DISLOCATION DISSOCIATION IN THE INTERMETALLIC COMPOUND MOSI2

The identity of dislocations which contribute to plastic deformation o f polycrystalline MoSi2 when compressed at 1400-degrees-C has been det ermined using transmission electron microscopy. It has been confirmed that dislocations with Burgers vectors lying parallel to [100] and [11 1] are activated in response to the applied stress. In addition, the d eformation microstructure is characterized by the presence of networks containing dislocations with Burgers vectors parallel to [100], [110] and [111]. It has been shown that dislocations with Burgers vectors l ying parallel to [111] are dissociated. A simple explanation has been developed to account for the occurrence of dissociation of particular dislocations, and on the basis of this model the dissociation is repre sented by 1/2[111]-->1/4[111] + SISF + 1/4[111], where SISF stands for a superlattice intrinsic stacking fault. The SISF energy has been est imated from the separation of the partial dislocations to be about 261 mJ m-2. Other observations of the dissociation of dislocations in MoS i2 have been interpreted in terms of the model developed in the presen t work.