Dislocation Damping in Dilute Lead Alloys

Internal friction has been measured at 4 kc/sec on single crystals as a function of strain amplitude, temperature, and composition in a series of Pb-In alloys, and one Pb-Sn alloy. The compositions are in the solid solution range. The results are discussed in terms of the theory of Granato and Lücke. There is a considerable measure of agreement between experiment and theory regarding the functional relationships between the various parameters. The binding energy of a dislocation to both In and Sn solute atoms is found to be 0.10 eV. There is some evidence that thermal unpinning may be playing a part. Some measurements on the effect of etching surface layers and of growth rate are described which demonstrate the structure sensitivity of internal friction.