Function Of Grain Boundary Misorientation Research Articles

Effect of grain boundary misorientation on the apparent diffusivity in nanocrystalline aluminum by atomistic simulation study

To obtain a fundamental understanding of the effect of structure and geometry of grain boundary on the diffusion kinetics in nanocrystalline materials, the influence of grain boundary misorientation on the effective diffusion coefficient (apparent diffusivity) in nanocrystalline aluminum was investigated using molecular dynamics simulations. Nine series of [001] symmetric tilt grain boundaries, including high and low symmetric boundary planes, were studied. The apparent diffusivity in the samples was calculated in the temperature range from 423 K to 823 K by monitoring the mean square displacement of atoms as a function of simulation time. A temperature dependence of the effective diffusion coefficient according to the Arrhenius law was obtained for all samples. It is found that the apparent diffusivity is anisotropic and it is a strong function of grain boundary misorientation at low and high temperatures. At all temperatures, Σ29 [001]/(520) symmetric tilt grain boundary with misorientation angle of 43.68° exhibits the highest effective diffusion coefficient among the investigated grain boundaries. The simulation results show that the activation energy and pre-exponential factor are affected significantly by the grain boundary misorientation angle. Moreover, the results indicated that the misorientation dependence of activation energy for diffusion exhibits two local maxima, which correspond to two symmetric tilt grain boundaries. Additional calculation of misorientation dependence of the pre-exponential factor shows two local minima at the same symmetric tilt grain boundaries. The misorientation dependence of the effective diffusion coefficient was explained on the basis of grain boundary energy and the crystallographic structure of grain boundary.

An investigation into the influence of grain boundary misorientation on the tensile strength of SiC bicrystals

ABSTRACTIn this work, molecular dynamics (MD) and Car-Parrinello molecular dynamics (CPMD) simulation-based analyses are performed to understand the influence of grain boundary (GB) misorientation on the tensile strength of SiC bicrystals. The tensile strength is governed by the changes in electron density and bond strength of atoms in GBs. An investigation of dislocation activity during mechanical deformation shows that the extent of the propagation of dislocations across the bicrystal grains is directly proportional to the extent of GB misorientation. An analytical relation that predicts the tensile strength as a function of GB misorientation is developed.

Anisotropic Grain Boundary Segregation in Y-Doped TiO2

A variety of properties of polycrystalline TiO2, such as conductivity, creep and grain boundary diffusion, are strongly dependent on the atomic-level structure and chemistry of grain boundaries. TiO2 has been studied as a model dielectric system because of its relatively simple structure and well-understood point defect chemistry. Defect segregation in grain boundaries of polycrystalline and bi-crystal TiO2 have been studied by several groups and significant variations in solute segregation levels from boundary to boundary were observed. in this paper, we address this issue of anisotropic grain boundary segregation. We have measured solute segregation as a function of grain boundary misorientation to determine any correlation between segregation and misorientation.Yttria-doped TiO2 polycrystalline samples were prepared by mixing 99.999% pure TiO2 powder with 0.1% mole percent 99.99% purity Y(NO3)3 (both powders are commercially available from Aldrich Co. or Alfa Co.), followed by uni-axial pressed to 200-400Pa and sintering at 1300 °C for about 5-7 hours.