Mechanics of disclinated interfaces and cracks in polycrystalline an nanocrystalline materials

Abstract

Gain boundaries (GBs) and crystal lattices in nanocrystalline materials contain defects, which may grow and induce failure of the materials. A critical issue for developing nanocrystalline materials is thus the modeling of material microstructures and constituent defects as well as the simulation of their behavior under load. In particular, the disclination defect, commonly found in nanocrystalline materials, is investigated in this research. The research focuses on the description of material interfaces by a disclination dipole wall and on the investigation of cracks initiating from disclinations. First, the mechanics model of an interfacial wedge disclination dipole wall in a hexagonal bicrystal is established by the method of image dislocations. The exact closed-form solutions for the elastic stress and strain energy density are shown to be of the form of the logarithm of hyperbolic and trigonometric functions of complex parameters. The results show that the stress, strain energy density and strain energy all depend significantly on the orientational and material inhomogeneities. Second, the disclination-structural unit model in conjunction with the mechanics model of the dipole wall is developed for the physical description of GBs in hexagonal bicrystals. For [1100] symmetrical tilt GBs in cobalt and titanium, it is shown that the GB stress field and energy depend strongly on the misorientation. In particular, the GB stress field is more localized in high-angle boundaries than in small-angle boundaries and severe distortion of the stress field results from even a small inhomogeneity. The energy-misorientation curve is characterized by cusps associated with favored 1