In Chapter 9, we have seen that dislocations produce stress fields in the crystal that contains them. We have also seen that stresses produce Peach–Koehler forces on dislocations. Therefore, dislocations exert forces on each other through the stress fields they produce. In this chapter, we discuss dislocation–dislocation interactions, as well as the interaction between dislocations and other defects in the crystal, and the consequence of these interactions on the strength of bulk crystalline materials. We also consider the applications of these interactions to the mechanical properties of thin films.
In Section 10.1, we consider the interaction between two dislocations in an infinite medium, starting with two infinitely long parallel screw or edge dislocations. A few examples of the interaction between two non-parallel dislocation lines are also considered. In Section 10.2, we consider arrays formed by more than two dislocations of the same sign. When the dislocation interactions are attractive, the dislocation array corresponds to low angle grain boundaries. When the dislocation interactions are repulsive, the dislocation array is called a pile-up, because it can be found in front of an obstacle which blocks the dislocation motion.
In Section 10.3, we discuss two dislocation mechanisms which increase the strength of crystals. In the Taylor hardening mechanism, the strength is controlled by the interaction between dislocations themselves. In the Orowan bowing mechanism, the strength is associated with the presence of non-shearable particles, between which the gliding dislocation must bow for plastic deformation to occur. In Section 10.4, we consider several models in which the kinetics of dislocation motion, multiplication, and annihilation are used to explain the plastic deformation behavior of single crystals, such as the phenomena of yield point drop and sigmoidal creep.
The last two sections of this chapter deal with dislocations near interfaces. In Section 10.5, we discuss the conditions under which it becomes energetically favorable for dislocations to form at the interface between two materials to relieve the misfit strain. In Section 10.6, we discuss the stress and strain fields of dislocations near free surfaces and interfaces between twomaterials, and the forces exerted on these dislocations by the interfaces. For straight screw dislocations parallel to the interfaces, the effect of the interfaces can be modeled by sets of image dislocations in infinite, homogeneous elastic media.