This chapter discusses the dislocation core effects on mobility. Its purpose is to discuss the atomic structure and interactions in the dislocation core and their effects on dislocation mobility from the standpoint of theoretical concepts, physical models and simulation studies, with due consideration of relevant experimental results. The major emphasis is placed on physical ideas and observations. In fact, technical details of modeling and experiments are only briefly mentioned and only where required for clarification of physics issues or for interpretation of results. The existence of glide and shuffle sets of dislocation positions in diamond cubic semiconductors introduces still more complexity with regard to the role of core mechanisms in dislocation motion. Plasticity behavior of BCC metals is controlled, to a large extent, by the motion of screw dislocations.
Fatigue is a dominant failure mechanism of several engineering components. One technique for increasing the fatigue life is by inducing surface residual stress to inhibit crack initiation. In this review, a microstructural study under various bulk (such as severe plastic deformation) and surface mechanical treatments is detailed. The effect of individual microstructural feature, residual stress, and strain hardening on mechanical properties and fatigue crack mechanisms are discussed in detail with a focus on nickel-based superalloys. Attention is given to the gradient microstructure and interface boundary behavior for the mechanical performance. It is recommended that hybrid processes, such as shot peening (SP) followed by deep cold rolling (DCR), could enhance fatigue life. The technical and scientific understanding of microstructural features delineated here could be useful for developing materials for fatigue performance.
We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero.