DYNAMIC DISLOCATION BEHAVIOR IN THE INTERMETALLIC COMPOUNDS NIAL, TIAL AND MOSI2

The dynamic behaviour of dislocations in NiAl, TiAl and MoSi2 on 'easy ' slip systems is studied by in situ straining experiments in a high-v oltage electron microscope. At elevated temperatures, the dislocations are smoothly bent as in NiAl and TiAl or sometimes show superkinks as in MoSi2, and they move in a viscous way. It is suggested that this d ynamic behaviour as well as the flow stress anomaly are connected with the formation of atmospheres around the dislocations. A model is prop osed assuming that the lowest energy configuration of a dislocation ma y require a certain number of antisite defects or other point defects in the dislocation core. This cloud of disordered structure may follow partly the moving dislocations to induce an additional friction, anal ogous to other diffusion controlled mechanisms. The view of atmosphere s controlling the dislocation mobility in intermetallics at elevated t emperatures is supported by measurements of the dependence of the stra in rate sensitivity on the strain rate itself. (C) 1998 Elsevier Scien ce Limited. All rights reserved.