Abstract
The mobility of atoms in dislocation core regions is many orders of magnitude faster than in the surrounding lattice. This rapid atomic transport along dislocation cores plays a significant role in the kinetics of many material processes, including low-temperature creep and post-irradiation annealing. In the present work, a finite element based analysis of the dislocation core diffusion process is presented; based on a variational principle for the evolution of microstructure. A dislocation self-climb model is then developed by incorporating this finite element core diffusion formulation within the nodal based three-dimensional discrete dislocation dynamics framework. The behaviour of an isolated loop in bcc iron is briefly reviewed, and simulations are extended to include the loop coarsening processes of both parallel and non-parallel loops by self-climb plus glide mechanisms, in which the huge time scale separation between climb and glide is bridged by an adaptive time stepping scheme. Excellent agreement is obtained between the numerical simulation, the theoretical solution of rigid prismatic loops and published experimental results. The coarsening process of a population of loops is simulated to investigate the mechanisms of the accumulative interactions and large-scale-patterning in bcc materials.
Highlights
Dislocations are the predominant carriers of plastic deformation in crystalline materials (Anderson et al, 2017), which bridge the atomistic-scale deformation events with the macroscopic strength and plastic properties of crystalline materials
It is generally believed that dislocation glide motion, which follows the phonon-drag law (Cai and Bulatov, 2004), dominates at low temperature
The general thermodynamic variational principle is employed in the present work to derive the governing equations for dislocation core diffusion
Summary
Dislocations are the predominant carriers of plastic deformation in crystalline materials (Anderson et al, 2017), which bridge the atomistic-scale deformation events with the macroscopic strength and plastic properties of crystalline materials. The way in which point defects interact with the dislocation structures significantly affects the plastic behaviour of crystalline materials. It is, necessary to understand, and be able to model, these processes in an appropriate framework to predict the influence of climb on mechanical properties. The point defects are transported either along the dislocation line, in the core region, known as core (or pipe) diffusion; leading to a conservative climb motion called selfclimb (Anderson et al, 2017). The activation energy for core diffusion Ucore is approximately 0.6Ul (Frost and Ashby, 1982) and strongly depends on the dislocation character (Balluffi, 1970; Pun and Mishin, 2009) in FCC metals.
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