The effect of small pre-strain on the internal friction and modulus of high-purity molybdenum III. The temperature dependence of the modulus and the background damping

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Abstract
The temperature dependence of the internal friction and modulus have been measured at ∼500 Hz for annealed and lightly cold-worked molybdenum. The overall magnitude and shape of the damping curves can be accounted for by impurity pinning of dislocations, the differences between the curves arising from the known variation in purity of the samples and of the strain amplitude of measurement However, the frequency curves from different samples showed little similarity, the temperature variation being of either sign. This was investigated further in an annealed sample which was progressively pre-strained. It was found that the curves could be described in terms of a background frequency which rose to a maximum at about 150 K, on which was superimposed a number of discrete changes due to the modulus defects of β peaks which can also be identified in the damping curves. The anomalous rise in frequency associated with the background is attributed to the temperature-dependent drag of impurities on the dislocations, while the β peaks arise from the motion of impurites in specific sites near the dislocation.