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Showing papers on "Grain size published in 1996"


Journal ArticleDOI
TL;DR: In this paper, it has been shown that submicrometer-grained structures may be produced in a wide range of materials (e.g. pure metals, metallic alloys including superalloys, intermetallics, semiconductors) by subjecting these materials to a very high plastic strain using either equal-channel angular (ECA) pressing or torsion straining under high pressure.

1,655 citations


Journal ArticleDOI
TL;DR: In this article, the results of an investigation into the grain-size dependence of lattice structure for barium titanate (BaTiO) ceramics prepared by a sol-gel method were reported.
Abstract: We report the results of an investigation into the grain-size dependence of lattice structure for barium titanate (${\mathrm{BaTiO}}_{3}$) ceramics prepared by a sol-gel method. Raman and infrared spectroscopy, x-ray diffraction, and differential scanning calorimetry were used in combination with electron microscopy to study the evolution of lattice structure and phase transformation behavior with heat treatment and grain growth from the nano scale to the micron scale for ${\mathrm{BaTiO}}_{3}$ polycrystals. Raman spectroscopy and optical second-harmonic-generation measurements indicated the onset of local room-temperature acentric crystal symmetry with heat treatment and crystallite growth, well before the observation of any tetragonal structure by x-ray diffraction. Analysis of the room-temperature Raman spectra for ultrafine grain (grain size 0.1 \ensuremath{\mu}m) polycrystals suggested that a locally orthorhombic structure preceded the globally tetragonal form with grain growth. In support of this observation, differential scanning calorimetry suggested the orthorhombic-tetragonal phase transformation shifts up through room temperature with decreasing grain size. Hot-stage transmission electron microscopy studies revealed that fine grain (grain size \ensuremath{\approxeq}0.1 \ensuremath{\mu}m) ceramics, which showed a thermal anomaly associated with the cubic-tetragonal phase transformation, were untwinned at room temperature, as well as on cycling through the normal Curie temperature, suggesting a single-domain state for individual grains. The findings are discussed in light of a number of possible causes, including the presence of processing-related hydroxyl defects and the effect of elastic constraints on phase transformation behavior for ${\mathrm{BaTiO}}_{3}$ grains in a polycrystalline microstructure. \textcopyright{} 1996 The American Physical Society.

814 citations


Journal ArticleDOI
TL;DR: In this paper, structural evolutions in an Armco iron subjected to severe plastic deformation by torsion under high pressure are anlysed with conventional and high resolution electron microscopes.

597 citations


Journal ArticleDOI
TL;DR: The grain growth during film formation or during post-deposition annealing can play a dominant role in defining these microstructural characteristics, and therefore, the mechanical properties of polycrystalline thin films as discussed by the authors.
Abstract: The mechanical properties of polycrystalline thin films with thickness of 1 μm or less depend strongly on the grain geometry, the grain size, and the way in which the crystallographic orientations of the grains are distributed. Grain growth during film formation or during post-deposition annealing can play a dominant role in defining these microstructural characteristics, and therefore, the mechanical properties of films. Stress can suppress or promote grain growth. In the latter case, stress promotes texture evolution during grain growth. Grain growth can serve as a stress relief mechanism in both elastically isotropic and anisotropic materials, and can also promote plastic yielding.

488 citations


Journal ArticleDOI
TL;DR: In this paper, an Al-3% Mg solid solution alloy was subjected to intense plastic deformation, using either equal-channel angular (ECA) pressing or torsion straining, to produce grain sizes in the submicrometer range.

444 citations


Journal ArticleDOI
TL;DR: In this article, a study of the ferroelastic domain size variations with grain sizes in Pb(Zr,Ti)O3[PZT] ferroelectric ceramic has been conducted.

427 citations


Journal ArticleDOI
TL;DR: In this article, the control of grain boundary segregation through purity, microstructure, and thermal history is discussed from the objective of engineering the grain-boundary impedance of polycrystalline ionic conductors.
Abstract: Solute segregation at grain boundaries has been correlated with grain-boundary conductivity in high-purity 15-mol%-CaO-stabilized ZrO2. STEM measurements of solute coverage show that the segregation of impurity silicon (present at bulk levels 103 at 500°C. At the lowest levels of segregation achieved, <0.1 monolayer, σspgb remains ∼102 less, and possibly represents an “intrinsic” limiting value for the grain boundary. Comparison with Y2O3-doped ZrO2 suggests similar behavior in this system. The control of grain-boundary segregation through purity, microstructure, and thermal history is discussed from the objective of engineering the grain-boundary impedance of polycrystalline ionic conductors.

415 citations


Journal ArticleDOI
TL;DR: In this paper, a low-temperature excimer-laser-crystallization process was proposed to produce a previously unattainable directionally solidified microstructure in thin Si films.
Abstract: We report on a low‐temperature excimer‐laser‐crystallization process that produces a previously unattainable directionally solidified microstructure in thin Si films. The process involves (1) inducing complete melting of selected regions of the film via irradiation through a patterned mask, and (2) precisely controlled between‐pulse microtranslation of the sample with respect to the mask over a distance shorter than the single‐pulse lateral solidification distance, so that lateral growth can be extended over a number of iterative steps. Grains up to 200 μm in length were demonstrated; in principle, grains of unlimited length can be produced. We discuss how the technique can be extended to produce large single‐crystal regions on glass substrates.

374 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that unique defect thermodynamics and transport properties result for oxides of a few nanometers crystallite size, which are attributed to a dominant role of interfacial defect formation.
Abstract: It is shown that unique defect thermodynamics and transport properties result for oxides of a few nanometers crystallite size. Fully‐dense CeO2−x polycrystals of ∼10 nm grain size were synthesized, and their electrical properties compared with those of samples coarsened from the same material. The nanocrystals showed reduced grain boundary resistance, 104 higher electronic conductivity, and less than one‐half the heat of reduction of its coarse‐grained counterpart. These properties are attributed to a dominant role of interfacial defect formation.

354 citations


Journal ArticleDOI
TL;DR: In this paper, a mathematically simple kinetic model was proposed to simulate the porosity loss in sandstones as a function of temperature history and the amount of precipitated quartz cement.
Abstract: A mathematically simple kinetic model simulates quartz cementation and the resulting porosity loss in quartzose sandstones as a function of temperature history. Dissolved silica is considered to be sourced from quartz dissolution at stylolites or individual quartz grain contacts containing clay or mica, and diffuses short distances to sites of precipitation on clean quartz surfaces. The modeled sandstone volume is located between stylolites, and no quartz dissolution or grain interpenetration takes place within this volume. After quartz cementation starts, compactional porosity loss is typically minor, and porosity loss within the modeled sandstone volume is therefore considered to be equal to the volume of precipitated quartz cement. The quartz cementation process is mod led as a precipitation rate-controlled reaction where quartz precipitation rate per unit time and surface area can be expressed by an empirically determined logarithmic function of temperature. When the sandstone's temperature history is known, precipitation rate per unit time and surface area can be expressed as a function of time, and the amount of quartz cement precipitated within a certain time interval can be calculated by multiplying the precipitation rate function with the surface area available for quartz precipitation and integrating with respect to time. Because quartz surface area will change as quartz cement precipitation proceeds, the calculations are performed for short time steps, and quartz surface area is adjusted after each time step. The total amount of quartz cement p ecipitated during a sandstone's burial history and the corresponding porosity loss are found by taking the sum of the increments of quartz cement precipitated during each time step. The effect of variation in parameters such as grain size, detrital quartz content, abundance of clay or other grain coatings, prequartz cementation porosities, and temperature history is easily simulated with the presented algorithm. This flexibility is illustrated by presenting calculated histories of quartz cementation and porosity loss for sandstones with a range of grain sizes, framework grain compositions, degree of clay coat development, prequartz cementation porosities, and temperature histories.

335 citations


Journal ArticleDOI
TL;DR: The long axes of the hemicylinders lie parallel in grains which typically extend over (500 nm) 2 to (1000 nm)2, but the grain size can be reduced by adsorption of other species from solution as discussed by the authors.
Abstract: The aggregated structure of sodium dodecyl sulfate (SDS) adsorbed to the graphite−solution interface has been determined. Atomic force microscopy reveals that SDS adsorbs in periodic structures when the solution concentration is in the range 2.8−81 mM. Using previously obtained adsorption isotherms, we deduce that these structures are hemicylindrical, but we are not able to determine their length. The long axes of the hemicylinders lie parallel in grains which typically extend over (500 nm)2 to (1000 nm)2, but the grain size can be reduced by adsorption of other species from solution. Two basic types of grain boundaries have been identified: broad boundaries, where the periodicity of both grains continue into the boundary for several periods, and narrow boundaries, where one or both of the hemicylindrical arrays terminate within a short distance. The period within each grain decreases when the concentration of SDS or the concentration of added NaCl is increased and approaches the diameter of bulk micelle...

Journal ArticleDOI
TL;DR: The microstructural stability of an Al 3%Mg solid solution alloy with a submicrometer-grained (SMG) structure (∼ 0.2 μm) was evaluated using both static annealing and transmission electron microscopy over a range of temperatures from 443 to 803 K and differential scanning calorimetry (DSC) up to 773 K.

Journal ArticleDOI
TL;DR: In this article, a series of measurements on thin Ce 0.8 Gd 0.2 O 2 − δ ceramic electrolytes with a range of different grain size distributions were used to separate grain interior and grain boundary conductivities.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the abnormal grain growth (AGG) behavior is not linearly dependent on the driving force arising from the grain size difference, but the growth rate is expected to increase abruptly at a critical supersaturation.
Abstract: If the grains dispersed in a liquid matrix are spherical, their surface atomic structure is expected to be rough (diffuse), and their coarsening has been observed to be controlled by diffusion in the matrix. They do not, furthermore, undergo abnormal growth. On the other hand, in some compound material systems, the grains in liquid matrices are faceted and often show abnormal coarsening behavior. Their faceted surface planes are expected to be singular (atomically flat) and therefore grow by a defect-assisted process and two-dimensional (2-D) nucleation. Contrary to the usual coarsening the-ories, their growth velocity is not linearly dependent on the driving force arising from the grain size difference. If the growth of the faceted grains occurs by 2-D nucleation, the rate is expected to increase abruptly at a critical supersaturation, as has been observed in crystal growth in melts and solutions. It is proposed that this growth mechanism leads to the abnormal grain coarsening. The 2-D nucleation theory predicts that there is a threshold initial grain size for the abnormal grain growth (AGG), and the propensity for AGG will increase with the heat-treatment temperature. The AGG behavior will also vary with the defects in the grains. These predictions are qualitatively confirmed in the sintered WC-Co alloy prepared from fine (0.85-Μm) and coarse (5.48-Μm) WC powders and their mixtures. The observed dependence of the AGG behavior on the sintering temperature and the milling of the WC powder is also qualitatively consistent with the predicted behavior.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the friction and wear characteristics of nanocrystalline aluminum as a function of grain size, and proposed an empirical equation based on the Archard's Law to describe the effect of grain refinement on the wear resistance under unlubricated sliding conditions.
Abstract: The friction and wear characteristics of nanocrystalline aluminum were investigated as a function of grain size. Nanocrystalline aluminum samples with an average diameter of 16.4 nm were produced using an r.f. magnetron sputtering technique. The grain size was increased (up to 98.0 nm) by an isothermal annealing treatment at 573 K. Hardness measurements were performed using an ultra-microhardness indentation system and it was observed that within the grain size range of 15–100 nm the hardness-grain size data could be well represented by the Hall-Petch relationship. Friction and wear measurements were made using a miniature pin-on-disk type tribometer under unlubricated conditions both in air and in vacuum. The coefficient of friction of aluminum tested against a stainless steel pin varied with the sliding distance. At the early stages of sliding the coefficient of friction rose to a peak value, and this was followed by a decrease to a steady-state value. The transition on the friction curve corresponded to a similar transition from a severe wear regime to a mild wear above a characteristic sliding distance on the cumulative volume loss versus sliding distance curve. The value of the peak coefficient of friction decreased from μp = 1.4 for aluminum with a coarse grain size (106 nm) to μp = 0.6 for the nanocrystalline aluminum with a grain size of 16.4 nm. The coefficient of friction of nanocrystalline aluminum showed a 30% increase when tested in vacuum. In the nanocrystalline grain range, the wear rates were found to be linearly dependent on the square root of the grain size. An empirical equation based on the Archard's Law is proposed to describe the effect of grain refinement on the wear resistance under unlubricated sliding conditions. A qualitative understanding of wear processes is developed in terms of the variation of the surface morphology and subsurface strength with sliding distance.

Journal ArticleDOI
TL;DR: In this paper, the structure and properties of Co-N and Co-O based films, prepared by rf magnetron reactive sputtering using nitrogen or oxygen and argon gases, have been studied.
Abstract: The structure and properties of Co–N and Co–O based films, prepared by rf magnetron reactive sputtering using nitrogen or oxygen and argon gases, have been studied. Transmission electron microscopy (TEM) observation reveals that each Co–(Al or Si)–(N or O) film is a typical film with granular structure, with grain size less than 5 nm. It is found by micro‐focused energy‐dispersive x‐ray and electron energy loss spectroscopy analysis that the grains are mainly composed of Co and the intergranular regions are ceramics of N or O. In Co–N based films, soft magnetic properties are found in both Si and Al containing films over a wide range of film preparation conditions and compositions. Only the films with Al show soft magnetic properties in Co–O based films, which have ρ of 500–1000 μΩ cm, Hk of about 80 Oe and Bs of about 10 kG. By adding about 10 at. % Pd, the soft magnetic properties and Hk of Co–O based films are significantly improved, with Hk more than 180 Oe. These films exhibit a remarkable constant f...

Journal ArticleDOI
TL;DR: In this paper, the effects of the dopants, Mg2+, Sr2+, Sc3+, Yb3+, Gd3+, La3+, Ti4+, Zr4+, Ce4+, and Nb5+, on the grain boundary mobility of dense Y2O3 have been investigated from 1500° to 1650°C.
Abstract: The effects of the dopants, Mg2+, Sr2+, Sc3+, Yb3+, Gd3+, La3+, Ti4+, Zr4+, Ce4+, and Nb5+, on the grain boundary mobility of dense Y2O3 have been investigated from 1500° to 1650°C. Parabolic grain growth has been observed in all cases over a grain size from 0.31 to 12.5 μm. Together with atmospheric effects, the results suggest that interstitial transport is the rate-limiting step for diffusive processes in Y2O3, which is also the case in CeO2. The effect of solute drag cannot be ascertained but the anomalous effect of undersized dopants (Ti and Nb) on diffusion enhancement, previously reported in CeO2, is again confirmed. Indications of very large binding energies between aliovalent dopants and oxygen defects are also observed. Overall, the most effective grain growth inhibitor is Zr4+, while the most potent grain growth promoter is Sr2+, both at 1.0% concentration.

Journal ArticleDOI
TL;DR: In this paper, the effect of heat treatment on the grain size, phase assemblage, and mechanical properties of a 3 mol% Y-TZP ceramic was investigated.
Abstract: The effect of heat treatment on the grain size, phase assemblage, and mechanical properties of a 3 mol% Y-TZP ceramic was investigated. Specimens were initially sintered for 2 h at 1450 C to near theoretical density; some specimens were then heat-treated at 1550, 1650, 1750, or 1850 C to coarsen the microstructure. The average grain size increased with heat treatment from 1750 C. The maximum fraction of tetragonal phase that transformed during fracture corresponded with the largest tetragonal grain size of {approximately}5--6 {micro}m. Strength was on the order of 1 GPa, and was surprisingly insensitive to heat-treatment temperature and grain size, contrary to previous studies. The fracture toughness increased from 4 to 10 MPa{center_dot}m{sup 1/2} with increasing grain size, owing to an increasing transformation zone size. Grain sizes larger than 5--6 {micro}m spontaneously transformed to monoclinic phase during cooling. Such critical grain sizes are much larger than those found in past investigations, and may be due to the greater fraction of cubic phase present which decreases the strain energy arising from more » crystallographic thermal expansion anisotropy of the tetragonal phase. « less

Journal ArticleDOI
TL;DR: In this article, structural and morphological analysis of nanocrystalline SnO2 for gas sensor applications were performed at different annealing conditions by using nanopowders and thin nanocrystine layers, and the evolution of the grain size and the morphology of Pt doped tin dioxide nanoparticles with increase of annaling temperature from 450 to 1000°C were analyzed by means of transmission electron microscopy, X-ray diffraction (XRD), and Fourier transform infrared (FTIR) and micro-Raman spectroscopies.
Abstract: Structural and morphological analysis of nanocrystalline SnO2 for gas sensor applications were performed at different annealing conditions by using nanopowders and thin nanocrystalline layers. The evolution of the grain size and the morphology of Pt doped tin dioxide nanoparticles with increase of annealing temperature from 450 to 1000°C were analyzed by means of transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) and micro-Raman spectroscopies. TEM shows that the average particle size increases, the size distribution becomes more spread out, and the grain faceting, as a mechanism of energy minimization, is more evident with increasing temperature. Furthermore, the shape of the particles changes with the annealing temperature, which explains the results of the FTIR spectra using the Theory of the Average Dielectric Constant (TADC). As temperature increases, the Raman spectra are modified in agreement with a reduction of the crystalline defect concentration and a grain size increase. The the tin nanocrystalline SnO2 layers, deposited on α-Al2O3 or on thermally oxidezed Si substrates, have been annealed at 700° C for 8 h under different atmospheres, such as oxygen or synthetic air. TEM proves that the annealing atmosphere has a strong influence on the size and size distribution of the nanoparticles in the thin layer. The main differences are found near the layer-substrate interface and are dependent on the annealing atmosphere as well as the nature of the substrate.

Journal ArticleDOI
TL;DR: In this paper, various conduction models for two-phase materials are considered and the range of applicability of these models is discussed, and experimental work is carried out on construction sand of various grain size and different porosity in air at atmospheric pressure, and the results are compared with theoretical models.

Journal ArticleDOI
TL;DR: In this article, the microstructure of ball-milled iron powder has been investigated by high-resolution X-ray line profile analysis, and it has been shown that strain broadening, even in these nanoscale small-grain particles, is caused by the presence of dislocations.

Journal ArticleDOI
TL;DR: In this article, the authors measured initial magnetic susceptibility χ0 in grown and natural magnetite crystals ranging from 0.09 μm to 6 mm in grain size and found that the presented initial susceptibilities are essentially independent of grain size.

Journal ArticleDOI
TL;DR: In this article, a physically based model for predicting recrystallization microstructures and textures after hot deformation of aluminium is presented, which differs from similar models developed for steels.

Journal ArticleDOI
TL;DR: The influence of grain boundaries is limited to the near room temperature range as shown by comparison of permeation data obtained at 293 and 373 K in polycrystalline nickel samples with the electrochemical permeation technique as mentioned in this paper.

Journal ArticleDOI
S. B. Ren1, C. J. Lu1, J. S. Liu1, Huimin Shen1, Y.N. Wang1 
TL;DR: It is found that a domain-structure transition, from predominantly multidomain to predominantly single domain occurs at a grain size of ;150 nm~corresponding to a thickness 200–300 nm!.
Abstract: We studied the size dependence of the ferroelectric domain structure in unique free-standing ${\mathrm{PbTiO}}_{3}$ thin film, composed of grains 60--1000 nm in size, with transmission-electron microscopy. With such samples, we showed that the apparent dependence of electrical properties on the thickness of polycrystalline thin films stems from their grain-size dependence. We found that a domain-structure transition, from predominantly multidomain to predominantly single domain occurs at a grain size of \ensuremath{\sim}150 nm (corresponding to a thickness 200--300 nm). Based on these experimental results, the drastic change of coercive field and dielectric permittivity below a thickness 200--300 nm was reasonably explained as resulting from a domain-structure transition. \textcopyright{} 1996 The American Physical Society.

Journal ArticleDOI
TL;DR: In this article, a patterned SiO2 capping layer on top of Si films is utilized as an antireflective coating in order to induce artificially controlled super lateral growth in the film upon being irradiated with a single excimer laser pulse.
Abstract: Based on the previously elucidated super lateral growth phenomenon, we have developed an excimer‐laser‐crystallization method that produces large‐grained and grain‐boundary‐ location‐controlled Si films on SiO2 and which possesses a wide processing window. For the set of experiments reported in this letter, a patterned SiO2 capping layer on top of Si films is utilized as an anti‐reflective coating in order to induce artificially controlled super‐lateral growth in the film upon being irradiated with a single excimer laser pulse. For a simple SiO2 stripe pattern, the occlusion among the laterally and directionally solidifying grains permits the eventual development of elongated parallel grains with a single perpendicular grain boundary which is localized in the middle of the completely melted regions, provided that the width of the completely molten region is sufficiently narrow so as to avoid the nucleation of solids in the supercooled liquid.

Journal ArticleDOI
TL;DR: In this article, the influence of low energy ball milling on the crystallite size, lattice strain, and storage of deformation energies of elemental metal powders was studied, and the formation of nanosized grains (5 − 25 nm) and enhancement of lattice straining up to 0.4% was found.
Abstract: The influence of low energy ball milling on the crystallite size, lattice strain, and storage of deformation energies of elemental metal powders is studied. The formation of nanosized grains (5–25 nm) and enhancement of lattice strain up to 0.4% is found. Excess enthalpies of up to 25% of the heat of fusion are reached.

Journal ArticleDOI
TL;DR: In this paper, the role of grain size, exchange and dipolar coupling between grains is discussed in detail in the case of nanocrystalline composites, and a quantitative analysis of the numerical results for and the remanence leads to logarithmic dependences on grain size.
Abstract: High-performance magnetic materials are based on outstanding intrinsic magnetic properties and optimized microstructures and alloy compositions. The interactions between these three parameters in general are rather complex and cannot be treated explicitly by the theory of micromagnetism. Instead numerical methods have to be applied in order to determine the characteristic properties of hysteresis loops. Within the framework of computational micromagnetism (nanomagnetism) using the finite-element method the coercive fields of different types of grain ensembles have been determined. In the case of nanocrystalline composites the roles of grain size, exchange and dipolar coupling between grains will be discussed in detail. It is shown that, in sintered magnets, large coercivities require magnetic de-coupling between the grains, whereas regions with exchange coupling reduce the coercive field drastically, but, however, increase the remanence. Nanocrystalline composite materials with remanence enhancement and high coercivities are shown to require soft grains with diameters of twice the wall width of the hard magnetic phase. For an amount of 50% -Fe coercivities of , a remanence of 1.5 T and an energy product of are expected. A quantitative analysis of the numerical results for and the remanence leads to logarithmic dependences on grain size.

Journal ArticleDOI
TL;DR: In this article, the direct piezoelectric effect in fine and coarse grain barium titanate ceramics is examined as a function of the external alternating and static pressure.
Abstract: The direct piezoelectric effect in fine and coarse grain barium titanate ceramics is examined as a function of the external alternating and static pressure. It is found that domain wall vibrations contribute to the piezoelectric effect in both types of ceramics, but this contribution is smaller in the fine grain material. The external static pressure reduces domain wall contributions in the coarse grain samples and has little effect on the properties of the fine grain material. The results are consistent with the presence of a strong internal pressure in the fine grain ceramics.

Journal ArticleDOI
TL;DR: In this paper, the authors determined the stress, density and refractive index of titania films for layers deposited on fused silica substrates by reactive evaporation (RE), reactive ion plating (IP), plasma impulse chemical vapour deposition (PICVD) and spin coating (SC).