Aug. 13, 2019
- Associate Professor Nathan Mara and his collaborator, Professor Irene Beyerlein at UC Santa Barbara, have been awarded a grant of nearly $1 million from the Department of Energy, Basic Energy Sciences to control atomic-level interface structure in metal-based, layered nanocomposites to enhance mechanical properties such as strength, deformability, and toughness. This collaborative work will converge synthesis, measurement, and modeling efforts to elucidate basic, controllable structural variables of the 3D interface that affect structural material performance. It further leverages the experimental support of DOE-BES user facilities at Los Alamos National Laboratory, Sandia National Laboratories, and Oak Ridge National Laboratory.
To date, heterophase interfaces, as those found in multiphase composites, are generally regarded as two dimensional (2D), and chemically and structurally abrupt. Yet for decades, studies have pointed to the enormous influence that the properties of the interface in the out-of-plane dimension can have on strength and mechanical behavior.
In this work, the team aims to understand defect-interface interactions by pioneering basic research on 3D interfaces. 3D interfaces are heterophase interfaces that extend out of plane into the two crystals on either side and are chemically, crystallographically, and/or topologically divergent, in up to three dimensions, from both crystals they join. Such interfaces influence not only the unit processes of single dislocations that can be understood at the atomic scale, but also mechanical behavior at the scales of a few to tens of dislocations and the resulting bulk behavior. Very rarely are interfaces found in nature perfectly 2D over distances more than a nanometer or two. The goal of this program is to systematically develop an understanding on how 3D interfaces can affect mechanical response. The types of 3D interfaces studied will encompass those containing chemical gradients and/or boundary curvature (of relevance to particle-strengthened materials, irradiated materials, lamellar composites, and more).
For 3D interface effects, the scientific issues that need to be addressed concern attaining a multiscale understanding of defect physics from the unit process encompassing the alterations in the dislocation core as it reacts with an interface to the collective process of impinging dislocation arrays that transform the interface structure to collective processes of multiple slip interactions. Each process is expected to be profoundly altered by varying the chemical composition and structure of the 3D interface.The materials containing interfaces will be synthesized via physical vapor deposition, a process by which the composition and/or structure may be systematically varied in the out-of-plane direction. Microstructural characterization will consist of a suite of techniques that addresses structure at the atomic level (TEM, Atom Probe), as well as mesoscales (X-ray, neutron reflectometry). Mechanical behavior will be investigated at length scales ranging from atomic-level dislocation-interface interactions (in-situ TEM) to micro scales (in-situ SEM and ex-situ nanomechanical testing). A combination of atomic-scale simulation and mesoscale phase field modeling will be employed to simulate dislocation interactions with the 3D interfaces we synthesize. The calculations together will aim to uncover fundamental mechanistic details underlying the dislocation reactions, to extract the energies and critical stresses associated with them, and to relate them to the morphology and chemistry of the 3D interfaces.