Atomistic Simulations of Deformation in Metallic Nanolayered Composites

• Main Author: Huang, Sixie
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2019
• Subjects: Engineering; Materials science
• ISBN: 9781085563215; 1085563219

The mechanical behavior of Metallic Nanolayered Composites (MNCs) is governed by their underlying microstructure. In this dissertation, the roles of the interlayer spacing (grain size, d) and the intralayer biphase spacing (layer thickness, h) on mechanical response of Cu/Nb MNCs are examined by Molecular Dynamics (MD) simulations.The study of the strength of MNCs show that small changes in both d and h play a profound role in the relative plastic contributions from grain boundary sliding and dislocation glide. The interplay of d and h leads to a very broad transition region from grain boundary sliding dominated flow, where the strength of the material is weak and insensitive to changes in h, to grain boundary dislocation emission and glide dominated flow, where the strength of the material is strong and sensitive to changes in h. The study of the fracture behavior of MNCs shows that cracks in Cu and Nb layers may exhibit different propagation paths and distances under the same external loading. Interfaces can improve the fracture resistance of the Nb layer in Cu/Nb MNCs by providing mobile dislocation sources to generate the plastic strain at the crack tip necessary for crack blunting. Increasing the layer thickness can further enhance the fracture resistance of both Cu and Nb layers, since the critical stress for activating dislocation motion decreases with increasing the layer thickness. A novel atomistic-informed interface-dislocation dynamics (I-DD) model has been developed to study Metal-Ceramic Nanolayered Composites (MCNCs) based on the key deformation process and microstructure features revealed by MD simulations. The I-DD predicted results match well with the prior experimental results where both yield stress and strain hardening rate increase as the layer thickness decreases. This I-DD model shows great potential in predicting and optimizing the mechanical properties of MNCs.