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Theory and modeling of the mechanical behavior of nanoscale and finescale multilayer thin films

Li, Qizhen
http://rave.ohiolink.edu/etdc/view?acc_num=osu1095684024

Abstract Details

2004, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.
In this work, a 3D Dislocation Cellular Automaton (CA) model is developed and calibrated first; then the model is applied to study the mechanical properties of nanoscale and finescale multilayer thin films. In the 3D dislocation model, the study object has a FCC structure. The structure is divided into cubic cells with edges along crystallographic <100> directions. Crystallographic {111} slip planes with three-fold symmetry are discretized into equilateral triangular patches with sides along <110> directions. Dislocation lines are represented by a set of triangular sides within {111} planes. These triangular patches slip provided there is a sufficient driving force associated with reduction in system energy. Perfect <110>/{111} dislocations are considered. The resulting variables are the triangular patch size and dislocation core cut-off, measured relative to Burgers vector magnitude b. To calibrate this model, three examples involving operation of a Frank-Read source are chosen. These examples also highlight the benefits and drawbacks of the method. A benefit to discretization is that dislocation evolution may be analyzed via spatial averaging over collections of patches, so that the discrete versus continuum nature of the results may be studied. Further, dislocation reactions and cross slip are accommodated easily and, in principle, Monte-Carlo schemes can be integrated into the evolution formalism. Overall, the discrete nature of the method is attractive for incorporating the kinetics of thermally activated states and for simplifying the range of geometries and threshold criteria associated with dislocation reactions. This 3D Dislocation Cellular Automaton model is employed to simulate yield and hardening in nanostructured metallic multilayer thin films. Threading and interfacial dislocation sources are studied. The films are composed of 2 types of alternating single crystalline FCC layers with a (001) epitaxy, a mismatch in stress-free lattice parameter, but no elastic modulus mismatch. Interfaces are assigned no additional strength except that from lattice parameter mismatch and interfacial dislocation arrays. Three regimes of tensile plastic response are identified based on the evolution of interfaces during tensile deformation. For smaller individual layer thickness, interfaces are coherent initially and remain so up to bulk yield (Regime I). For intermediate layer thickness, interfaces are coherent initially but become semi-coherent prior to bulk yield (Regime IIa). For larger layer thickness, interfaces are semi-coherent initially and acquire additional dislocation content prior to bulk yield (Regime IIb). The evolution of interfacial structure during deformation in Regimes IIa and IIb occurs due to deposition of dislocation content along interfaces by confined layer slip (CLS). The overall outcome is that the plastic strength of multilayer thin films increases with decreasing layer thickness until Regime I is encountered. Strength in Regime I may increase, reach a plateau, or even decrease. The results are consistent with experimental measurements of hardness, including the Ag/Al system in particular.
Peter Anderson (Advisor)
190 p.
Dislocation; Misfit; slip; MULTILAYER; Misfit Dislocation

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Citations

  • Li, Q. (2004). Theory and modeling of the mechanical behavior of nanoscale and finescale multilayer thin films [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1095684024

    APA Style (7th edition)

  • Li, Qizhen. Theory and modeling of the mechanical behavior of nanoscale and finescale multilayer thin films. 2004. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1095684024.

    MLA Style (8th edition)

  • Li, Qizhen. "Theory and modeling of the mechanical behavior of nanoscale and finescale multilayer thin films." Doctoral dissertation, Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1095684024

    Chicago Manual of Style (17th edition)

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© 2004, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.