Mutual annihilation of unlike dislocations by cross slip in ordered and disordered alloys

Abstract

Under the action of an external applied stress, unlike dislocations on parallel slip planes either pass one another, or cross slip or climb and annihilate each other. A detailed numerical analysis of cross slip of unlike screw dislocations was carried out and the conditions under which cross slip was more favorable compared to passing were determined in both ordered and disordered alloys for infinite straight dislocations. It was further shown that cross slip could preferentially occur near the vicinity of an unlike dislocation which acted as a source of internal stress. The presence of such internal stresses was found to reduce the energy barrier for cross slip to an extent that cross slip became spontaneous if the vertical separation between the unlike dislocations was below a critical value. The implication of this was that in the absence of any other internal stresses, the passing dislocation of separation less than the critical value could not be stable, and this critical separation set the limit for the strengthening that could be obtained by passing dislocations. The effects of the applied stress, and its orientation on the cross slip process have also been discussed in detail.