The Study Of The Cross-slip Mechanism Of Screw Dislocation In Nickel

Cross-slip of screw dislocation is an important motion of dislocation in a crystal and plays a key role in the plastic deformation of metals and semi-conductor materials.What we have done is to get the mechanism of the cross-slip in metal nickel.Firstly,we find two stationary states of the screw dislocation using Steepest descent method.Each stationary state has a screw dislocation in one specific slip plane.Secondly,we find the minimal energy path and energy barrier of the cross-slip from one slip plane to the other slip plane by the String method.Then we analyze the dislocation density of the important states on the minimal energy path to get the mechanism of the cross-slip.It is found that the mechanism of the cross-slip of the short screw dislocation without stress is affected by the relative position of the dislocation centers in the two stationary states.When the two dislocation centers are located at the same position,the cross-slip follows the Friedel-Escaig(FE)mechanism.When the two dislocation centers are located at some special positions relative to each other,the cross slip follows the Fleischer(FL)mechanism.Shear stress also has influence on the mechanism of the cross-slip.Applying a shear stress of 1.4Gpa on the crystal whose cross-slip follows FL mechanism under zero shear stress,we found that the cross-slip was promoted,still following FL mechanism.However,applying a shear stress of 1.7 Gpa on the crystal whose cross-slip follows FL mechanism under zero shear stress,we observed that the two dislocation partials constricted into a complete dislocation and the cross-slip followed the FE mechanism.