| Dislocation-obstacle interactions play a significant role in determining the mechanical response of a material. Because higher stresses are needed for dislocations to bypass obstacles, these interactions reduce dislocation mobility and increase the yield strength of a material, as well as improve the work-hardening rate and the resistance to coarsening. The phenomenon of dislocation-obstacle interactions can be advantageous, as in the case of particle-strengthening to increase the creep strength of a material, or disadvantageous, as in embrittlement of a metal due to radiation-induced defects.; In order to accelerate the time from development to implementation of a new material, optimize production parameters, and accurately predict the behavior of a material while in service, it is necessary to develop robust material models based on fundamental physical inputs. Through careful experimentation, the nature of dislocation-obstacle interactions can be assessed, allowing key physical parameters to be identified and clarified. These can serve as the basis for developing new and accurate material models.; This thesis examines two types of dislocation-obstacle interactions: dislocation-particle interactions during creep deformation, and dislocation-loop interactions during deformation at room temperature. Dislocation-particle interaction studies in Al-Zn-Mg-Cu-Zr, Al-4Mg-0.3Sc, and Al-0.3Sc showed that temperature, coherency, and particle size play a role in determining the dominant bypass mechanism, and that interactions are more complex than what is considered in current models. A new mechanism for elevated temperature bypass of particles during creep deformation was revealed, in which dislocations interact directly with the particle-matrix interface, altering the interfacial structure, and affecting subsequent dislocation interactions. These results are discussed in relation to macroscopic behavior in steady-state creep experiments. In addition, dislocation-loop interaction studies show interactions to be of two types: intersection and elastic interactions. In-situ observations show annihilation, rotation, and repulsion of loops due to dislocation interactions. Comparison with current molecular dynamics simulations highlights the need to better understand these interactions in order to improve models for irradiated materials. |
