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Small Grain Size (small + grain_size)
Selected AbstractsPlasticity and Grain Boundary Diffusion at Small Grain Sizes,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Gerhard Wilde Bulk nanostructured,or ultrafine-grained materials are often fabricated by severe plastic deformation to break down the grain size by dislocation accumulation. Underlying the often spectacular property enhancement that forms the basis for a wide range of potential applications is a modification of the volume fraction of the grain boundaries. Yet, along with the property enhancements, several important questions arise concerning the accommodation of external stresses if dislocation-based processes are not longer dominant at small grain sizes. One question concerns so-called "non-equilibrium" grain boundaries that have been postulated to form during severe deformation and that might be of importance not only for the property enhancement known already today, but also for spectacular applications in the context of, e.g., gas permeation or fast matter transport for self-repairing structures. This contribution addresses the underlying issues by combining quantitative microstructure analysis at high resolution with grain boundary diffusion measurements. [source] Enhanced Strength and Ductility of Ultrafine-Grained Ti Processed by Severe Plastic Deformation,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Irina Semenova This work deals with the study of strength and ductility in ultrafine-grained (UFG) Ti Grade 4 produced by equal channel angular pressing (ECAP) in combination with subsequent thermomechanical treatments. We found that additional annealing of UFG Ti resulted in unusual enhancement of strength and ductility, which is associated with not only small grain size but also with a grain boundary structure. The origin of this phenomenon is investigated using the results of transmission electron microscopy and atom probe tomography. The innovation potential of UFG Ti for medical use is considered. [source] Novel Structural Modulation in Ceramic Sensors Via Redox Processing in Gas BuffersINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2006Abdul-Majeed Azad High selectivity, enhanced sensitivity, short response time, and long shelf-life are some of the key features sought in the solid-state ceramic-based chemical sensors. As the sensing mechanism and catalytic activity are predominantly surface-dominated, benign surface features in terms of small grain size, large surface area, high aspect ratio and, open and connected porosity, are required to realize a successful material. In order to incorporate these morphological features, a technique based on rigorous thermodynamic consideration of the metal/metal oxide coexistence is described. By modulating the oxygen partial pressure across the equilibrium M/MO proximity line, formation and growth of new oxide surface on an atomic/submolecular level under conditions of "oxygen deprivation," with exotic morphological features, has been achieved in potential sensor materials. This paper describes the methodology and discusses the results obtained in the case of potential semiconducting ceramic oxide-based carbon monoxide and hydrogen sensors with enhanced characteristics. [source] Spark Plasma Sintering of an Infrared-Transparent Y2O3,MgO NanocompositeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2010DongTao Jiang A novel optically transparent ceramic nanocomposite Y2O3,MgO was produced using spark plasma sintering technique. Sintering parameters was optimized to obtain fully dense material while maintaining nanoscale grain size. The sintered nanocomposite has an excellent infrared transmission as a result of small grain size and homogeneous microstructure. Postsinter annealing can significantly improve the transmission. Overly larger grain size severely degrades the transmittance. [source] High-Temperature Oxidation Behavior of High-Purity ,-, ,-, and Mixed Silicon Nitride CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2002M. Backhaus-Ricoult High-temperature oxidation behavior, microstructural evolution, and oxidation kinetics of additive-free ,-, ,-, and mixed silicon nitride ceramics is investigated. The oxidation rate of the ceramics depends on the allotropic ratio; best oxidation resistance is achieved for ceramics rich in ,-phase. Variations in the oxidation kinetics are directly related to average grain size and glass distribution in the oxidation scale. The oxygen contents incorporated into the Si3N4 phase before its dissolution at the oxidation front affects the local glass composition and thereby yields nucleation and growth rates of SiO2 crystallites within the glass phase and a final oxidation scale microstructure, which depend on the incorporated oxygen contents. For the ,-polymorph, the dynamic oxygen solubility is found to remain negligible; therefore, a nitrogen-rich glass forms at the oxidation front, which promotes devitrification and yields a scale with small grain size and thin intergranular glass films. ,-Si3N4 is observed to form oxygen-rich solid solutions on oxidation, which are in contact with silicon oxynitride or oxygen-rich glass. Nucleation of cristobalite in the latter is sluggish, yielding coarse-grained oxidation scales with thick intergranular glass film. [source] Helicon-wave-excited plasma sputtering deposition of Ga-doped ZnO transparent conducting filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2006Mutsumi Sugiyama Abstract Sputtering deposition of Ga-doped ZnO (ZnO:Ga) thin films was carried out using the helicon-wave-excited plasma sputtering (HWPS) method. The films sputtered above 150 °C had a preferential {0001} orientation. According to the surface-damage-free nature, the films having featureless surface morphology exhibited an optical transmittance greater than 80% in the visible spectral wavelengths. However, because the deposition temperature was limited to 250 °C, the electron mobility was limited to as low as 2,3 cm2/V s due to the small grain size (,25 nm). The results indicate that ZnO:Ga films deposited by HWPS can be used in the transparent conducting oxide layer, provided that higher electron mobility is achieved. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Adduct formation of CP2Mg with NH3 in MOVPE growth of Mg-doped InNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007Y. Nagai Abstract The Mg doping for MOVPE InN has been studied using biscyclopentadienyllmagnesium CP2Mg as a Mg source. The InN samples grown near the upstream end of the 18 cm long susceptor have very small grain size and contain a high level of C and H contamination. The XPS analysis of the deposits obtained by the supply of CP2Mg together with NH3 reveals that new Mg compounds are formed near the upstream end of the susceptor. The new compounds are adducts of CP2Mg and NH3, because they can not be formed when only CP2Mg is supplied. The adduct formation seems to be a cause for the very small grain size and the high levels of C and H contamination. The adduct formation is suppressed at positions with a distance more than 9 cm from the upstream end. This means that designs of reactor and susceptor are very important for successful Mg doping of InN with CP2Mg. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Plasticity and Grain Boundary Diffusion at Small Grain Sizes,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Gerhard Wilde Bulk nanostructured,or ultrafine-grained materials are often fabricated by severe plastic deformation to break down the grain size by dislocation accumulation. Underlying the often spectacular property enhancement that forms the basis for a wide range of potential applications is a modification of the volume fraction of the grain boundaries. Yet, along with the property enhancements, several important questions arise concerning the accommodation of external stresses if dislocation-based processes are not longer dominant at small grain sizes. One question concerns so-called "non-equilibrium" grain boundaries that have been postulated to form during severe deformation and that might be of importance not only for the property enhancement known already today, but also for spectacular applications in the context of, e.g., gas permeation or fast matter transport for self-repairing structures. This contribution addresses the underlying issues by combining quantitative microstructure analysis at high resolution with grain boundary diffusion measurements. [source] Mechanisms and Mechanics Governing the Indentation of Polycrystalline AluminaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2008Zhensong Wei A constitutive model for the inelastic deformation of polycrystalline alumina that accounts for both microcrack growth and plastic slip is implemented into a commercial finite element code. To establish its applicability, the code is used to simulate the deformation that occurs upon spherical and conical indentation. Inelastic zones and indentation pressures are predicted over a range of grain size and compared with measurements. The model replicates the mechanism transition from plasticity control at small grain sizes to micro-crack-control at large grain sizes. It also predicts an extensive micro-crack-dominated inelastic zone at large grain size that reduces the indentation pressures. [source] | |||||||||||||