Friction mechanism of dislocation motion in icosahedral Al-Pd-Mn quasicrystals

Results from the literature and unpublished ones of the present authors are summarized which are relevant to the mechanisms governing the mobility of dislocations in icosahedral Al-Pd-Mn quasicrystals. These results concern m acroscopic deformation tests, conventional transmission electron microscopy , in situ straining experiments in a transmission electron microscope, and computer simulation experiments. These experiments can best be interpreted by assuming that the dislocation motion is controlled by the thermally acti vated overcoming of Mackay-type clusters. The present paper gives an estima te of the activation volume of this process. It turns out that the activati on volume of overcoming the clusters individually is one order of magnitude smaller than the experimentally observed one. The experimental observation s can be interpreted in a consistent way in terms of the Labusch-Schwarz th eory of solution hardening in crystals, which considers the interpenetratin g clusters as 'extended' obstacles, a number of which are surmounted collec tively. Some implications of this new model are discussed.