Day: February 20, 2012

Mesoscale Anisotropic Deformation and Damage Nucleation In Polycrystalline Ti Alloy

Friday, February 24, 2012 3:00 pm – 4:00 pm
Room 610, M&M Building

M. A. Crimp
Chemical Engineering and Materials Science
Michigan State University, East Lansing, MI

Abstract

A combination of experimental characterization and crystal plasticity finite element modeling(CPFEM) has been used to study the anisotropic deformation of a number of titanium alloys.Studies have been carried out in the near surface region of 4-point bend specimens, where theglobal stress can be approximated as uniaxial tension.  Specific microstructural patches havebeen characterized prior to deformation using electron backscattered electron diffractionorientation imaging microscopy (OIM).  Specimens have been deformed both in-situ in scanningelectron microscopy (SEM) and ex-situ, facilitating a range of experimental characterizationmethods including optical microscopy, atomic force microscopy, SEM based backscatteredelectron imaging, OIM, and channeling contrast imaging, as well as 3-D X-ray diffraction.  Thesestudies have allowed a comprehensive experimental characterization of the nature of plasticdeformation and damage nucleation in the microstructural patches.  To complement thesestudies, quasi 3-D FEM meshes, developed based the experimentally characterizedmicrostructural patches, have been computationally deformed.  While the simulations accuratelyreproduce significant aspects of the experimental studies, including some crystal rotations andsurface topography development, further work to include grain boundary behavior in thesimulations is needed.

More information: Mesoscale Anisotropic Deformation and Damage Nucleation In Polycrystalline Ti Alloy


BaTiO3 Glass-Ceramics Composites For High Energy Storage Capacitors

Thursday, February 23 2012 2:00 p.m.
Room 610, M&M Building

Douglas B. Chrisey
Department of Material Science and Engineering, Department of Biomedical Engineering
Rensselaer Polytechnic Institute, Troy, NY, 12180

Abstract

Renewable energy sources require large-scale power storage so that their inherently intermittent supply of power can meet demand.  For capacitive energy to have the necessary high volumetric and gravimetric energy storage density this will require the dielectric layer to simultaneously possess a high dielectric constant and a high breakdown strength, e.g., in excess of 10,000 and 1 MV/cm, respectively.  To be a realistic solution for renewable energy storage, it must also be low cost and scalable, i.e., no roadblocks from the laboratory prototype to large scale production, and to achieve the all of the aforementioned requirements we have exploited a glass-ceramic phase.  It is expected that glass-ceramics composites will have higher breakdown strength than that of a sintered ceramic alone, because the glass would displace the air-filled voids.  Due to the dielectric mixing rule, the dielectric constant of the composite mixture will then be limited by the low permittivity of the glass phase in comparison to the ceramic phase.  In our work, we use a glass phase that can undergo a phase transformation into BaTiO3-precipitating glass-ceramic by controlled crystallization (annealing temperature).  The benefit of doing this is that we achieve a higher dielectric constant of composite mixture, due to the additional high dielectric constant BaTiO3 phase, while also improving the high breakdown strength. It was demonstrated that this BaTiO3-precipitaing glass-ceramic and BaTiO3 ceramic composite are promising for improved dielectric properties for high-density energy storage capacitors.