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Low-Temperature Amplitude-Dependent Internal Friction of Dislocation-Point Defect Systems

To investigate the interaction between a dislocation and an impurity atom at low temperatures, amplitude-dependent internal friction (ADIF) measurements are made at 1.6 - 30 K by using pure Al crystals, into which are introduced a single kind of impurities, i.e., 100 at ppm Zn, 50 at ppm Ag, 25 at ppm Mg and 20 at ppm Cu, respectively. The following common features are found for all crystals: The applied stress amplitude σ0 under a constant ADIF varies as - T2/3 at lower temperatures, i.e., σ0/σ0(T=0)≧0.65, where σ0(T=0) is the extrapolated value; and the temperature dependence at σ0/σ0(T=0)≦0.87 is explained satisfactorily by a simple potential where the Cottrell type one is modified. From these results, the expected behavior on the dislocation motion at very low temperatures is briefly discussed.