Woodruff School of Mechanical Engineering
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Damage Nucleation at Grain Boundaries in Commercial Purity Titanium
Dr. Thomas Bieler
Department of Chemical Engineering and Materials Science, Michigan State University
Tuesday, January 19, 2010 at 7:45:00 PM
IPST Building, Ground Floor Seminar Room Building
Heterogeneous deformation near grain boundaries in polycrystalline α-titanium were investigated using a combination of experimental characterization and Crystal Plasticity FEM (CPFEM) simulation. Samples were deformed incrementally by four-point bending until microcracks were observed in grains or at grain boundaries. Active deformation systems were then identified using orientation-imaging microscopy (OIM), differential image correlation (DIC), electron channeling contrast imaging (ECCI), 3-D x-ray diffraction, and atomic force microscopy (AFM) to obtain accurate z-displacements across deformation twins and dislocation slip bands. The deformation system activity in a patch of grains was quantitatively assessed based on these data, and compared with calculations based on a global Schmid factor hypothesis. Local strains measured by this analysis were compared with CPFEM simulation results. CPFEM simulation showed that dislocation slip in soft oriented grains at the early stage would alter the local stress state near grain boundaries significantly, affecting the deformation processes in the volumes close to the grain boundaries. The computational model's sensitivity to grain boundary inclination beneath the sample surface was examined using information gained from 3D x-ray diffraction. This research was supported by NSF grant DMR-0710570 and DFG grant EL 681/2-1.
Dr. Bieler earned a B.A. in Applied Mechanics from UC San Diego ('78), a M.S. in Ceramic Engineering from University of Washington (Seattle, '80), worked for 5 years at Sandia National Labs in Livermore, CA in the Applied Mechanics Department, and then earned his Ph.D. at UC Davis in Materials Science ('89). Since then he has been at Michigan State University in East Lansing MI. Bieler's research interests have been in aluminum and titanium alloys, lead-free solder, and high purity niobium for superconductivity applications. Bieler has made extensive use of x-ray and electron back scattered diffraction methods to characterize microstructure, texture, thermal and mechanical history effects, deformation, and damage nucleation mechanisms.