Abstract
The internal friction of metal films was investigated by means of the torsion pendulum method. The films were produced by the evaporation on glass substrates which were covered with thin film of sodium chloride. They were removed from the substrates by immersing into water.
It was found that the free decay oscillation curve of bismuth films has a very high damping coefficient and also has such a form that an exponential decay curve is superposed on an ordinary cyclic decay curve symmetrical about the base axis of time. The initial value of the exponential decay part deviates to the initially twisted direction and the deviation is found to increase and then saturate with increasing holding time of the films in the initially twisted state. Other metal films which include Ag, Al, Au, Cu, 55 Cu-Ni and Sn films have no such a remarkable asymmetry as observed on bismuth films. It is shown that the behavior of bismuth films which is given initial displacement is satisfactorily explained by a model composed of the standard linear solid and a mass hanged under that.
The value of Q−1 of bismuth films was determined as a function of temperature for two frequencies. The activation energy obtained from the peak shift is 6×103 cal/mol. This value is close to the value of 5.5×103 cal/mol which is obtained from the temperature dependence of the critical holding time.
