Papers by Keyword: Nano-Crystalline Materials

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Authors: Reza Jafari Nedoushan, Mahmoud Farzin
Abstract: One of the Remarkable Differences between Mechanical Behavior of Nano-Crystalline and Coarse-Grained Materials Is Tension Compression Asymmetry that Has Been Experienced in Nano-Crystalline Materials. In this Paper a Constitutive Model Is Proposed which Considers Dominant Operative Deformation Mechanisms of Nano-Crystalline Materials Including Grain Interior Plasticity, Grain Boundary Diffusion and Grain Boundary Sliding. A Grain Size Dependent Taylor Type Polycrystalline Model Is Used to Predict Grain Interior Deformation. Three Dimensional Relationships Are Proposed to Relate Macro Stress and Strain Rate in Grain Boundary Mechanisms. The Effect of Normal Stress Acting on a Boundary Is Also Considered in Grain Boundary Sliding, Therefore, Effect of Hydrostatic Pressure Is Included in the Model. The Proposed Model Is Used to Predict Strength of Nano-Crystalline Copper in both Tension and Compression and Good Results Are Obtained Comparing with Experimental Data. The Model Also Predicts Various Behaviors of Nano-Crystalline Materials Observed in Literature's Experiments and Molecular Dynamic Simulations. Some Examples Are: Inverse Hall-Petch Effect; Tension and Compression Maximum Strength Grain Sizes; Tension Compression Asymmetry and its Change Vs. Grain Size and Strain Rate and the Yield Locus Shape.
Authors: Marcelo José Bondioli, Juliana K.M.Faria Daguano, A.A. Palmeira, Claudinei dos Santos, Kurt Strecker
Abstract: Zirconia is a bioceramic material widely used for dental implants. In this work, the sinterability of nano-crystalline powders has been investigated by dilatometry in the temperature range of 1250 to 1400 0C with isothermal holding times of up to 8h. A slight increase in grain growth and an increasing linear shrinkage have been observed with increasing sintering temperatures. The sintered samples were submitted to Vickers' hardness and KIC tests and the results compared regarding the sintering conditions. It has been verified that satisfactory hardness and fractures toughness have been achieved after sintering above 1300 0C during 8h.
Authors: Ying Deng, Xiang Xiong, Yan Hua Zhang, Ling Ling Peng
Abstract: High-energy ball mill of a mixture of H2C2O4·2H2O, Co (NO3)2·6H2O(A.R) has been used to produce nanocrystalline cobalt oxalate powders of nearly spherical shape. After the CoH2C2O4·2H2O powders have been dispersed by spray-drying, it has been decomposed at 400~550°C to obtain cobalt powders. The microstructure of the powders produced using ball milling and thermodynamical analysis for reaction and decomposition temperature have been studied. The powders were characterized by X-ray Diffraction, Scanning Electron Microscopy. It has been identified that a spherical, fcc structure, 100nm β-Co powders was synthesized.
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