Grain Boundary Design using Ceramic Multiple Crystals and Plasticity

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In this year, alumina and zirconia multiple crystals were systematically fabricated, and the respective grain boundary structure and chemistry were characterized by high-resolution electron microscopy (HREM), energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS).Alumina multiple crystals were fabricated by a hot joining technique at 1500 ℃ in air to obtain ten kinds of tilt grain boundaries which included small angle, CSL and high angle grain boundaries. It was found that grain boundary energy strongly depended on the grain boundary characters, e.g., there were large energy cusps at low Σ CSL grain boundaries. But, main part of grain boundary energy is likely to be due to the strain energy around the grain boundary, and the contribution of atomic configuration is not so large. Small angle grain boundaries were consisted of an array of partial dislocation with Burgers vector of 1/3[1 1^^- 00] to form the stacking faults between the dislocations. The beh … More avior of grain boundary sliding was also investigated for typical grain boundaries by high-temperature creep test at 1400 ℃. As the result, the occurrence of grain boundary sliding was found to depend on the grain boundary geometry and atomic structure.Zirconia multiple crystals were also fabricated by a hot joining technique at 1600 ℃ in air to obtain ten kinds of tilt grain boundaries. It was found that the grain boundary structure and energy strongly depended on the grain boundary characters. For example, Σ9 grain boundary showed particularly high energy because the structure unit is highly strained at the boundary, although the amount of segregated yttrium is very large. In the case of Σ3 boundary, the atomic structure depends on the boundary planes. When boundary plane is (111), the boundary is perfectly straight along the (111) plane, however, facet structure is formed along (111)//(115) planes when the initial boundary plane is set parallel to (112). The relationship between grain boundary characters and energy will be discussed in detail from the view point of atomic structures and segregation for all kinds of grain boundaries in zirconia. Less