Publikationsserver der RWTH Aachen University
Atomistic simulations of grain boundary migration in face centred cubic metals
Abstract
dc:descriptionIn this work, atomistic grain boundary (GB) migration and GB self-diffusion simulations of planar [001] twist GBs as well as various planar tilt GBs in face-centred cubic bicrystals have been performed. The utilized simulation method of choice was molecular dynamics (MD). Due to the planar geometry of the studied GBs, no driving force (DF) on the GB is exerted due to GB curvature. Therefore one necessary and important feature of this work was to derive DF concepts to drive planar GBs continuously within atomistic simulations. Two novel DF concepts within atomistic simulations were presented and discussed in detail in this work, namely an elastic DF concept as well as the so-called orientation-correlated DF concept. Both DFs are bulk concepts and their physical nature as well their physical behaviour are quite comparable. Extensive simulations were performed on planar [001] low-angle as well as high-angle twist GBs utilizing the elastic and orientation-correlated DF. Utilizing these concepts planar [001] twist GBs could be driven continuously. As expected according to general rate theory of GB migration, the computed GB velocity depended linearly on the installed DF in the system. The DF itself was computed in-situ during the conducted MD simulations. The GB velocity was extracted from GB position versus time plots. Performing numerous simulations at different DF magnitudes as well as temperatures, the temperature dependence of GB mobility was successfully computed. The computed activation parameters following an Arrhenius description reflected two GB regimes, namely a low-angle and a high-angle regime. The activation enthalpies of the [001] high-angle GBs as well as observed configurations of the displacement fields of atoms in distinct (002) planes of these GBs during the process of re-orientation reveal that at least some of the studied [001] high-angle twist GBs move by a collective shuffle mechanism. The studied low-angle [001] twist GBs are characterized structually and related to GB migration properties like activation enthalpy and GB migration mechanism by their discrete screw dislocation network. Additionally it was shown in this work that GB migration and GB self-diffusion are distinct different processes. The physical properties of GB migration of [001] twist GBs either driven by an elastic DF or orientation-correlated DF are equivalent. Since hardly any experimental data exists on GB migration of twist GBs and since tilt GBs are considered to dominate materials behaviour, the simulation efforts were extended to study various tilt GBs. According to the successful results of GB migration of [001] twist GBs in the presence of an elastic DF, the elastic DF concept was applied to symmetrical tilt GBs. Although finite distance GB migration could be achieved with the elastic DF, no truely continuous GB migration was achieved. Investigating this behaviour, it was found that the initially installed elastic DF was eventually decreasing to zero due to conversion effects of strain tensor components. It could be shown that strain tensor components necessary to yield an elastic DF were converted during the course of the simulations from being elastic into plastic strain components. This behaviour is connected to the finding that these strain tensor components initiate GB sliding which leads to the build-up of plastic strain. According to these findings, the elastic DF concept can not be successfully applied to symmetrical as well as asymmetrical tilt GBs to drive them continuously. Finally utilizing the orientation-correlated DF on the SIGMA 5 (210) symmetrical as well as on two asymmetrical SIGMA 5 [001] tilt GBs demonstrates that any tilt GB can be driven by the orientation-correlated DF concept. This result is a major highlight and breakthrough of this work since it demonstrates the successful implementation of the orientation-correlated DF concept to drive any kind of planar GB continuously. Again major aspects related to GB migration as mentioned above for the [001] twist GBs were found for the studied SIGMA 5 GBs as well. For example again it is found that GB migration and GB self-diffusion are distinctly different processes.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2004
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Schönfelder, Bernd
- Contributors dc:contributor
-
- Gottstein, Günter
Subjects
dc:subject × 9Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- eng
Identifiers
dc:identifier.*- OAI identifier oai:identifier
- oai:publications.rwth-aachen.de:59591