Dislocations are line defects in crystalline materials and act as microscopic carriers of plastic deformation. Dislocation climb is the motion out of the slip plane with the assistance of vacancy or interstitial diffusions and plays important roles in plastic deformation at high temperature. How to properly determine climb velocity is a challenging task in dislocation dynamics simulations. This thesis focuses on modeling and simulations of dislocation climb, with emphasis on the non-local effect of vacancy/interstitial diffusions. Contributions are made in both methods development and applications to low angle tilt grain boundary properties, i.e., stability and point defect sink efficiency.

In the first part of the thesis, we derive a Green's function formulation for the clim...[ Read more ]

Dislocations are line defects in crystalline materials and act as microscopic carriers of plastic deformation. Dislocation climb is the motion out of the slip plane with the assistance of vacancy or interstitial diffusions and plays important roles in plastic deformation at high temperature. How to properly determine climb velocity is a challenging task in dislocation dynamics simulations. This thesis focuses on modeling and simulations of dislocation climb, with emphasis on the non-local effect of vacancy/interstitial diffusions. Contributions are made in both methods development and applications to low angle tilt grain boundary properties, i.e., stability and point defect sink efficiency.

In the first part of the thesis, we derive a Green's function formulation for the climb of curved dislocations and multiple dislocations. The dislocation climb velocity is determined from the Peach-Koehler force on dislocations through vacancy diffusion in a non-local manner. Analytical and numerical examples show that the widely used local mobility formula, which is based on straight infinite dislocations, is not generally applicable, except for a small set of special cases. We also present a numerical discretization method of this Green's function formulation appropriate for implementation in discrete dislocation dynamics simulations.

In the second part of the thesis, we systematically investigate the relaxation of slightly perturbed low angle tilt grain boundaries by climb of the constituent dislocations, including the contribution of the long-range interaction of dislocations through vacancy/interstitial diffusion to dislocation climb. The relaxation behavior of low angle grain boundaries due to dislocation climb is shown to be essentially different from that due to dislocation glide.

In the third part of the thesis, point defect sink efficiency of low angle tilt grain boundaries due to constituent dislocation climb are investigated through Green's function method in both non-irradiation and irradiation problems. Our calculations show that the low angle tilt grain boundary sink efficiency is determined by grain boundary structures, material properties and/or the irradiation conditions. We also derive an equivalent Robin boundary condition to incorporate the grain boundary dislocation climb effects for efficient simulations on the continuum level. These results gain a deeper understanding of grain boundary radiation damage scenario for designing radiation-tolerant materials.

The developed Green's function formulation and numerical algorithm for dislocation climb in discrete dislocation dynamics will provide tools for accurate and efficient simulations and deeper understandings of the related mechanical and plastic properties of crystalline materials.