SUMMARY

The objective of this thesis is to elucidate the mechanisms of plasticity in nanoscale metals and alloys by atomistic modeling and simulation. We propose to study the nanoscale mechanisms of plastic deformation in elemental metals. Our work will focus on understanding how dislocations and twins nucleate in single crystals. The proposed research involves two thrusts: (I) Interatomic potential finite element method will be used to determine when, where and how dislocation will nucleate during nanoindentation in metals such as Cu, Al and Ni. We will explore the effects of indentation orientation on the characteristics of activated dislocation sources. (II) Reaction path modeling will allow us to study the competition between dislocation nucleation and twinning in nanopillars under different strain rates, temperatures and loading modes. Results will provide insight into the nanoscale mechanisms of plastic flow, and could provide guidance to nanomechanical experiments in the future. We also propose to study the mechanisms and size effects of martensite phase transformation in NiTi shape memory alloys. we integrate the interatomic potential, energy minimization and molecular dynamics simulation to study the twin structures and phase transitions. Our work will address the following questions: What are the atomic-level structural characteristics unique to the nanoscale twins in NiTi? How does the twin size affect the phase transformation? How do defects influence the deformation of NiTi? Results will not only generate new insights into the martensitic phase transformation in nanostructured NiTi, but also provide an effective modeling framework for studying the diffusionless phase transition in large systems with atomic resolution.