MECHANICAL-PROPERTIES OF NANOCOMPOSITE GRANULAR METAL THIN-FILMS

The mechanical properties of nanocomposite Ag-Al2O3 and Fe-SiO2 granul ar metal films were investigated by low-load indentation and laser ult rasonic methods. A discontinuity in the rate of change of hardness as a function of metal volume fraction was observed near the percolation threshold for the metal. However, the sign of the rate of change was d ifferent for the two systems. It is suggested that this discontinuity was the result of a change in deformation mechanism as the percolation threshold for the softer phase was crossed. The elastic moduli of the Ag-Al2O3 films as measured by a laser ultrasonic technique displayed a rule-of-mixtures-type behavior, in contrast to nanoindentation measu rements that gave a peak in the apparent compliance. Indentation crack testing indicated that the toughness increased in the Ag-Al2O3 system when the metallic phase was introduced into the ceramic, but that the Fe-SiO2 system displayed unexpected and novel fracture behavior.