The vacancies, lubrication agents of dislocation motion in aluminium

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Abstract
Measurements of the dynamic modulus and internal friction of ultra-high-purity aluminium were performed during irradiation with fast electrons at 5.7 K (or 60 K) and subsequent anneals, using a vibrating strip system. The salient result is that the introduction of point defects on the existing dislocations during irradiation at very low temperature, when the vacancies and self-interstitials are created are immobile, provokes a substantial decrease in the elastic modulus. This type of evolution does not originate in an elastic bulk effect but is instead shown to result from the lubrication of dislocation motion by the deposited defects. This finding substantiates the concept of an athermal lubrication mechanism proposed recently for the interpretation of cold-work results. Further insight into the nature of the defect species responsible for this lubrication has been attained by the realisation of irradiation and anneal sequences at different temperatures. It appears that, contrary to that which happens with self-interstitials, which are found to act as dislocation pinners, as is normally the case, the vacancies facilitate the motion of dislocations down to the lowest temperatures explored.