Impurity-kink interaction in the two-dimensional Frenkel-kontorova model

The dislocation gliding in crystals with impurities is investigated by computer simulations for the two­ dimensional Frenkel-Kontorova model. It is shown that the impurity-dislocation interaction can result in both the stimulation of the double-kink formation (which increases the dislocation mobility) and the trapping of moving kinks by the impurities with the following kink-antikink recombination (which slows down the dislo­ cation motion). The relative importance of these competing mechanisms depend mostly on the temperature as well as the type of impurity. Here we demonstrate that the presence of impurities can increase the dislocation velocity at low temperatures which leads to the solid solution softening. With increasing temperature, a transition from the solid solution softening to the solid solution hardening regime takes place. The dislocation mobility in crystal lattice periodic poten­ tial (the Peierls relief1) is one o f the key problems in solid state physics w hich still attracts considerable interest. The Peierls m echanism determines the dislocation mobility and, consequently, the mechanical behavior in covalent crystals (Si, Ge), bcc metals, and some intermetallic compounds. D e ­ spite considerable theoretical and experimental efforts2,3 the m icroscopic processes w hich are responsible for the disloca­ tion mobility in the Peierls relief are still a matter o f inten­ sive discussions.4-9 It is com m only accepted that the dislocation m otion in materials w ith high Peierls relief is accom plished by the propagation o f kinks along the dislocation line. It has been assumed that the kink density (and, consequently, the dislo­ cation mobility) is determined by the processes o f thermal fluctuation kink nucleation and o f the kink-antikink pair re­ combination. However, this very transparent but simplified concept is insufficient to describe the mechanical properties o f real materials2,3 where the impurity-kink interactions play a crucial role in the kink dynamics. Standard m odels consid­ ering the impurities just as centers o f kink-antikink recombi­ nation processes2 seem to be inadequate and do not explain accumulated experimental data.3,8,10,11 The contradictions b e­ tween the theoretically predicted equilibrium density o f the kinks and that estimated from experimental data initiates a hypothesis regarding the existence o f so-called "weak ob­ stacles" controlling the equilibrium density o f kinks, how ­ ever, the nature o f these obstacles has not yet been clarified.3 The effect o f impurities on the mechanical properties o f the crystals is rather com plex and cannot be reduced only to the deceleration o f kinks or to the initiation o f their annihi­ lation as it w as supposed in the earlier m odels.2 In particular, besides the w ell-know n effect o f the solid solution hardening (SSH) w hich is clearly connected with the pinning action o f the impurities on the dislocations, in som e cases the alloying