Atomic-Scale Observation of Deformation in Nanoscale Body Center Cubic (BCC) Crystals

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

The metals used in mechanical components for small-scale devices at room temperature are normally of face center cubic character. Their mechanical behavior is generally well-known. However, at high temperature, these FCC metals become soft. Therefore, they are not suitable for high temperature application. In that case, body center cubic (BCC) nanostructured metals offer an alternative. These metals possess potentially desired high temperature strength. They are expected to serve in components in future high temperature device such as micro/nano electro-mechanical systems (MEMS/NMMS). Although the mechanical behavior of large-sized BCC metals is well-known, these macroscale properties cannot be directly used for nanometer-sized structures due to size effects. For the analysis of the small devices, it is necessary to know the mechanical behavior of BCC metals at small scales. However, there is lack of experimental data for the deformation process at small scales, and also there is no understanding of the deformation behavior of BCC metals at the nanometer scale. An in-situ mechanical testing approach inside a special high resolution transmission electron microscope (HRTEM) will be used in this research. This constitutes a new approach for studying the mechanical behavior at atomistic scale for nanometer-sized BCC metal specimens. The understanding of the mechanical behavior of nanometer-sized BCC crystals gained from this research will have direct impact on the design and fabrication of the high temperature MEMS/NEMS. The research on the in-situ HRTEM is expected to open a new approach to directly observe atomic-scaled deformation under mechanical stress. The results from the research are expected to contribute to the advancement of experimental mechanics and nanomaterials. The research will employ an in-situ tensile technique utilizing the most advanced instrument of high resolution transmission electron microscope (HRTEM) to reveal the deformation process in nanometer-sized BCC metal specimens. Firstly, nanometer-sized high strength BCC metal specimens will be fabricated in-situ. Secondly, tensile/compression experiment in-situ in the HRTEM will be conducted on these BCC specimens to documents deformation behavior at room temperature and high temperatures; Thirdly, lattice disturbance, dislocation dipole nucleation and competition between slip and twinning in the deformation process will be observed. Molecular dynamics modeling on key issues with a) dislocation dipole formation; b) nucleation of twinning and dislocation and c) competition of twinning and slip as function of crystal orientation will be carried out. The experiments will be carried out via national user facilities at the Environmental Molecular Sciences Laboratory (EMSL), Pacific Northwest National Laboratory, Richland, WA. This collaboration will build national research infrastructure.