The amplitude-dependent internal friction of 6N-purity Al and dilute (20 to 100ppm) Al alloys was measured between 2 and 240K. Two universal properties were found in the temperature dependence of the required stress amplitude for a constant decrement. At relatively low temperatures (or high stress amplitudes), the decrease in the stress with increasing temperature was proportional to T2/3, down to 65% of the stress for 0K, and then deviated from the T2/3 dependence. It was suggested that the elementary process was due to the unpinning of a dislocation from a single solute atom. The interaction potential was successfully deduced from this region (above 40% of the stress at 0K). At relatively high temperatures (or at stresses of less than 40% of that for 0K), it was found - for the first time - that the stress changed in proportion to T−1 for dilute Al alloys but not for a pure Al crystal. It was proposed that the elementary process in dilute alloys involved the simultaneous unpinning of a dislocation from several solute atoms.

Simultaneous Breakaway of a Dislocation from Several Pinning Points. T.Kosugi: Materials Science and Engineering A, 2004, 370[1-2], 230-3