Climb of Orowan loops in an overaged Al–Li alloy

The annihilation process of Orowan loops formed around coherent δ′-particles in overaged Al–Li alloy single crystals was examined using compression tests and transmission electron microscopy. Softening on annealing following work hardening was inversely proportional to the fourth power of the particle size, indicating that the Orowan loops climb and disappear by pipe diffusion through their cores. The activation energy for the pipe diffusion was approximately 0.75 eV. Direct evidence was given for the climb and loss of Orowan loops on annealing. The decrease in the loop density was in good agreement with the macroscopic softening behavior. The mechanism of the dynamic softening was found to be the same as that of the static softening process.