Coherent twin boundaries are defects in materials, widely described as perfect interfaces theoretically and experimentally, playing a significant role in a variety of materials. The ability of coherent twin boundaries in strengthening, maintaining the ductility, and retaining high electrical conductivity is well documented. The integration of advanced computational and experimental techniques in this research will lead to a fundamentally new understanding of plasticity and fracture in metallic metals containing these defects because of newly-developed imaging tools and computational models. The multidisciplinary research team will allow new understanding and may accelerate the deployment of the next-generation structural materials with tolerance to extreme environments such as high radiation exposure and high temperature. The education and outreach components of this project will also include research training and mentoring of undergraduate and graduate students, organization of an international symposium, and activities for attraction and retention of freshman and sophomore college students in STEM.
This combined computational and experimental study aims to understand the fundamental role of newly-observed kink-like twin boundary defects in the deformation and fracture of nanotwinned metals, with a particular focus on face-centered cubic metals with low and intermediate stacking-fault energies. The objectives of this project are three-fold. First, we will study new kink-dependent plastic deformation processes in model nanotwinned metals in Cu, Ag and Ag-Cu alloys using atomistic simulations tightly coupled to a new nanodiffraction mapping technique inside a transmission electron microscope, in-situ synchrotron x-ray diffraction tensile tests, and atomic force microscopy nanoindentation experiments. Second, we will examine the impact of temperature, stacking-fault energy, defect density, and grain boundary structure on hardening and softening mechanisms in these metals. Third, a multiscale approach using quasi-continuum computer simulations will be deployed to model the effects of twin boundary defects and twin size on fracture toughness. This project will benefit from the expertise of the PI in theoretical and computational materials research in nanotwinned systems, and from collaboration with scientists at Lawrence Livermore National Laboratory and Ames Laboratory who will perform state-of-the-art experiments on freestanding nanotwinned films.
