Committee Members:

Prof. David McDowell, Advisor, ME/MSE

Prof. Preet Singh, MSE

Prof. Josh Kacher, MSE

Prof. Min Zhou, ME/MSE

Xiaowang Zhou, Ph.D.,Sandia National Laboratories

Concurrent Atomistic-Continuum Studies of Interface/Dislocation Interactions in Nanolaminates and with He Bubbles in Stainless Steels

Abstract:

The interactions between dislocations and interfaces between materials with different structures, chemistry, and/or orientation primarily mediate the mechanical properties of polycrystalline materials. Studying these interactions necessitates the consideration of non-ideal interface structures which can arise through interdiffusion of constituent species, the presence of defects such as voids or He bubbles, and the build-up of dislocation content from previous interactions. Analysis of these interface structures requires atomic resolution to capture due to the complex dislocation reactions that are not known a priori. Computational cost precludes application of atomistic methods for interfaces that have large characteristic lengths or for studying the accumulation of dislocation content from sequential interactions, both of which require large spatial domains. Instead, we desire a multi-scale modeling approach which renders the interface at full atomistic resolution while considering the bulk of the model with a lower cost description. The Concurrent Atomistic-Continuum (CAC) method is a coarse-graining atomistics approach that utilizes full atomistic resolution at locations with high degrees of atomic restructuring to preserve predictive accuracy, while using a coarse-grained description elsewhere to reduce degrees of freedom. CAC utilizes a unified model form for both coarse-grained and atomistic regions that depends only on the interatomic potential; an integral formulation finite element approach in CAC enables use of a discontinuous mesh which can accommodate dislocations and does not require bridging methods to join coarse-grained and atomistic regions. CAC will be applied to the study of the deformation of nanolaminate materials with semi-coherent interfaces to understand interface evolution as a result of the glide of threading dislocations. The relation between interface misfit dislocation density and resistance of the interface to dislocation glide will specifically be compared. CAC will also be used to study the sequential interactions of dislocations with He bubbles embedded within 3 and 11 grain boundaries in stainless steels. The influence of grain boundary energy and structure on the obstacle strength of the He bubble/grain boundary dislocation reactions will provide insight into irradiation induced embrittlement. This work will characterize mechanisms of dislocation/interface interactions and will highlight the effects of evolving interface structure on the interaction mechanisms while demonstrating the necessity of multi-scale modeling schemes to accurately estimate evolution of dislocations and interface structure and properties.