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Showing papers on "Grain size published in 2003"


Journal ArticleDOI
05 Sep 2003-Science
TL;DR: Using molecular dynamics simulations with system sizes up to 100 million atoms to simulate plastic deformation of nanocrystalline copper, it is shown that the flow stress and thus the strength exhibit a maximum at a grain size of 10 to 15 nanometers.
Abstract: We used molecular dynamics simulations with system sizes up to 100 million atoms to simulate plastic deformation of nanocrystalline copper. By varying the grain size between 5 and 50 nanometers, we show that the flow stress and thus the strength exhibit a maximum at a grain size of 10 to 15 nanometers. This maximum is because of a shift in the microscopic deformation mechanism from dislocation-mediated plasticity in the coarse-grained material to grain boundary sliding in the nanocrystalline region. The simulations allow us to observe the mechanisms behind the grain-size dependence of the strength of polycrystalline metals.

1,289 citations


Journal ArticleDOI
18 Apr 2003-Science
TL;DR: Comparison with previously reported membranes shows that these microstructurally optimized films have superior performance for the separation of organic mixtures with components that have small differences in size and shape, such as xylene isomers.
Abstract: A seeded growth method for the fabrication of high-permeance, high-separation-factor zeolite (siliceous ZSM-5, [Si 96 O 192 ]-MFI) membranes is reported. The method consists of growing the crystals of an oriented seed layer to a well-intergrown film by avoiding events that lead to a loss of preferred orientation, such as twin overgrowths and random nucleation. Organic polycations are used as zeolite crystal shape modifiers to enhance relative growth rates along the desirable out-of-plane direction. The polycrystalline films are thin (∼1 micrometer) with single grains extending along the film thickness and with large in-plane grain size (∼1 micrometer). The preferred orientation is such that straight channels with an open diameter of ∼5.5 angstroms run down the membrane thickness. Comparison with previously reported membranes shows that these microstructurally optimized films have superior performance for the separation of organic mixtures with components that have small differences in size and shape, such as xylene isomers.

959 citations


Journal ArticleDOI
TL;DR: In this article, a transport model for mixed sand/gravel sediments is presented, which uses the full size distribution of the bed surface, including sand, and incorporates a nonlinear effect of sand content on gravel transport rate not included in previous models.
Abstract: We present a transport model for mixed sand/gravel sediments. Fractional transport rates are referenced to the size distribution of the bed surface, rather than subsurface, making the model completely explicit and capable of predicting transient conditions. The model is developed using a new data set of 48 coupled observations of flow, transport, and bed surface grain size using five different sediments. The model incorporates a hiding function that resolves discrepancies observed among earlier hiding functions. The model uses the full size distribution of the bed surface, including sand, and incorporates a nonlinear effect of sand content on gravel transport rate not included in previous models. The model shares some common elements with two previous surface-based transport models, but differs in using the full surface size distribution and in that it is directly developed from a relatively comprehensive data set with unambiguous measurement of surface grain size over a range of flow, transport rate, and sediments.

803 citations


Journal ArticleDOI
TL;DR: In this paper, a simple model is proposed to explain the development of a homogeneous microstructure in high pressure torsion (HPT) processing of pure nickel samples, showing that the distributions of grain boundary misorientations are similar in the center and at the periphery of the samples.

704 citations


Journal ArticleDOI
TL;DR: In this article, the mechanisms of deformation and damage evolution in electrodeposited, fully dense, nanocrystalline Ni with an average grain size of ~30 nm and a narrow grain size distribution were investigated by recourse to (i) tensile tests performed in situ in the transmission electron microscope and (ii) microscopic observations made at high resolution following ex situ deformation induced by compression, rolling and nanoindentation.

689 citations


Journal ArticleDOI
TL;DR: In this paper, a simple computational model, predicated on the assumption that a rate-sensitive grain boundary affected zone exists, is shown to explain the observed effect of grain size on the rate-dependent plastic response.

551 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied the mechanical behavior of consolidated iron with average grain sizes from tens of nanometers to tens of microns under uniaxial compression over a wide range of strain rates.

496 citations


Journal ArticleDOI
TL;DR: In this paper, the role of solid solution additions of ~13 at% W were considered with respect to the structure and mechanical properties of electrodeposited Ni alloys with grain sizes below 10 nm.

460 citations


Journal ArticleDOI
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


Journal ArticleDOI
TL;DR: Ni-Zn ferrite powders with a nominal composition of Ni 0.5 Zn 0.4 Fe 2 O 4 were prepared by combustion synthesis, using urea as fuel.

378 citations


Journal ArticleDOI
TL;DR: In this paper, a series of tests were conducted to trigger rainfall-induced landslides using a small flume, and the effects of grain size on pore-pressure generation and failure behavior of a landslide mass were analyzed.

Journal ArticleDOI
TL;DR: In this paper, a simple model for the strength in this regime of grain sizes is developed from classical dislocation theory, based on the bow-out of a dislocation from a grain boundary dislocation source.

Journal ArticleDOI
TL;DR: In this article, the authors modeled grain boundaries in polycrystalline ZnO TFTs and performed simulation of the device by using a two-dimensional device simulator in order to determine the grain boundary effects on device performance.
Abstract: Thin-film transistors (TFTs) made of transparent channel semiconductors such as ZnO are of great technological importance because their insensitivity to visible light makes device structures simple. In fact, there have been several demonstrations of ZnO TFTs achieving reasonably good field effect mobilities of 1–10 cm2/V s, but the overall performance of ZnO TFTs has not been satisfactory, probably due to the presence of dense grain boundaries. We modeled grain boundaries in ZnO TFTs and performed simulation of a ZnO TFT by using a two-dimensional device simulator in order to determine the grain boundary effects on device performance. Polycrystalline ZnO TFT modeling was started by considering a single grain boundary in the middle of the TFT channel, formulated with a Gaussian defect distribution localized in the grain boundary. A double Schottky barrier was formed in the grain boundary, and its barrier height was analyzed as a function of defect density and gate bias. The simulation was extended to TFTs with many grain boundaries to quantitatively analyze the potential profiles that developed along the channel. One of the main differences between a polycrystalline ZnO TFT and a polycrystalline Si TFT is that the much smaller nanoscaled grains in a polycrystalline ZnO TFT induces a strong overlap of the double Schottky barriers with a higher activation energy in the crystallite and a lower barrier potential in the grain boundary at subthreshold or off-state region of its transfer characteristics. Through the simulation, we were able to estimate the density of total trap states localized in the grain boundaries for polycrystalline ZnO TFT by determining the apparent mobility and grain size in the device.

Journal ArticleDOI
TL;DR: In this paper, a dislocation model that predicts the value of dmin as a function of material parameters, such as hardness, melting temperature, and stacking fault energy, has been developed, based on the concept that dmin is governed by a balance between the hardening rate introduced by dislocation generation and the recovery rate arising from dislocation annihilation and recombination.

Journal ArticleDOI
TL;DR: In this paper, the effect of grain size in the range of nm to mm on the deformation kinetics of Cu at 77-373 K was analyzed to determine the influence of grain sizes on the strain rate-controlling mechanism.
Abstract: Data on the effect of grain size d in the range of nm to mm on the plastic deformation kinetics of Cu at 77–373 K are analyzed to determine the influence of grain size on the strain rate-controlling mechanism. Three grain size regimes were identified: Regimes I (d≈10−6–10−3 m), II (d≈10−8–10−6 m) and III (d<∼10−8 m). A dislocation cell structure characterizes Regime II, which no longer occurs in Regime II. The absence of all intragranular dislocation activity characterizes Regime III. The following mechanisms were concluded to be rate-controlling for : (a) Regime I, intersection of dislocations; (b) Regime I, grain boundary shear promoted by dislocation pile-ups; and (c) Regime III, grain boundary shear. The major effect of grain size on the intersection mechanism in Regime I is on the mobile and forest dislocation densities; the effect in Regime II is on the number of dislocations and on the number of grain boundary atom sites; the effect in Regime III is on the number of grain boundary atom sites. The transition grain size from one regime to another depends on the strain rate and temperature. Crystallographic texture is also important.

Journal ArticleDOI
01 Jan 2003-Wear
TL;DR: In this paper, the effect of carbide grain size on the wear behavior of WC-Co coatings was examined using dry sliding friction and wear tests using sintered alumina as the mating material.

Journal ArticleDOI
TL;DR: In this paper, surface mechanical attrition treatment (SMAT) was applied to a pure iron plate and a nanometer-grained surface layer without porosity and contamination was fabricated.

Journal ArticleDOI
TL;DR: In this paper, the formation of homogeneous nanocrystalline structure by nano-coalescence of amorphous NiTi subjected to high pressure torsion is demonstrated.
Abstract: The formation of homogeneous nanocrystalline structure by nanocrystallization of amorphous NiTi subjected to high pressure torsion is demonstrated. Structural evolution during annealing was investigated and homogeneous nanocrystalline structures with different grain sizes have been obtained by controlled annealing. Nanocrystallization results in the record value of room temperature strength for this material equal to 2650 MPa with an elongation to failure of about 5%. At elevated temperatures of (0.4…0.5)Tm nanocrystalline nitinol showed a high ultimate strength with sufficient elongation (up to 200%). The observation that the shape and the size of grains after deformation remain close to that of the initial state suggests that in nanocrystalline NiTi such mechanism as grain boundary sliding and grain rotation are active and the generation and motion of dislocations play the role of accommodation of stress concentration.

Journal ArticleDOI
TL;DR: In this paper, the XRD patterns show that the films are of hexagonal phase with preferred (0.0.2) orientation and the grain size increases with the thickness of the film.

Journal ArticleDOI
TL;DR: In this article, the grain size determined by the Warren-Averbach analysis is compared with the lower bound grain size (e.g., 50 to 100 nm) observed experimentally.
Abstract: The Warren-Averbach (WA) analysis and other simplified methods that are commonly used to determine the grain size of nanocrystalline materials are discussed in terms of accuracy and applicabilities. The nanocrystalline materials used in the present study are prepared by cryomilling of A1 powders and subsequent consolidation (hot isostatic pressing and extrusion). Transmission electron microscopy observations of the as-extruded nanocrystalline A1 reveal a bimodal distribution of grain sizes centered around 50 to 100 nm and 250 to 300 nm. It is shown that the grain size determined by the WA analysis agrees with the lower bound grain size (e.g., 50 to 100 nm) observed experimentally. In the case of the integral method, it is useful to use a parabolic (Cauchy-Gaussian (CG)) relationship to approximate instrumental broadening and separate the intrinsic broadening. Compared to the Cauchy-Cauchy (CC) and Gaussian-Gaussian (GG) approximations, this is shown to give the best results. In addition, the reliability of the Scherrer equation is also discussed.

Journal ArticleDOI
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.

Journal ArticleDOI
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.

Journal ArticleDOI
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.

Journal ArticleDOI
06 Jun 2003-Science
TL;DR: It is proposed that local shear planes formed around clustered grains that, because of their particular misorientation, cannot participate in the grain boundary accommodation processes necessary to sustain plastic deformation, raises the expectation that general high-angle grain boundaries are necessary for good ductility.
Abstract: Tensile experiments of fully dense nanocrystalline structures with a mean grain size of less than 100 nanometers demonstrate a considerable increase in hardness but a remarkable drop in elongation-to-failure, indicating brittle behavior. However, dimple structures are often observed at the fracture surface, indicating some type of ductile fracture mechanism. Guided by large-scale atomistic simulations, we propose that these dimple structures result from local shear planes formed around clustered grains that, because of their particular misorientation, cannot participate in the grain boundary accommodation processes necessary to sustain plastic deformation. This raises the expectation that general high-angle grain boundaries are necessary for good ductility.

Journal ArticleDOI
TL;DR: In this article, the dynamic recrystallization (DRX) behavior of Nb and Nb-Ti microalloyed steels has been investigated, and it has been observed that decreasing the values of the Zener-Hollomon parameter and the initial grain size, promotes dynamic re-stallization.
Abstract: The dynamic recrystallization (DRX) behavior of Nb and Nb–Ti microalloyed steels has been investigated. It has been observed that the initial austenite grain size, the amount of microalloying elements in solid solution, and the deformation conditions (temperature and strain rate), affect dynamic recrystallization kinetics. To characterize the dynamic recrystallization behavior of the microalloyed austenite, continuous torsion tests were carried out after reheating the specimens at different temperatures between 1000 and 1420 °C, leading to a wide range of initial grain sizes, from 16 to 805 μm. It has been observed that decreasing the values of the Zener–Hollomon parameter and the initial grain size, promotes dynamic recrystallization. Microalloying elements in solid solution produce a retardation of dynamic recrystallization, resulting in higher values of the characteristic critical, e c , and peak, e p , strains. A corrective factor has been applied to quantify the retardation produced by the increase in the amount of Nb and Ti dissolved as the reheating temperature increases. In this manner, it has been possible to propose a unique relationship to predict the e p peak strain for both steels.

Journal ArticleDOI
TL;DR: In this article, the Guglielmi adsorption mechanism was applied to the electroplating of the ultra-fine SiC with Ni, and the embedded SiC concentration can be increased either by increasing electrical current density or by raising the pH of the suspension to 5.

Journal ArticleDOI
Andreas Krell1, Paul Blank1, Hongwei Ma1, Thomas Hutzler1, Manfred Nebelung1 
TL;DR: In this paper, the authors developed a method to associate minimum grain sizes at highest densities with the lowest population of macro-defects by using powders with particle sizes in the range of 100-200 nm.
Abstract: Sintered corundum components with submicrometer grain sizes exhibit properties which enable numerous new applications. Wet powder processing is developed to associate minimum grain sizes at highest densities with the lowest population of macrodefects. A closest ratio of powder particle size and sintered grain size is important for obtaining most fine-grained microstructures. This target was approached best by using powders with particle sizes in the range of 100-200 nm rather than with smaller nanoparticles.

Journal ArticleDOI
TL;DR: In this paper, the authors examined the one-dimensional stress-strain behavior of sand at effective stresses as high as 50 MPa and found that minor grain corner crushing starts at stresses of 2-8 MPa, and the lowest yield stress value occurs in the coarser carbonate sand and the highest in the chert-rich sands.
Abstract: This study examines the one-dimensional stress-strain behaviour of sand at effective stresses as high as 50 MPa. Experiments were performed on 22 sands (approx. 150 tests) with different grain size, uniformity coefficient, angularity, density, grain mineralogy, and clay content. The results show that minor grain corner crushing starts at stresses of 2-8 MPa. The point of maximum curvature (yield point) in the porosity (n) versus logarithm of vertical ef- fective stress (σv ' ) curve defines the initiation of marked particle crushing. The stress at the yield point varies between 3 and 31 MPa depending on sand characteristics. A low yield stress is indicative of high porosity loss in the interval of intermediate stress (5-25 MPa). The yield stress is low when the grain size is large, grains are angular, grain strength is low, and uniformity coefficient is low. The lowest yield stress value occurs in the coarser carbonate sand, and the highest in the chert-rich sands. The sands rich in clays are highly compressible up to 25 MPa. At stresses higher than 10 MPa, the coarser biogenic carbonate sands maintain higher porosities than the other sands. This can be explained by the fact that coarser biogenic carbonate sands have low yield stresses due to high angularity and low grain strength and initially there is local grain crushing at grain contacts. This increases the area of the grain contacts, so the coarser carbonate sands become less compressible at higher stresses. Within the high stress range (25-50 MPa) the porosity loss differences related to grain size, grain shape, grain mineralogy, and sand uniformity coefficient are significantly re- duced. Hence the greater compressibility of lithic and carbonate sands becomes less evident in the high-stress interval as the grain size increases.

Patent
Stephen J. Hudgens1, Tyler Lowrey1
04 Aug 2003
TL;DR: A phase change material may be processed to reduce its micro-crystalline grain size and may also be processed in order to increase the crystallization or set programming speed of the material as mentioned in this paper.
Abstract: A phase change material may be processed to reduce its microcrystalline grain size and may also be processed to increase the crystallization or set programming speed of the material. For example, material doped with nitrogen to reduce grain size may be doped with titanium to reduce crystallization time.

Journal ArticleDOI
TL;DR: In this paper, the authors developed a modeling framework for predicting the visco-plastic deformation, microstructural evolution and texture evolution in polycrystalline materials during the equal channel angular extrusion (ECAE) process, a discontinuous process of severe shear straining.
Abstract: In this work, we develop a modeling framework for predicting the visco-plastic deformation, microstructural evolution (distributions of grain shape and size) and texture evolution in polycrystalline materials during the equal channel angular extrusion (ECAE) process, a discontinuous process of severe shear straining. The foundation of this framework is a visco-plastic self-consistent (VPSC) scheme. We consider a 90° die angle and simulate ECAE up to four passes for four processing routes, (A, C, B A and B C , as denoted in the literature) for an FCC polycrystalline material. We assume that the FCC single crystal has a constant critical resolved shear stress (CRSS), so that hardening by dislocation activity is suppressed, and the influence of grain shape distribution and texture as well as their interaction can be isolated. Many deformation microstructural features, such as grain size and shape distribution, texture, and geometric hardening–softening, were highly dependent on processing route. Using a grain subdivision criterion based on grain shape, route A was the most effective, then route B A and route B C and lastly route C, the least effective for grain size refinement, in agreement with redundant strain theory. For producing refined equiaxed grains, route B C was more effective than routes B A and A. We show that grain–grain interactions tend to weaken texture evolution and consequently geometric hardening and softening in all routes.