Evidence for the dragging of point defects by dislocations from measurements of internal friction and modulus defect in irradiated and deformed molybdenum single crystals

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Abstract
The temperature dependence of the internal friction and modulus have been measured at about 500 Hz, at maximum strain amplitudes between 10-6 and 5 × 10-5 for annealed and cold-worked molybdenum. The effects of irradiation at 80 K and of annealing at 540 K have also been studied. All the results showed a background damping peak, the behaviour of which can be explained by the breakaway of dislocations from their pinning points using the Granato-Lücke theory. However, in some samples the behaviour of the resonant frequency was anomalous (frequency increasing with increasing temperature). The anomalous behaviour can be explained by the dragging of the point defects by the dislocations. The differences between the curves for the annealed and the cold-worked samples and the changes in irradiation have successfully been explained using the dragging model of Simpson and Sosin. A β peak seen at 150 K in a heavily cold-worked sample and a direct and an inverse-modulus defect seen at 150 K are all attributed to dragging of point defects trapped at kinks on the dislocations.