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Grain-boundary Structure (grain-boundary + structure)
Selected AbstractsEffects of Grain-Boundary Structure on the Strength, Toughness, and Cyclic-Fatigue Properties of a Monolithic Silicon CarbideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2000Da Chen An in situ -toughened silicon carbide (ABC-SiC) has been examined in the as-processed condition, where the grain-boundary films are predominantly amorphous, and following thermal exposure at a temperature of 1300°C, where the films become fully crystalline. Previous work has shown that, at elevated temperatures (up to 1300°C), after the grain-boundary films crystallize in situ, only a marginal reduction in strength, fracture toughness, and cyclic-fatigue crack-growth properties is observed, in comparison with those of the as-processed microstructure at 25°C. In the present study, the effect of such crystallization on the subsequent strength, toughness, and fatigue properties at 25°C is examined. Little or no degradation is observed in the room-temperature properties with the crystallized grain-boundary films/phase; in fact, although the strength shows a small reduction (,3%), the fracture toughness and fatigue-crack-growth threshold both increase by ,20%, compared with that of the as-processed structure with amorphous grain-boundary films. [source] Multifunctional Composites of Ceramics and Single-Walled Carbon NanotubesADVANCED MATERIALS, Issue 17 2009Nitin P. Padture Abstract Polycrystalline ceramic/single-walled carbon nanotube (SWNT) composites possess unique grain boundaries, containing 1D tortuous SWNTs bundles that form 2D tangled embedded nets. This unprecedented grain-boundary structure allows tailoring of multifunctional ceramic/SWNTs composites with unique combinations of desirable mechanical (toughness, strength, creep) and transport (electrical, thermal) properties. A brief discussion and analysis of recent developments in these composites are presented. [source] Direct Observation of Multilayer Adsorption on Alumina Grain BoundariesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2007Shen J. Dillon Grain-boundary films 0.6 nm in size have been observed on the grain boundaries of neodymia (Nd2O3)-doped alumina (,-Al2O3) sintered at 1800°C. Direct observation by high-angle annular dark-field imaging in the aberration-corrected scanning transmission electron microscope shows that this type of grain-boundary structure is the result of multilayer adsorption. Neodymium cations adsorb onto the faces of each of the two grains that comprise the grain boundary by substituting for aluminum cations. The positions of these cations are slightly distorted relative to the perfect lattice, and a third atomic layer in the core of the grain-boundary resides between these two layers. The measurements also confirm that the thickness deduced from high-resolution transmission electron microscopy lattice images are accurate. [source] Ab Initio Calculations of Pristine and Doped Zirconia ,5 (310)/[001] Tilt Grain BoundariesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2002Zugang Mao The structure of the cubic-ZrO2 symmetrical tilt ,5 (310)/[001] grain boundary is examined using density functional theory within the local density and pseudopotential approximations. Several pristine stoichiometric grain-boundary structures are investigated and compared with Z-contrast scanning transmission electron microscopy and electron energy loss spectroscopy results. The lowest-energy grain-boundary structure is found to agree well with the experimental data. When Y3+ is substituted for Zr4+ at various sites in the lowest-energy grain-boundary structure, the calculations indicate that Y3+ segregation to the grain boundary is energetically preferred to bulk doping, in agreement with experimental results. [source] | ||||||||||