Dislocation pinning and depinning in electron irradiated molybdenum

Abstract

The internal friction of electron irradiated molybdenum has been studied between 45 and 330°K. Dislocation pinning occurred between 50 and 70°K and is interpreted as arising from the movement of interstitials to the dislocations. A broad stage of depinning occurred above 90°K, and the friction recovered to its pre-irradiation value after a few hours anneal at 330°K. The depinning is thought to be due to the release of the interstitial pinning points from dislocations with different binding energies. The correlation of the pinning with the electrical resistivity annealing data and the difficulties of interpretation are similar to those found in the f.c.c. metals. The apparent value of the displacement energy measured was about 50 ev. This is much higher than the value of 37 ev found by Lucasson and Walker (1962). It may be that more energy is needed to form a widely separated interstitial vacancy pair than a close pair, and only interstitials from the former move to and pin dislocations.