THE INTERACTION OF DISLOCATIONS WITH COHERENT INCLUSIONS .1. PERFECT EDGE AND SCREW DISLOCATIONS

The passage of edge and screw dislocations through an array of spherical coherent obstacles is simulated for several obstacle sizes, array dimensions and misfit values, using computer techniques adapted from molecular dynamic methods. For small misfits, intersection of the obstacle takes place and the passing stress increases rapidly with increasing misfit. Above a critical misfit value, which varies with the size and separation of the obstacles, the passing mechanism changes to Orowan loop formation; the passing stress continues to increase with increasing misfit, but at a lower rate. It is found that there are two principal consequences of the obstacle stress field. Dipole-enhancing effects can lead to a reduction in the breaking angle to as low as 40-degrees from the near-90-degrees value expected for impenetrable obstacles, with a corresponding decrease in the passing stress. However, the coherency stresses also renormalize the obstacle geometry to increase their effectiveness as barriers to dislocation motion, causing an increase in the passing stress.