Showing papers on "Grain growth published in 2003"
TL;DR: In this paper, the authors review the present understanding of film growth processes and their role in microstructural evolution as a function of deposition variables including temperature, the presence of reactive species, and the use of low-energy ion irradiation during growth.
Abstract: Atomic-scale control and manipulation of the microstructure of polycrystalline thin films during kinetically limited low-temperature deposition, crucial for a broad range of industrial applications, has been a leading goal of materials science during the past decades. Here, we review the present understanding of film growth processes—nucleation, coalescence, competitive grain growth, and recrystallization—and their role in microstructural evolution as a function of deposition variables including temperature, the presence of reactive species, and the use of low-energy ion irradiation during growth.
1,499 citations
02 Jan 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the authors investigated the dynamic recrystallization (DRX) characteristics of a Mg/3Al/1Zn (AZ31) alloy sheet at temperatures ranging from 200� /450 8C and constant strain rates of 1/10 4 � /2/104 s 1.
Abstract: Dynamic recrystallization (DRX) characteristics of a Mg/3Al/1Zn (AZ31) alloy sheet were investigated at temperatures ranging from 200� /450 8C and constant strain rates of 1/10 4 � /2/10 4 s 1 . The average grain size of the as-received alloy was 12 mm and can be refined to 6 mm via deformation at 250 8C, 1/10 4 s 1 to a strain level of 60%. Grain refinement was less effectiv ea t higher temperatures due to rapid grain growth. The grain refinement was attributed to dynamic continuous recrystallization which involves progressive increase in grain boundary misorientation and conversion of low angle boundaries into high angle boundaries. During DRX, subgrains were developed through the conversion of dislocation cell walls into subgrain boundaries. The presence of precipitates was not essential for dynamic recrystallization in the magnesium alloy being investigated because of its limited slip systems, low stacking fault energy and high grain boundary diffusion rate. # 2003 Elsevier Science B.V. All rights reserved.
395 citations
TL;DR: In this article, path coefficient analysis was conducted to study grain yield formation under different temperature and moisture regimes across Spain. But it was found that the number of kernels per spike had a significant contribution to grain yield, especially under drought stress conditions.
Abstract: Grain yield of durum wheat (Triticum turgidum L. var. durum) under Mediterranean conditions is frequently limited by both high temperature and drought during grain growth. Path coefficient analyses, based on an ontogenetic diagram, were conducted to study grain yield formation under different temperature and moisture regimes across Spain. Six ICARDA-CIMMYT inbred lines and four Spanish commercial cultivars were grown during 1998 and 1999 at two temperature regimes (cool and warm) and under both rainfed and irrigated conditions. Path coefficient analysis revealed that grain yield under cooler conditions was mostly determined by kernel weight, whereas the number of spikes per square meter predominantly influenced grain production in the warmer environments. The number of kernels per spike had a significant contribution to grain yield, especially under drought stress conditions. These associations do not clearly appear in the simple correlation analysis. Compensatory effects among yield components were almost absent in the cooler environments, probably due to the relative availability of water and N during the critical phases of plant development. Contrarily, under warmer conditions, negative effects of the number of spikes per square meter were registered on both the number of kernels per spike and kernel weight. Path analysis appears to be a useful tool for understanding grain yield formation and provides valuable additional information for improving grain yield via selection for its yield components.
375 citations
TL;DR: In this article, a new kinetic model based on oriented attachment-based growth was proposed to explain the asymptotic growth in the first stage of coarsening of mercaptoethanol-capped nanocrystalline ZnS.
Abstract: Crystal growth during hydrothermal coarsening of mercaptoethanol-capped nanocrystalline ZnS occurs via a two-stage process. In the first stage, the primary particle quickly doubles in volume. The initial growth rate can be fitted by an asymptotic curve that cannot be explained by any existing power-law dependence kinetic model developed for more coarsely crystalline material. High-resolution transmission electron microscope (HRTEM) data indicate that crystal growth within spherical nanoparticle aggregates occurs via crystallographically specific oriented attachment, despite the presence of surface-bound organic ligands. The size stabilizes for a period of time that depends on the coarsening temperature. In the second stage, following the dispersal of nanoparticles, an abrupt transition from asymptotic to cubic parabola growth kinetics occurs. The crystal growth data can be fitted by a standard Ostwald ripening volume diffusion model consistent with growth controlled by the volume diffusion of ions in solution. However, HRTEM data indicate that oriented attachment-based growth occurs in the early part of the second stage, followed by a significant reduction in aggregate surface topography, probably via surface diffusion as well as volume diffusion. We propose a new kinetic model based on oriented attachment-based growth to explain the asymptotic growth in the first stage of coarsening. The presence of surface-bound organic ligands may control the aggregation state of the nanoparticles and may permit an almost exclusive crystallographically specific oriented attachment-based growth to dominate in the first stage.
358 citations
TL;DR: In this paper, the effects of the timing and severity of drought, and increased temperature, on grain development of Hereward winter wheat were examined in controlled environments, and the effects on grain specific weight, protein content, Hagberg Falling Number, SDS-sedimentation volume, and sulphur content were also studied.
347 citations
TL;DR: In this paper, commercial corundum powder and a liquid-shaping approach are used for manufacturing complex hollow components and large flat windows of sintered and hot isostatically pressed Al2O3 ceramics having grain sizes of 0.4-0.6 μm at relative densities of >99.9%.
Abstract: Commercial corundum powder and a liquid-shaping approach are used for manufacturing complex hollow components and large flat windows of sintered and hot isostatically pressed Al2O3 ceramics having grain sizes of 0.4–0.6 μm at relative densities of >99.9%. High macrohardness (HV10 = 20–21 GPa) and four-point bending strength (600–700 MPa; 750–900 MPa in three-point bending) are associated with a real in-line transmission of 55%–65% through polished plates. The submicrometer microstructure and the optical properties can be retained for use at >1100°C using dopants that shift the sintering temperature to high values without additional grain growth.
302 citations
TL;DR: In this article, the effect of Ag doping on TiO2 anatase to rutile phase transformation was investigated by means of XRD, TEM, SEM, DSC-TG, and surface morphological characterization.
Abstract: Pure and Ag doped TiO2 powders were prepared by the sol-gel process. The effect of Ag doping on TiO2 anatase to rutile phase transformation was investigated by means of XRD, TEM, SEM, DSC-TG, and surface morphological characterization. It is found that the Ag doping promotes the phase transformation but has a depression effect on the anatase grain growth. The mechanism is proposed. With a suitable amount (ca. 2–6 mol%), the Ag dopant reduces anatasegrain size and increases the specific surface area of TiO2 powder, which exhibits a great potential in improving the TiO2 photocatalytic activity.
278 citations
TL;DR: In this article, the authors report on experimental evidence indicating that another crystal growth process took place in a colloidal nanocrystal system at room temperature, based on grain rotation among neighboring grains, resulting in a coherent grain-grain interface.
Abstract: The crystal growth process in colloidal nanocrystal systems is usually associated with the Ostwald-ripening mechanism. Here, we report on experimental evidence indicating that another crystal growth process took place in a colloidal nanocrystal system at room temperature. This crystal growth process is based on grain rotation among neighboring grains, resulting in a coherent grain–grain interface, which, by eliminating common boundaries, causes neighboring grains to coalesce, thereby forming a single larger nanocrystal. This phenomenon was observed in SnO2 nanocrystals (particle size ranging from 10 to 30 A).
256 citations
TL;DR: Spark plasma sintering (SPS) is a comparatively new technique as mentioned in this paper, which allows very fast heating and cooling rates, very short holding times, and the possibility to obtain fully dense samples at comparatively low sinterings temperatures, typically a few hundred degrees lower than in normal hot pressing.
251 citations
TL;DR: In this paper, microstructural evolution during thermal annealing of a cryogenically ball milled Al-7.6 at% Mg alloy with a grain size of ~25 nm was examined using differential scanning calorimetry, x-ray diffraction, and transmission electron microscopy.
224 citations
TL;DR: In this paper, the coupling between grain growth and grain-boundary diffusion creep was investigated in a polycrystal consisting of 25 grains with an average grain size of about 15 nm and a columnar grain shape.
TL;DR: In this article, an aluminum 7034 alloy was processed by equal-channel angular pressing (ECAP) at 473 K to produce an ultrafine grain size of ~0.3 μm.
TL;DR: In this article, the sintering kinetics and microstructural evolution of alumina tubes (∼17 mm length, ∼9 mm inner diameter, and ∼11 mm outer diameter) were studied by conventional and microwave heating at 2.45 GHz.
Abstract: The sintering kinetics and microstructural evolution of alumina tubes (∼17 mm length, ∼9 mm inner diameter, and ∼11 mm outer diameter) were studied by conventional and microwave heating at 2.45 GHz. Temperature during microwave heating was measured with an infrared pyrometer and was calibrated to ±10°C. With no hold at sintering temperature, microwave-sintered samples reached 95% density at 1350°C versus 1600°C for conventionally heated samples. The activation energy for microwave sintering was 85 ± 10 kJ/mol, whereas the activation energy for conventionally sintered samples was 520 ± 14 kJ/mol. Despite the difference in temperature, grains grew from ∼1.0 μm at 86% density to ∼2.6 μm at 98% density for both conventionally sintered and microwave-sintered samples. The grain size/density trajectory was independent of the heating source. It is concluded that the enhanced densification with microwave heating is not a consequence of fast-firing and therefore is not a result in the change in the relative rates of surface and grain boundary diffusion in the presence of microwave energy.
25 Oct 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effect of temperature and strain rate on the resulting recrystallised grain size was investigated and it was shown that very fine-scale microstructures (i.e. with a mean grain size smaller than 5 μm) can be easily produced by DRX during high-temperature extrusion of the AZ91 alloy.
Abstract: Microstructural changes during high-temperature extrusion and torsion of an AZ91 alloy (Mg–9Al–1Zn, wt.%) were investigated. In the experimental domain studied, dynamic recrystallisation (DRX) occurs and the effect of temperature and strain rate on the resulting recrystallised grain size was investigated. Complete recrystallisation in torsion is associated with the development of a stress plateau after softening from the peak stress, which is systematically observed in the first steps of straining. The resulting grain size can be related to the value of the peak stress. It appears that the precipitation of the Mg 17 Al 12 phase does not affect significantly the torsion behaviour of the alloy in the experimental domain investigated here. This study supports the idea that very fine-scale microstructures (i.e. with a mean grain size smaller than 5 μm) can be easily produced by DRX during high-temperature extrusion of the AZ91 alloy.
15 Sep 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the grain growth of pure carbide powders was suppressed with full densification by shortening sintering time by adding free carbon in the powder size of 4.06 μm.
Abstract: Pure WC was sintered by spark plasma sintering (SPS) process for a binderless cemented carbide application. The relative density of spark plasma sintered WC was over 98% when the SPS temperature was 1700 °C under 50 MPa pressure. Grain growth of WC could be suppressed with full densification by shortening sintering time. When the initial WC powder size was varied from 0.57 to 4.06 μm, the sintered density decreased with decreasing WC powder size. However, WC with an initial powder size of 0.57 μm could be sintered to densification by addition of free carbon. The higher amount of surface oxide in the finer WC powder is considered to have caused decarbonization during the sintering process. For WC powders of 4.06 μm, abnormal grain growth occurred when the sintering time was over 1 min if the sintering temperature was over 1700 °C. Also, with the sintering temperature and sintering time where no abnormal grain growth occurred, abnormal grain growth occurred by addition of carbon. This result shows that the abnormal grain growth in WC sintered by SPS process can be controlled by carbon addition. The abnormal grain growth in sintered WC somewhat increased fracture toughness by crack deflection.
TL;DR: In this article, the effects of annealing on the morphology and crystallization kinetics for the high-κ gate dielectric replacement candidate hafnium oxide (HfO2) were reported.
Abstract: We report the effects of annealing on the morphology and crystallization kinetics for the high-κ gate dielectric replacement candidate hafnium oxide (HfO2). HfO2 films were grown by atomic layer deposition (ALD) on thermal and chemical SiO2 underlayers. High-sensitivity x-ray diffractometry shows that the as-deposited ALD HfO2 films on thermal oxide are polycrystalline, containing both monoclinic and either tetragonal or orthorhombic phases with an average grain size of ∼8.0 nm. Transmission electron microscopy shows a columnar grain structure. The monoclinic phase predominates as the annealing temperature and time increase, with the grain size reaching ∼11.0 nm after annealing at 900 °C for 24 h. The crystallized fraction of the film has a strong dependence on annealing temperature but not annealing time, indicating thermally activated grain growth. As-deposited ALD HfO2 films on chemical oxide underlayers are amorphous, but show strong signatures of ordering at a subnanometer level in Z-contrast scannin...
TL;DR: Both cytokinins and IAA in the grains may mediate cell division in rice endosperm at early grain filling stages, and therefore regulate the sink size of the grain, whereas ABA content correlates with sink activity during the linear period of grain growth.
Abstract: Inferior spikelets usually exhibit a slower grain filling rate and lower grain weight than superior spikelets in a rice (Oryza sativa L.) panicle. This study investigated whether the variations in grain filling between the two kinds of spikelets were attributed to their sink strength and whether the sink strength was regulated by the hormonal levels in the grains. Using two field-grown rice genotypes, the division rate of endosperm cells, hormonal levels in the grains, and grain weight of both superior and inferior spikelets were determined during the grain filling period. The results showed that superior spikelets had dominance over inferior spikelets in endosperm cell division rate and cell number, grain filling and grain weight. Changes in zeatin (Z) and zeatin riboside (ZR) contents paralleled and were very significantly correlated with the cell division rate and cell number. Cell division rate and the content of indole-3-acetic acid (IAA) in the grains were also significantly correlated. Gibberellin (GAs; GA1+ GA4) content of the grains was high but ABA levels were low at the early grain filling stage. ABA increased substantially during the linear phase of grain growth and was very significantly correlated with grain dry weight during this period. Application of kinetin at 2 through 6 days post anthesis (DPA) significantly increased cell number, while spraying ABA at 11 through 15 DPA significantly increased the grain filling rate. The results suggest that differences in sink strength are responsible for variations in grain filling between superior and inferior spikelets. Both cytokinins and IAA in the grains may mediate cell division in rice endosperm at early grain filling stages, and therefore regulate the sink size of the grain, whereas ABA content correlates with sink activity during the linear period of grain growth.
TL;DR: In this paper, the formation of nanocrystalline structure (NS) in steels by various severe plastic deformation processes, such as ball milling, a ball drop test, particle impact deformation and air blast shot peening are demonstrated.
Abstract: The formation of nanocrystalline structure (NS) in steels by various severe plastic deformation processes, such as ball milling, a ball drop test, particle impact deformation and air blast shot peening are demonstrated. Layered or equiaxed nanograined region appeared near the specimen surface and dislocated cell structured region appeared interior of specimens. These regions are separated with clearly defined boundaries. The deformation induced nanograined regions have the following common specific characteristics: 1) with grains smaller than 100 nm and low dislocation density interior of grains, 2) extremely high hardness, 3) dissolution of cementite when it exist and 4) no recrystallization and slow grain growth by annealing. The deformation conditions to produce NS was discussed based on the available data in literatures. It was suggested that the most important condition is to impose a strain larger than about 7. High strain rates, low deformation temperature, multidirectional deformation, hydrostatic pressure are considered to be favorable conditions to produce NS. Introducing alloying elements, precipitates and second phase also enhance nanocrystallization by suppressing recovery. The mechanisms of the formation of sharply defined boundaries which separate nanograined structure region from dislocated cell structured region were discussed with respect to impurities, martensitic transformation and deformation. It was suggested several mechanisms may operate simultaneously in the formation of the clear boundaries.
TL;DR: In this article, the electrical properties of 3 mol% Y2O3 doped ZrO2 were measured by impedance spectroscopy as a function of grain size, and the microstructure studied by SEM and HREM.
TL;DR: In this paper, a two-dimensional numerical model of microstructural effects in brittle fracture is presented, with an aim towards the understanding of toughening mechanisms in polycrystalline materials such as ceramics.
Abstract: A two-dimensional numerical model of microstructural effects in brittle fracture is presented, with an aim towards the understanding of toughening mechanisms in polycrystalline materials such as ceramics. Quasi-static crack propagation is modelled using the extended finite element method (X-FEM) and microstructures are simulated within the framework of the Potts model for grain growth. In the X-FEM, a discontinuous function and the two-dimensional asymptotic crack-tip displacement fields are added to the finite element approximation to account for the crack using the notion of partition of unity. This enables the domain to be modelled by finite elements with no explicit meshing of the crack surfaces. Hence, crack propagation can be simulated without any user-intervention or the need to remesh as the crack advances. The microstructural calculations are carried out on a regular lattice using a kinetic Monte Carlo algorithm for grain growth. We present a novel constrained Delaunay triangulation algorithm with grain boundary smoothing to create a finite element mesh of the microstructure. The fracture properties of the microstructure are characterized by assuming that the critical fracture energy of the grain boundary (Gcgb) is different from that of the grain interior (Gci). Numerical crack propagation simulations for varying toughness ratios Gcgb/Gci are presented, to study the transition from the intergranular to the transgranular mode of crack growth. This study has demonstrated the capability of modelling crack propagation through a material microstructure within a finite element framework, which opens-up exciting possibilities for the fracture analysis of functionally graded material systems. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors used tabular SrTiO3 template particles to obtain d33 coefficients over 500 pC/N for highly textured samples (f∼ 90%) when driven at high electric fields.
Abstract: (Na1/2Bi1/2)TiO3-BaTiO3 ( pc orientation were fabricated by Templated Grain Growth (TGG) or Reactive Templated Grain Growth (RTGG) using tabular SrTiO3 template particles. The maximum electrically-induced strain was 0.26% at 70 kV/cm. d33 coefficients over 500 pC/N were obtained for highly textured samples (f∼ 90%) when driven at high electric fields. Under these conditions, the materials show considerable hysteresis in the strain—field response, even after poling. Berlincourt piezoelectric coefficients for the same samples gave d33 of 200 pC/N.
TL;DR: In this article, a nanocrystalline (∼15−20 nm) 3 mol % yttria-stabilized zirconia (3YSZ) powder is synthesized via sol−gel technique.
Abstract: Nanocrystalline (∼15−20 nm) 3 mol % yttria-stabilized zirconia (3YSZ) powder is synthesized via sol−gel technique. A reduced activation energy value of ∼13.0 ± 0.9 kJ/mol is observed for grain grow...
TL;DR: In this article, the microstructure in Y2O3-stabilized tetragonal zirconia polycrystal (Y-TZP) sintered at 1300°-1500°C was examined to clarify the role of Y3+ ions on grain growth and the formation of cubic phase.
Abstract: The microstructure in Y2O3-stabilized tetragonal zirconia polycrystal (Y-TZP) sintered at 1300°–1500°C was examined to clarify the role of Y3+ ions on grain growth and the formation of cubic phase. The grain size and the fraction of the cubic phase in Y-TZP increased as the sintering temperature increased. Both the fraction of the tetragonal phase and the Y2O3 concentration within the tetragonal phase decreased with increasing fraction of the cubic phase. Scanning transmission electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) measurements revealed that cubic phase regions in grain interiors in Y-TZP generated as the sintering temperature increased. High-resolution electron microscopy and nanoprobe EDS measurements revealed that no amorphous layer or second phase existed along the grain-boundary faces in Y-TZP and Y3+ ions segregated at their grain boundaries over a width of ∼10 nm. Taking into account these results, it was clarified that cubic phase regions in grain interiors started to form from grain boundaries and the triple junctions in which Y3+ ions segregated. The cubic-formation and grain-growth mechanisms in Y-TZP can be explained using the grain boundary segregation-induced phase transformation model and the solute drag effect of Y3+ ions segregating along the grain boundary, respectively.
TL;DR: In this paper, the formation of nanocrystalline structure (NS) on the surface of bulk steel samples by a particle impact and air blast shot peening techniques was studied.
Abstract: The formation of nanocrystalline structure (NS) on the surface of bulk steel samples by a particle impact and air blast shot peening techniques was studied. Nanocrystalline layers with several microns thick were successfully fabricated by these methods. The nanocrystalline layers produced in the present study have extremely high hardness and separated from adjacent deformed morphology region with sharp boundaries. By annealing, nanocrystalline layers showed slow grain growth without recrystallization. Those characteristics are similar to those observed in the NS produced by ball milling and a ball drop deformation. It was suggested that to produce NS by deformation a large strain is a necessary condition and a high strain rate and low temperature are favorable conditions.
TL;DR: In the case of TGG, molten salt synthesized SrTiO3 platelets were tape cast with a (Na1/2Bi 1/2)TiO 3-5.5 mol% BaTiO 2 powder and sintered at 1200°C for up to 12 hours as mentioned in this paper.
Abstract: Textured (Na1/2Bi1/2)TiO3-BaTiO3 (5.5 mol% BaTiO3) ceramics with pc (where pc denotes the pseudocubic perovskite cell) orientation were fabricated by Templated Grain Growth (TGG) and Reactive Templated Grain Growth (RTGG) using anisotropically shaped template particles. In the case of TGG, molten salt synthesized SrTiO3 platelets were tape cast with a (Na1/2Bi1/2)TiO3-5.5 mol%BaTiO3 powder and sintered at 1200°C for up to 12 h. In the RTGG approach, Bi4Ti3O12 (BiT) platelets were tape cast with a Na2CO3, Bi2O3, TiO2, and BaCO3 powder mixture and reactively sintered. The TGG approach using SrTiO3 templates resulted in >90% texture along [001] whereas the RTGG approach using BiT templates resulted in 80% texture. The grain orientation distribution along the textured direction, as measured by X-ray rocking curve, showed a full width at half maximum of ∼8° and a texture fraction of 80%.
TL;DR: The grain boundary specific conductivity and the total ionic conductivity were not significantly affected by SiO 2 additions less than 5 wt.% when samples of a similar grain size were compared.
TL;DR: In this article, the authors examined the nature of sunflower grain growth and oil quality responses to exposure to high temperature and found that the period from 12 to 19daa showed the greatest sensitivity to heat stress regarding embryo and grain weight responses, whereas the period of greatest sensitivity for oil quality was from 19 to 26daa.
TL;DR: In this article, the influence of zirconia particles addition and micro-structural coarsening, as a result of different heat treatments, on the fracture toughness of a monolithic alumina and a ZIRconia-toughened-alumina (ZTA) composite is studied.
TL;DR: In this article, a set of mechanism-based unified viscoplastic constitutive equations were developed to model the evolution of dislocation density, recrystallisation and grain size during and after hot plastic deformation.
TL;DR: In this article, a fine powder of ZnO was synthesized by the sol-gel method, which was then calcined followed by spin coating on an alumina substrate and tested for CO gas sensing.
Abstract: Fine powder of ZnO was synthesized by the sol–gel method, which was then calcined followed by spin coating on an alumina substrate and tested for CO gas sensing. With variation in the calcination temperature, the shape of gel powder changed into various morphologies: sheet, needle, and sphere. The grain growth rate increased above 700 °C and the larger grains showed higher degree of crystallization. The organic element in gel powders evaporated below 300 °C. The temperature dependence of the electrical conductance showed the sigmoidal shape, but the temperature range of the constant conductance narrowed with the decrease in the calcination temperature. The optimum sensing properties were observed for the specimen calcined at 500 °C, and it degraded with the increase in calcination temperature because of the larger grain size that limits the surface area for gas–solid reaction.