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Showing papers on "Grain growth published in 1998"


Journal ArticleDOI
TL;DR: In this paper, the authors defined recrystallization as the formation and migration of high angle grain boundaries driven by the stored energy of deformation, and grain coarsening as processes involving the migration of grain boundaries when the driving force for migration is solely the reduction of the grain boundary area itself.

475 citations


Journal ArticleDOI
TL;DR: In this paper, a model for the yield stress of ultra-fine grained materials based upon Coble creep was proposed, where a grain size distribution was incorporated into the analysis to account for a distribution of grain sizes occurring in most specimens.

428 citations


Journal ArticleDOI
TL;DR: In this paper, the morphological evolution of the amorphous towards the polycrystalline phase is investigated by transmission electron microscopy and it is interpreted in terms of a physical model containing few free parameters related to the thermodynamical properties of ammorphous silicon and to the kinetical mechanisms of crystal grain growth.
Abstract: The solid phase crystallization of chemical vapor deposited amorphous silicon films onto oxidized silicon wafers, induced either by thermal annealing or by ion beam irradiation at high substrate temperatures, has been extensively developed and it is reviewed here. We report and discuss a large variety of processing conditions. The structural and thermodynamical properties of the starting phase are emphasized. The morphological evolution of the amorphous towards the polycrystalline phase is investigated by transmission electron microscopy and it is interpreted in terms of a physical model containing few free parameters related to the thermodynamical properties of amorphous silicon and to the kinetical mechanisms of crystal grain growth. A direct extension of this model explains also the data concerning the ion-assisted crystal grain nucleation.

332 citations


Journal ArticleDOI
TL;DR: In this article, the influence of the physical and chemical deposition parameters on the nanostructure of the deposits and demonstrate that the grain size can be tuned to values between 13 and 93 nm, with rather narrow grain size distribution.
Abstract: Pulsed electrodeposition is a simple, yet versatile method for the production of nanostructured metals. For n-nickel we determine the influence of the physical and chemical deposition parameters on the nanostructure of the deposits and demonstrate that the grain size can be tuned to values between 13 and 93 nm, with rather narrow grain size distribution. The thermal stability of our n-nickel as studied by x-ray diffraction and differential thermal analysis exhibits no detectable grain growth up to temperatures of about 380 K and an initial $$\sqrt t $$ behavior at 503 K followed by a regime of anomalous grain growth. For nanocrystalline Ni1-x Cux (Monel-metal™) we demonstrate that alloy formation occurs at room temperature and that both chemical composition and grain size can be controlled by the pulse parameters and by appropriate organic additives.

239 citations


Journal ArticleDOI
TL;DR: The potential of high temperature superconductors to generate large magnetic fields and to carry current with low power dissipation at 77 K is particularly attractive for a variety of permanent magnet applications as mentioned in this paper.
Abstract: The potential of high temperature superconductors to generate large magnetic fields and to carry current with low power dissipation at 77 K is particularly attractive for a variety of permanent magnet applications. As a result large grain bulk (RE)-Ba-Cu-O ((RE)BCO) materials have been developed by melt process techniques in an attempt to fabricate practical materials for use in high field devices. This review outlines the current state of the art in this field of processing, including seeding requirements for the controlled fabrication of these materials, the origin of striking growth features such as the formation of a facet plane around the seed, platelet boundaries and (RE)2BaCuO5 (RE-211) inclusions in the seeded melt grown microstructure. An observed variation in critical current density in large grain (RE)BCO samples is accounted for by Sm contamination of the material in the vicinity of the seed and with the development of a non-uniform growth morphology at ≈ 4 mm from the seed position. (RE)Ba2Cu3O7-gd (RE-123) dendrites are observed to form and broaden preferentially within the a/b plane of the lattice in this growth regime. Finally, trapped fields in excess of 3 T have been reported in irradiated U-doped YBCO and (RE)1+xBa2-xCu3Oy (RE = Sm, Nd) materials have been observed to carry transport current in fields of up to 10 T at 77 K. This underlines the potential of bulk (RE)BCO materials for practical permanent magnet type applications.

236 citations


Journal ArticleDOI
TL;DR: In this article, a hypothesis is advanced that dynamic recrystallization of Earth materials undergoing solid state flow may represent a balance between grain size reduction and grain growth processes occurring directly in the boundary between the dislocation and diffusion creep fields.
Abstract: A hypothesis is advanced that dynamic recrystallization of Earth materials undergoing solid state flow may represent a balance between grain size reduction and grain growth processes occurring directly in the boundary between the dislocation and diffusion creep fields. Accordingly, the recrystallized grain size (D) and flow stress (σ) at steady state will be related by the equation delineating the field boundary, which in general is temperature dependent. Creep experiments on a metallic rock analogue, Magnox, yielded D=10 1.12 exp[29.3/RT]σ 1.2:3 and demonstrated that D (μm) decreases with increasing σ (MPa) and increasing temperature (T) in a manner which is in agreement with the field boundary hypothesis. If the model applies to rocks, the widely accepted idea that dynamic recrystallization can lead to major rheological weakening in the Earth may not hold. Moreover, empirical D-σ relations, used in paleo-piezometry, will need to be modified to account for temperature effects.

199 citations


Journal ArticleDOI
TL;DR: In this article, a simple computer model is developed to investigate the structural consequences of grain rotation, which include reduction in the total grain boundary energy in a specimen, and changes in the populations of the various CSL-related boundaries.

199 citations


Journal ArticleDOI
TL;DR: In this paper, a 304 type austenitic stainless steel was studied in connection with microstructural developments in compression at temperatures of 873 −1223 K (0.5 −0.7 Tm) under strain rates of 10−4 −10−1s−1.
Abstract: Warm (and hot) deformation of a 304 type austenitic stainless steel was studied in connection with microstructural developments in compression at temperatures of 873–1223 K (0.5–0.7 Tm) under strain rates of 10−4–10−1s−1. The two deformation domains can be categorized due to their different mechanical and microstructural behaviors. In the region of flow stresses lower than around 400 MPa, the deformation behaviors are typical for hot working accompanied with dynamic recrystallization (DRX). New grains are evolved mainly by dynamic bulging mechanism, which can be accelerated by the development of serrated grain boundaries and strain induced dislocation subboundaries. The relationship between dynamic grain sizes ranged from 2 to 7 μm and peak flow stress can be expressed by a power law function with a grain size exponent of −0.72. In contrast, in the region of flow stresses higher than 400 MPa, the deformation behaviors hardly depend on strain rate and temperature and so can be in the region of athermal deformation. The stress–strain curves under such warm deformation are similar to those affected only by dynamic recovery. The microstructures evolved at high strains are mainly characterized by the dense dislocation walls evolved in pancaked original grains, while grain boundary serration also takes place even at such warm deformation. Mechanisms of this microstructural evolution are discussed in combination with analysis of deformation mechanisms operating under warm deformation.

198 citations


Journal ArticleDOI
TL;DR: In this paper, the growth of ZnO nanocrystal thin films on sapphire substrates was investigated by atomic force microscopy and transmission electron microscopy, and it was concluded that the grain boundaries between nanocrystals serve not only as potential barriers confining excitons but also as cavity mirrors.
Abstract: Hexagonally shaped ZnO nanocrystal thin films were fabricated on sapphire(0001) substrates by laser molecular beam epitaxy. Nanocrystal structure was investigated by atomic force microscopy and transmission electron microscopy. Epitaxial growth of ZnO nanocrystal thin films on sapphire substrates was found to occur in a spiral and grain growth mode. The grain growth mode was interpreted by taking higher order epitaxial relationship of oxygen sublattice units between ZnO and sapphire into account. Nanocrystal size could be tuned from 50 to 200 nm controlling film thickness, growth conditions and stoichiometry of the target. The films having small nanocrystal size of about 50 nm showed excitonic stimulated emission having peak energy of 3.2 eV at room temperature with a very low threshold (24 kW cm−2). Mode transition from excitonic stimulated emission to electron hole plasma appeared above another threshold (50 kW cm−2). Well defined Fabry–Perot cavity mode was observed in the emission spectra measured from side edge of the film. It was concluded that the grain boundaries between nanocrystals serve not only as potential barriers confining excitons but also as cavity mirrors.

171 citations


Journal ArticleDOI
TL;DR: In this paper, a cellular automata (CA) technique was used to model DRX under isothermal and constant strain rate conditions using the Potts model, which is similar to the MC method.

166 citations


Journal ArticleDOI
TL;DR: In this article, an intragranular type of nanocomposite in lower CeO2 content for 0-1/mol% TiO2 doped Ce-TZP/Al2O3 system was investigated.

Journal ArticleDOI
TL;DR: In this paper, the two processes of anatase-to-rutile (A → R) transformation and grain growth would occur simultaneously and affect each other during the heat treatment of an anatase nanocrystalline powder at a high temperature.
Abstract: During the heat treatment of an anatase nanocrystalline powder at a high temperature, the two processes of anatase-to-rutile (A → R) transformation and grain growth would occur simultaneously and affect each other. With decrease of the original anatase grain size, the A → R transformation temperature range became extended on both sides, which may be partially attributed to the prevention effect of grain growth on this transformation. On the other hand, the grain growth process could be significantly enhanced by the A → R transformation, which can be ascribed to the higher atomic mobility because of the bond breakage during the transformation.

Journal ArticleDOI
TL;DR: In this article, the kinetics of microstructure and texture evolution during static recrystallization of a cold-rolled and annealed f.c. material is simulated by coupling a finite element model of microstructural deformation with a Monte Carlo simulation of recrasing.

Journal ArticleDOI
TL;DR: In this paper, the dependence of grain boundary migration on misorientation and impurity content are addressed, and their impact on the kinetics of microstructure evolution during grain growth is outlined.
Abstract: Current research on grain boundary migration in metals is reviewed. For individual grain boundaries the dependence of grain boundary migration on misorientation and impurity content are addressed. Impurity drag theory, extended to include the interaction of adsorbed impurities in the boundary, reasonably accounts quantitatively for the observed concentration dependence of grain boundary mobility. For the first time an experimental study of triple junction motion is presented. The kinetics are quantitatively discussed in terms of a triple junction mobility. Their impact on the kinetics of microstructure evolution during grain growth is outlined.

Journal ArticleDOI
TL;DR: In this paper, the authors examined grain boundary migration in ceramics and discussed the effects of solutes, pores, and liquid phases on grain boundary migrations, and their role in the development of anisotropic (anisometric) microstructures.
Abstract: During ceramic fabrication, densification processes compete with coarsening processes to determine the path of microstructural evolution. Grain growth is a key coarsening process. This paper examines grain boundary migration in ceramics, and discusses the effects of solutes, pores, and liquid phases on grain boundary migration rates. An effort is made to highlight work in the past decade that has contributed to and advanced our understanding of solute drag effects, pore-boundary interactions, and the role of liquid phases in grain growth and microstructural evolution. Anisotropy of the grain boundary mobility, and its role in the development of anisotropic (anisometric) microstructures is discussed as it is a central issue in recent efforts to produce ceramic materials with new combinations of properties and functionality.

Journal ArticleDOI
TL;DR: In this paper, a phase shift mask is used for large-grain growth of Si thin films on the glassy substrate. But the phase difference of light at the mask results in spatial modulation of light intensity at the sample surface, which triggers the lateral grain growth.
Abstract: We propose a novel excimer-laser crystallization method that uses a phase-shift mask for large-grain growth of Si thin films on the glassy substrate. Due to interference effects of the laser light, the phase difference of light at the mask results in spatial modulation of light intensity at the sample surface, which triggers the lateral grain growth. Grains as large as 7 µm could be grown by a single-shot irradiation.

Journal ArticleDOI
TL;DR: In this article, the effect of oxygen-active dopants on high-temperature oxidation performance and alumina scale microstructure was investigated using analytical electron microscopy, and it was shown that cation segregation to scale grain boundaries is not a sufficient condition for achieving beneficial oxidation performance.
Abstract: A fe-20 atom % Cr-10% Al matrix was dispersed with a wide range of oxide particulates in order to study the effect of oxygen-active dopants on high-temperature oxidation performance and alumina scale microstructure. The effects of these various cation dopants have been correlated with dopant ion segregation to the {alpha}-Al{sub 2}O{sub 3} grain boundaries using analytical electron microscopy. Elements such as Mn and V showed little effect on the oxide scale microstructure and were not observed to segregate. Elements such as Y, Nd, and Gd were found to have a positive effect on oxidation performance and segregated to scale grain boundaries, resulting in finer, more columnar {alpha}-Al{sub 2}O{sub 3} grains. However, Ti, Ta, Ca, and Nb also were found to segregate but had less of an effect on oxidation behavior. These results indicate that cation segregation to scale grain boundaries is not a sufficient condition for achieving beneficial oxidation performance. The driving force for diffusion and segregation in growing alumina scales is discussed. Based on comparisons with an alloy containing an Al{sub 2}O{sub 3} dispersion, the finer scale grain sizes observed with reactive element oxide dispersions are the result of grain growth inhibition and not a heterogeneous nucleation effect.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the kinetics, morphologies, and mechanisms involved in Reactive Isothermal Solidification (RIS) and found that the Ni3Sn4/liquid interface was not flat, containing deep grain boundary grooves, and part of the layer had crumbled into the liquid.

Journal ArticleDOI
TL;DR: In this article, the microwave heating of ceramic materials has been analyzed by solving the equations for grain growth and porosity (Svoboda and Riedel, 1992) during the late stages of sintering, coupled with the heat conduction equation and electric field equations for 1-D slabs.
Abstract: The microwave heating of ceramic materials has been analyzed by solving the equations for grain growth and porosity (Svoboda and Riedel, 1992) during the late stages of sintering, coupled with the heat conduction equation and electric field equations for 1-D slabs. Microwave power absorption and heating profiles have been calculated for $Al_2O_3$ and Sic in the absence of sintering, and calculations have been cam'ed out to study the effect of increasing dielectric loss of $Al_2O_3$ as a function of temperature. A comparison of the densification and grain growth for $Al_2O_3$ during microwave and conventional sintering indicates that within the framework of the present model, there is no difference between the two heating modes during the late stages of sintering.

Journal ArticleDOI
TL;DR: In this article, an equal-channel angular (ECA) pressing procedure was used to obtain high-strain-rate superplasticity in ultrafine-grained materials.
Abstract: Ultrafine grain sizes were introduced into samples of an Al-3 pct Mg solid solution alloy and a cast Al-Mg-Li-Zr alloy using the process of equal-channel angular (ECA) pressing. The Al-3 pct Mg alloy exhibited a grain size of ∼0.23 µm after pressing at room temperature to a strain of ∼4, but there was significant grain growth when the pressed material was heated to temperatures above ∼450 K. The Al-Mg-Li-Zr alloy exhibited a grain size of ∼1.2 µm, and the microstructure was heterogeneous after pressing to a strain of ∼4 at 673 K and homogeneous after pressing to a strain of ∼8 at 673 K with an additional strain of ∼4 at 473 K. The heterogeneous material exhibited superplastic-like flow, but the homogeneous material exhibited high-strain-rate superplasticity with an elongation of >1000 pct at 623 K at a strain rate of 10−2 s−1. It is concluded that a homogeneous microstructure is required, and therefore a high pressing strain, in order to attain high-strain-rate superplasticity (HSR SP) in ultrafine-grained materials.

Journal ArticleDOI
TL;DR: In this paper, a semi-quantitative model to simulate the effect of orientation pinning on the evolution of recrystallisation textures is introduced, and the results are discussed in view of growth selection and the 40° ˚ ǫ 111 −1 −1 orientation relationship.

Journal ArticleDOI
TL;DR: In this article, a new model of development of the Goss texture during the process of the secondary recrystallization of electrical steels, was proposed based on the assumption that the high-energy boundary has a high mobility.

Journal ArticleDOI
TL;DR: In this article, the effect of rolling reduction and annealing conditions on the sharpness of the cube texture, the incidence of other orientations, the grain size and the surface topography was investigated.
Abstract: The biaxial textures created in metals by rolling and annealing make them useful substrates for the growth of long lengths of biaxially textured material. The growth of overlayers such as high-temperature superconductors requires flat substrates with a single, sharp texture. A sharp cube texture is produced in high-purity Ni by rolling and annealing. We report the effect of rolling reduction and annealing conditions on the sharpness of the cube texture, the incidence of other orientations, the grain size and the surface topography. A combination of high reduction and high-temperature annealing in a reducing atmosphere leads to >99% cube texture, with a mosaic of about the rolling direction, about the transverse direction, and about the normal direction.

Journal ArticleDOI
TL;DR: In this paper, nanostructured powders with compositions corresponding to W-20%Cu and W-30%Cu were prepared by mechanical alloying, and the microstructure and grain size of as-milled and annealed powders were analyzed by transmission electron microscopy.

Journal ArticleDOI
TL;DR: In this paper, the authors used molecular-dynamics simulations to study grain-boundary diffusion creep of a model polycrystalline silicon microstructure and found that under relatively high tensile stresses these microstructures exhibit steady-state diffusion creep that is homogenous (i.e., involving no grain sliding).
Abstract: Molecular-dynamics (MD) simulations are used, for the first time, to study grain-boundary diffusion creep of a model polycrystalline silicon microstructure. Our fully dense model microstructures, with a grain size of up to 7.5 nm, were grown by MD simulations of a melt into which small, randomly oriented crystalline seeds were inserted. In order to prevent grain growth and thus to enable steady-state diffusion creep to be observed on a time scale accessible to MD simulations (of typically 10-9s), our input microstructures were tailored to (i) have a uniform grain shape and a uniform grain size of nm dimensions and (ii) contain only high-energy grain boundaries which are known to exhibit rather fast, liquid-like self-diffusion. Our simulations reveal that under relatively high tensile stresses these microstructures, indeed, exhibit steady-state diffusion creep that is homogenous (i.e., involving no grain sliding), with a strain rate that agrees quantitatively with that given by the Coble-creep formula.

Journal ArticleDOI
TL;DR: In this article, the authors observed the formation of heteroepitaxialinterfacial layers between silvernanoparticles and a single crystalcoppersurface by a phenomenon they termed as contact epitaxy.
Abstract: We have observed the formation of heteroepitaxialinterfacial layers between silvernanoparticles and a single crystalcoppersurface by a phenomenon we term “contact epitaxy.” Upon depositingAgnanoparticles (5–20 nm diameter) onto clean (001) Cu in an ultrahigh vacuum in situ transmission electron microscope, a thin (111)-oriented layer of Ag was detected at the interface between the substrate and particles. Molecular dynamics simulations reveal that the epitaxial layers form within picoseconds of impact, with rapid alignment arising from mechanical relaxation of the highly stressed interface formed upon initial contact. The simulations also show that multiple grains form in the nanoparticle as a consequence of this relaxation process. The unique structure of the nanoparticles, induced by contact epitaxy, is expected to significantly influence physical properties such as interfacial bonding, diffusion, chemical activity, and electrical transport, as well as forming a nucleus for grain growth and epitaxy which we also observe. Due to its simple origin, the phenomenon should also apply to materials systems beyond the field of nanoparticles with implications for cluster deposition, adhesion, rheology, and catalysis.

Journal ArticleDOI
TL;DR: In this paper, the influence of R2O3 substitution on the structure, magnetic and electrical properties of LiZn ferrite is examined, and the results reveal that by introducing a relatively small amount of R 2O3 (R=Yb, Er, Dy, Tb, Gd and Sm) instead of Fe 2 O3, an important modification of both structure and properties can be obtained.

Journal ArticleDOI
TL;DR: In this paper, Si crystallites on glass of several tens of mm in length were obtained via sequential lateral solidification using a copper vapor laser, and they were used to obtain Si crystallite on glass.
Abstract: Understanding nucleation and growth of crystalline Si films on glass is of prime importance in order to tailor and optimize semiconductor properties for electronic devices such as solar cells. Commercial glass limits the maximum processing temperature of Si films to 600 C. Solid phase and laser crystallization, or a combination of both techniques, are thus primarily used to crystallize Si films on glass. While random nucleation and growth processes always result in the formation of a log± normal size distribution, control of nucleation sites allows one to determine the location of grain growth or even the crystallographic orientation of grains. Via sequential lateral solidification using a copper vapor laser, we obtain Si crystallites on glass of several tens of mm in length.

Journal ArticleDOI
Sung-Min Lee1, Suk-Joong L. Kang1
TL;DR: Based on the pore filling model and previous calculations, a new liquid-phase sintering theory has been developed for compacts containing isolated pores with size distribution in this article.

Journal ArticleDOI
TL;DR: The effect of three aliovalent cations, Nb 5+, La 3+ and Co 2+, on the grain growth kinetics of nearly fully dense BaTiO 3 (Ba/Ti atomic ratio = 1.001) was measured in O 2 at 1300 °C and for dopant concentrations of up to 1.25 atomic per cent (at%).
Abstract: The effect of three aliovalent cations, Nb 5+ , La 3+ and Co 2+ , on the grain growth kinetics of nearly fully dense BaTiO 3 (Ba/Ti atomic ratio = 1.001) was measured in O 2 at 1300 °C and for dopant concentrations of up to 1.25 atomic per cent (at%). For the donor cation Nb 5+ , the boundary mobility initially increased with cation concentration but then decreased markedly above a doping threshold of 0.3–0.5 at%. The boundary mobility of the BaTiO 3 doped with the acceptor cation Co 2+ decreased monotonically with dopant concentration. At a cation concentration of 0.75 at%, the boundary mobility was reduced by a factor of approximately 25, 10 and 50 times by Nb 5+ , La 3+ and Co 2+ , respectively. A major role of the dopants is seen to be their ability to influence the boundary mobility. The effects of the dopants on the boundary mobility are discussed in terms of the defect chemistry and the space-charge concept.