Computer simulation of dislocation unzipping at low temperatures
Abstract
Computer simulation was used to investigate the process of successive acts of dislocations surmounting neighboring point obstacles, known as the unzipping process. The statistical characteristics of unzipping were studied at low temperatures, when the process is most highly developed. Under these conditions we obtained histograms of the distribution of the number of obstacles, from which obstacles unpinned successively as an unzipping wave propagated along a dislocation line in either direction. These distributions are shown to depend on the dislocation length, i.e., on the number N¯ of obstacles on which the dislocation rests at any moment in its motion, and also to depend on the path traversed by the dislocation in the slip plane (through the simulation area); these distributions prove to be independent of the load. The unzipping wave displays a tendency to change direction several times without interrupting its motion, as a result of which there is an effect which we call a “zipper” or “zigzag.” It is established that in the motion of a long dislocation line the zigzags tend to cluster and this results in “active zones” replacing each other and the unzipping process is successively localized in them. Consequently the motion of an extended dislocation line at low temperatures proceeds in separate, alternating “tongues” instead of uniformly. The occurrence of unzipping is shown not to resemble the process of broadening of a double kink in any way.