplets was measured. We observed for the first time, that the internal friction peak caused by n-Ga droplets appears around 313 K. The peak shifts to higher temperature with increasing frequency, indicating a relaxation peak. It is suggested that the internal friction peak is associated with the relaxation of n-Ga droplets in the cavities of matrix under applied stress.