Grain boundary mobility tensor and topological phase transitions / Kongtao Chen.

Format:

Book

Thesis/Dissertation

Author/Creator:

Chen, Kongtao, author.

Contributor:

Srolovitz, David J., degree supervisor.

University of Pennsylvania. Department of Materials Science and Engineering, degree granting institution.

Language:

English

Subjects (All):

Physics.

Mechanics.

Materials science.

Materials science and engineering--Penn dissertations.

Penn dissertations--Materials science and engineering.

Local Subjects:

Physics.

Mechanics.

Materials science.

Materials science and engineering--Penn dissertations.

Penn dissertations--Materials science and engineering.

Genre:

Academic theses.

Physical Description:

1 online resource (130 pages)

Contained In:

Dissertations Abstracts International 82-07B.

Place of Publication:

[Philadelphia, Pennsylvania] : University of Pennsylvania ; Ann Arbor : ProQuest Dissertations & Theses, 2020.

Language Note:

English

System Details:

Mode of access: World Wide Web.

text file

Summary:

The grain boundary (GB) mobility relates the GB velocity to the driving force. While the GB velocity is normally associated with motion of the GB normal to the GB plane, there is often a tangential motion of one grain with respect to the other across a GB; i.e., the GB velocity is a vector. Grain boundary motion can be driven by a chemical potential that jumps across a GB or by shear applied parallel to the GB plane; the driving force has three components. Hence, the GB mobility must be a tensor (the off-diagonal components indicate shear coupling). Recent molecular dynamics (MD) and experimental studies show that the GB mobility may abruptly jump, smoothly increase, decrease, remain constant or show multiple peaks with increasing temperature. Performing MD simulations on symmetric tilt GBs in copper, we demonstrate that all six components of the GB mobility tensor are non-zero (the mobility tensor is symmetric, as required by Onsager). We demonstrate that some of these mobility components increase with temperature while, surprisingly, others decrease. We develop a disconnection dynamics-based statistical model that suggests that GB mobilities follow an Arrhenius relation with respect to temperature T below a critical temperature Tc and decrease as 1/T above it. Tc is related to the operative disconnection modes and their energetics. We implement this model in a kinetic Monte Carlo (kMC); the results capture all of these observed temperature dependencies and are shown to be in quantitative agreement with each other and direct MD simulations of GB migration for a set of specific GBs. We demonstrate that the abrupt change in GB mobility results from a Kosterlitz-Thouless (KT) topological phase transition. This phase transition corresponds to the screening of the long-range interactions between (and unbinding of) disconnections. This phase transition also leads to abrupt change in GB sliding and roughening. We analyze this KT transition through mean-field theory, renormalization group methods, and kMC simulation. Finally, we examine the impact of the generalization of the mobility and KT transition for grain growth and superplasticity.

Notes:

Source: Dissertations Abstracts International, Volume: 82-07, Section: B.

Advisors: Srolovitz, David J.; Committee members: Andrea Liu; Prashant Purohit; Vivek Shenoy.

Department: Materials Science and Engineering.

Ph.D. University of Pennsylvania 2020.

Local Notes:

School code: 0175

ISBN:

9798557048439

Access Restriction:

Restricted for use by site license.

This item must not be sold to any third party vendors.