On the possibility of the self-blocking of dislocations in various materials

Abstract

Experiments on heating without stress after a preliminary plastic deformation of bcc metals (armco Fe, Mo) have been carried out. The temperatures of deformation and heating were varied in wide limits. No transformations of dislocations from a curvilinear into a rectilinear blocked form were observed; i.e., no self-blocking of dislocations has been found in these bcc metals, in contrast to the previously investigated intermetallic compounds of the Ni3Al and TiAl type. A comparison of the behavior of dislocations in the bcc metals with that of single dislocations in TiAl has been performed. Using a previously suggested model, times that characterize the formation of kinks and their moving apart from one another have been introduced. It is shown that the change in the relationships between these times controls the changes in the shape of dislocations both during plastic deformation and upon heating in the absence of an external load. An analysis of the totality of experimental data obtained leads to a conclusion that it is the multivalley nature of the potential relief that plays the determining role in blocking and self-blocking of dislocations. Since the potential relief in bcc metals is single-valley, neither self-blocking of dislocations nor anomalous behavior of the yield stress has been observed. The problem of what equilibrium structures of the single-dislocation core in TiAl correspond to shallow and deep valleys and, also, what is the barrier that must be overcome for the passage between them, has also been considered.