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Atomistic simulations of dynamic interaction between grain boundaries and solute clusters

University of British Columbia

Microstructure evolution during material processing is determined by a number of factors, such as the kinetics of grain boundary migration in the presence of impurities, which can take form of solid solution, second-phase precipitates or clusters. The dynamic interaction between grain boundaries and clusters has not been explored. In this work, a variety of simulation tools are utilized to approach this problem from an atomistic perspective. Atomistic simulations are first implemented to explore the parameter space of the solute drag problem, i.e. grain boundary migration in a binary ideal solid solution system, via a kinetic Monte Carlo framework. Depending on their diffusivity, solute atoms are capable of modifying the structure of a migrating boundary, leading to a diffusion-dependent drag pressure. A phenomenological model adapted from the Cahn model is proposed to explain the simulation results. The interaction between clusters and a migrating grain boundary is studied next using molecular dynamics simulations. The iron helium (Fe-He) system is chosen as the object of the study. A preliminary step towards such a study is to investigate the grain boundary migration in pure bcc Fe. An emphasis is placed upon demonstrating the correlation between the migration of curved and planar boundaries. Evidence that verifies such a correlation is established, based on the analyses on the shapes, the kinetics and the migration mechanism of both types of boundaries. Next, the formation of He clusters in the bulk and grain boundaries of Fe is examined. The cluster formation at the boundary occurs at a lower rate relative to that in the bulk. This is attributed to the boundary being a slow diffusion channel for interstitial He atoms. The overall effect of clusters on the boundary migration is twofold. Clusters reduce the boundary mobility via segregation; the magnitude of their effect can be rationalized using the Cahn model in the zero velocity limit. Clusters also act as pinning sources, delaying or even completely halting the boundary migration. A phenomenological model adapted from the Zener pinning model is used to discuss the role of clusters on grain boundary migration.

Text

2015-12-02

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/55662

Materials Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/