Amplitude-Dependent Internal Friction and Microplasticity in Thin-Film Materials

Abstract
Internal friction in aluminum thin films on silicon substrates has been measured between 180 and 360 K as a function of strain amplitude. The amplitude dependence of internal friction in the aluminum films has been evaluated from the data on the film-substrate composite and further converted into the plastic strain of the order of 10^-9 as a function of the effective stress on dislocation motion. The microplastic stress-strain curves thus obtained for the aluminum films tend to shift to a higher stress with decreasing film thickness and also with decreasing temperature. It is concluded that the microflow stress at a constant level of the plastic strain varies inversely with the film thickness at all the temperatures examined.