Showing papers on "Grain growth published in 1987"
TL;DR: In this paper, the effect of oxygen contamination on the densification of TiB2 ceramics, densification and grain growth behavior were examined as a function of oxygen content of the powder and compared with those observed during hot-pressing (1400° to 1700°C).
Abstract: In order to identify the mechanisms behind the adverse effect of oxygen contamination on the densification of TiB2 ceramics, densification and grain growth behavior during pressureless sintering (1700° to 2050°C) were examined as a function of oxygen content of the powder and compared with those observed during hot-pressing (1400° to 1700°C). Marked difference in the grain size-density relations was observed between the two processing methods. Specific roles of oxygen in various kinetic processes were analyzed and the likely oxygen-bearing species were also identified.
236 citations
TL;DR: In this article, it was shown that if uniform grain boundary energy is the only factor affecting boundary motion, an abnormally large grain in a matrix of normal grains does not grow at a higher relative rate than its neighbors.
184 citations
TL;DR: In this article, the authors studied how the presence of a liquid phase affects the grain morphology and grain growth kinetics in Al2O3 at 1800°C using the growth of both matrix grains and large spherical single-crystal seeds growing into the matrix.
Abstract: In this investigation we have studied how the presence of a liquid phase affects the grain morphology and grain growth kinetics in Al2O3 at 1800°C using the growth of both matrix grains and large spherical single-crystal seeds growing into the matrix. The growth rates of the matrix grains were found to decrease in the following order: undoped Al2O3, AI2O3 with anorthite, AI2O3 with anorthite and MgO, and Al2O3 with MgO. Except for the samples doped with MgO alone, the matrix grains were faceted and appeared tabular in polished sections. In samples containing anorthite both with and without MgO, the single-crystal seeds exhibit basal facets with continuous liquid films and slow growth in the 〈0001〉 relative to all other crystallographic directions. When only MgO is added, the growth of the single-crystal seeds was not isotropic; however, no faceting was observed. We discuss how anisotropic growth rates caused by the anorthite additions can stimulate discontinuous grain growth in Al2O3.
181 citations
TL;DR: In this paper, complex impedance measurements and detailed analysis of the grain-boundary microstructure have been made on fully stabilized yttria-zirconia sintered bodies as a function of grain size.
Abstract: Complex impedance measurements and detailed analysis of the grain-boundary microstructure have been made on fully stabilized yttria-zirconia sintered bodies as a function of grain size. The prereacted yttria-zirconia powder used in this study was obtained from a commercial source. The powder has very high reactivity and starts sintering around 1200° C. The densification process is complete around 1350° C but the grain growth continues almost linearly with sintering temperature. The grain size variation obtained was between 1 and 30 μm. The grain-boundary resistivity when plotted against grain size showed an inflection in the vicinity of 1500° C sintering temperature. These results have been explained in terms of the grain-boundary microstructure changing with the sintering temperature. The thickness of the grain-boundary layer determined from impedance data and transmission electron micrographs are in reasonably good agreement. The activation energy for the grain-boundary resistivity was only slightly higher than that for the lattice resistivity.
177 citations
TL;DR: In this paper, several grain-scale microstructures are presented that are thought to demonstrate the migration direction of once-mobile grain boundaries in a naturally deformed quartzite, and an analysis of the sense of migration of the boundaries, and the characteristics of the patterns of relative grain growth and shrinkage.
149 citations
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TL;DR: In this paper, a new model was presented to predict the critical grain radius (Rc) as a function of the particle radius (r) and of the volume fraction of the particles (ƒ), which was found to agree satisfactorily with the experimental results of Tweed, Hansen and Ralph.
146 citations
TL;DR: In this paper, normal and secondary grain growth in thin films of germanium on silicon dioxide was observed and characterized, and the grain size distributions were lognormal with mean grain diameters of about 2.5 times the film thickness.
Abstract: We have observed and characterized normal and secondary grain growth in thin films of germanium on silicon dioxide. Films were deposited on thermally oxidized silicon wafers, encapsulated with 1000‐A‐thick sputtered SiO2 films and annealed in evacuated ampoules at 900 and 915 °C. After 5 min, the films had developed a columnar grain structure as a result of normal grain growth. The grain size distributions were lognormal with mean grain diameters of about 2.5 times the film thickness. The standard deviation of the normal grain size distribution did not change significantly with annealing time and temperature. Secondary grain growth, which can lead to grains that are much larger than the film thickness, occurred in films that were annealed for longer periods of time. The normal grain size distribution remained stationary, i.e., the peak height and width did not increase with annealing time. Secondary grains were few in number compared to normal grains, and were manifest as a small tail on the normal grain size distribution. The rate of secondary grain growth was constant and largest in the thinnest films.
143 citations
TL;DR: In this article, the authors investigated grain growth habits and the structure of grain boundaries using transmission electron microscopy and scanning Auger microscopy of bulk sintered samples of orthorhombic Ba 2 YCu 3 O 7-x, and proposed a model based on the highly anisotropic thermal contraction of the material during cooling from the high sintering temperatures.
128 citations
TL;DR: In this paper, the geometry and topology of two-dimensional grain structures have been analyzed for different conditions of nucleation and growth to impingement, including simultaneous nucleation at a fixed number of sites, and continuous nucleation per unit of untransformed area.
127 citations
TL;DR: In this article, a theory of isothermal grain growth in polycrystalline solids, which treats grain growth as a statistical or stochastic process, is presented, where the noise or fluctuations are used to model the effect of complex topologically connected structure of the specimen on grain boundary motion, in addition to such motion directed by surface tension forces.
115 citations
TL;DR: In this paper, the authors used network simulation techniques to calculate the electrical conductivity of the ordered versions of the grain consolidation model and found that the minimum area approximation employed in their earlier work is generally quite satisfactory.
Abstract: In the grain consolidation model the diagenetic processes of compaction and cementation are represented in terms of the growth of an array of originally spherical grains. Grain growth toward the nodes of the pore space leads to an electrical formation factor F(ϕ) that increases slowly as the porosity ϕ decreases. By contrast, grain growth toward the throats of the pore space leads to a rapidly increasing F(ϕ). In all the cases we have examined, the value of the percolation threshold, ϕc is less than 0.055. Network simulation techniques have been developed to calculate the electrical conductivity of the ordered versions of the grain consolidation model. We find that the minimum‐area approximation employed in our earlier work is generally quite satisfactory. The network techniques can also be used to model the effects of mixed pore‐space fluid saturation, with results that are physically reasonable although not necessarily in agreement with empirical rules regarding saturation.
TL;DR: In this paper, an analytical model that accounts for the different variation of the limiting grain radius with volume fraction of particles found in previous computer simulations as compared to the classic Zener predictions is presented.
TL;DR: In this article, the effect of Al2O3 inclusions with a greater average size (0.6 μm) than the average particle size of the major phase powder (0,3,5,10, and 20 vol%) on grain gowth was examined by sintering ZrO2/Al 2O3 composites at 1400°C and then heat treating at temperatures up to 1700°C.
Abstract: The effect of Al2O3 inclusions with a greater average size (0.6 μm) than the average particle size of the major phase powder (<0.1 μm) on grain gowth was examined by sintering ZrO2/Al2O3 composites (0,3,5,10, and 20 vol%) at 1400°C and then heat-treating at temperatures up to 1700°C. Normal grain growth was observed for all conditions. The inclusions appeared to have no effect on grain growth until the ZrO2 grain size was ∼1.5 times the average inclusion size. Grain growth inhibition increased with volume fraction of the Al2O3 inclusion phase. At temperatures 1600°C, the inclusions were relatively immobile and most were located within the ZrO2 grains for volume fractions <0.20; at higher temperatures, the inclusions could move with the grain boundary to coalesce. Grain growth was less inhilited when the inclusions could move with the boundaries, resulting in a larger increase in grain size than observed at lower temperatures. Analogies between mobile voids, entrapped within grain at lower temperature due to abnormal grain growth during the last state of sintering, and the observations concerning the mobile inclusions are made suggesting that grain-boundary movement can “sweep” voids to grain boundaries and eventually of four-grain junctions, where they are more likely to disappear by mass transport.
TL;DR: In this paper, the sintering pressure of polycrystalline polycrystals was analyzed by coupling the change in interface energies and the total volume of the polycrystal, and it was discovered that the sinting pressure is a sum of two terms, one deriving from the surface curvature of the pores and the other depending on the size of the grains.
Abstract: When the sintering of a polycrystalline body is analyzed by coupling the change in interface energies and the change in total volume of the polycrystal, it is discovered that the sintering pressure is a sum of two terms, one deriving from the surface curvature of the pores and the other depending on the size of the grains. When pores are present at two-grain, three-grain, or four-grain junctions, and when the number of pores of each type per particle remains constant, the sintering pressure is expressed by a simple equation. This result may suggest new approaches to the problem of grain growth during the sintering process. The result also highlights a fundamental difference between the sintering of ceramics and the sintering of glasses.
TL;DR: In this article, the authors obtained ultrafine grained Al 2 O 3, TiO 2 and ZrO 2 based ceramics by hot-pressing powders to full density.
TL;DR: In this paper, the grain growth of donor-doped BaTiO3 at different oxygen partial pressures was studied, and it was shown that the oxygen pressure had a pronounced influence on grain growth and related effects.
Abstract: The grain growth of donor-doped BaTiO3 at different oxygen partial pressures was studied. Results showed that the oxygen pressure had a pronounced influence on the grain growth and related effects. A model for the grain size anomaly during sintering of donor-doped BaTiO3 in the presence of a TiO2-rich liquid phase is proposed.
TL;DR: On formule le processus de nucleation homogene et de croissance de grains for un mineral satisfaisant la relation stœchiometrique. as discussed by the authors, a.p.
Abstract: On formule le processus de nucleation homogene et de croissance de grains pour un mineral satisfaisant la relation stœchiometrique. Application a la condensation de mineraux refractaires dans un gaz refroidi de composition solaire. Discussion de formations de grains dans l'environnement astrophysique
TL;DR: Si 3 N 4 composite materials containing up to 60 vol.% of dispersed β-SiC particles were sintered with Y 2 O 3 and Al O 3 at 1850°C and 0·1 MPa N 2.
TL;DR: In contrast to the voluminous literature devoted to the structure of grain boundaries in metals and, to a lesser extent, in diamond cubic semiconformal ductors, relatively few studies have been directed to elucidating the struc · ture of grain boundary in ceramic materials.
Abstract: In contrast to the voluminous literature devoted to the structure of grain boundaries in metals and, to a lesser extent, in diamond cubic semicon ductors, relatively few studies have been directed to elucidating the struc ture of grain boundaries in ceramic materials. The crystallographic studies performed have been reviewed by Balluffi and colleagues (1, 2), but these papers, reflecting the work carried out to date, have been restricted to single-phase ceramics of relatively simple crystal structures and small unit cells. Much less attention has been given to the more complicated polyphase ceramics that are of importance to ceramic scientists today. These include the structural ceramics, such as the silicon nitride alloys (3, 4) and the zirconia transformation toughened materials (5); the multicomponent sub strate ceramics; nuclear waste ceramics (6); and the dielectric and electrical ceramics. In all these materials the majority of grain boundaries have been found (7-14) to be coated with a very thin ( 1-10 nm) film of a (generally siliceous) glass. I [In many respects the microstructure of the boundaries in these materials can be likened to the microstructure envisioned in the liquid-layer grain boundary model for metals which was introduced by Rosenhain (15) and was current during the early decades of this century.] The presence of such a glass phase can have a profound eflect on the properties of such polyphase ceramics. For instance, the unique electrical properties of a number of electrical ceramics, such as the barrier-layer
TL;DR: Ion irradiation induced grain growth in Pd polycrystalline thin films was studied by transmission electron microscopy for 100−keV Ne+, 185-keV Ar+, and 560 −keV Xe++ irradiations over a wide range of doses as discussed by the authors.
Abstract: Ion irradiation induced grain growth in Pd polycrystalline thin films was studied by transmission electron microscopy for 100‐keV Ne+, 185‐keV Ar+, and 560‐keV Xe++ irradiations over a wide range of doses Grain growth from 9 to 60 nm was observed after ion irradiations Initially, the amount of growth is approximately linear with the irradiation dose; the growth saturates in the high dose region The saturated grain size scales with the dimension of the individual collision cascade and increases with the mass of the irradiating ion In the proposed physical picture of ion irradiation induced grain growth, a heavily damaged region created by an individual collision cascade is surrounded by relatively undamaged grains The growth of those surrounding grains into the heavily damaged region leads to the grain growth in the irradiated Pd film
TL;DR: The use of ultra-high-purity powder processing and multiple solid-solution additive doping has been evaluated as an effective approach for the fabrication of alumina ceramics as discussed by the authors.
Abstract: The use of ultra-high-purity powder processing and multiple solid-solution additive doping has been evaluated as an effective approach for the fabrication of alumina ceramics. MgO was found to inhibit grain growth more strongly in very pure powders because of its stronger solute drag effect. The degree of inhibition was severe enough to render grain growth insensitive to porosity. By diminishing the dragging influence of pores on grain-boundary motion, MgO guards against abnormal grain growth due to inhomogeneous densification. FeO acted singly in alumina to promote grain growth more than densification. FeO was not, therefore, an effective sintering additive for undoped alumina. FeO did, however, Ceramic benefit the sintering of MgO-doped alumina.
TL;DR: In this article, the intrinsic stress of AIN, prepared by dual-ion-beam sputtering, has been investigated as a function of deposition temperature and nitrogen ion energy, and the results show that the stress is compressive over the temperature range 75-700°C with a maximum value of -28×10 9 dyn cm -2 at 75°C.
01 Jan 1987-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this paper, a homogeneous grain growth from 9 to 40 run was observed after irradiations. But the absence of inhibition of grain growth for the irradiated samples leads to homogenous grain growth.
Abstract: Ion irradiation induced grain growth in Ni polycrystalline thin films has been studied by transmission electron microscopy. At room temperature, irradiations were carried out with 240 keV Ar, 150–580 keV Kr and 560 keV Xe ions over a wide range of doses. A homogeneous grain growth from 9 to 40 run was observed after irradiations. Initially, the dimension of grains increases with the irradiation dose and the growth saturates in the high dose region. The dimension of a damaged volume generated by a single collision cascade determines the growth rate and the saturated grain size. Elevated temperature irradiations and annealing were performed to compare different mechanisms of grain growth. Samples irradiated with 1015 Kr/cm2 at 200°C show uniformly enlarged grains, comparing to the non-uniform grain growth on the thermally annealed samples. The absence of inhibition of grain growth for the irradiated samples leads to homogeneous grain growth.
TL;DR: In this article, the microstructures and mechanical properties of Al-1%Si thin film metallizations annealed at temperatures ranging from 250 to 500 °C and then chemically removed from their substrates were evaluated at room temperature.
TL;DR: In this article, a stochastic theory of normal grain growth is proposed, based on the concept that the migration of kinks and ledges should cause a Brownian motion of the grain boundary.
TL;DR: In this article, a technique combining photolithographic methods, ion beam etching, and hot-pressing has been developed, which permits the generation of a wide range of controlled pore structures.
Abstract: A technique, combining photolithographic methods, ion beam etching, and hot-pressing, has been developed, which permits the generation of a wide range of controlled pore structures. Pores in almost any number, and of almost any size and spacing, can be produced at grain boundaries with controlled misohentation. This new method has permitted the development of novel experiments, which are being used to study pore-drag effects during grain growth, pore morphology evolution during crack healing, faceting behavior, interfacial energies, and Ostwald ripening of pores.
TL;DR: In this article, the effect of dopants on the microstructure and lattice parameters of Pb0.94Sr0.06(Zr 0.53Ti0.47)O3 ceramics was studied.
Abstract: The effect of dopants on the microstructure and lattice parameters of Pb0.94Sr0.06(Zr0.53Ti0.47)O3 ceramics was studied. Small amounts (0 to 0.3 wt%) of Cr2O3, MnO2, Co2O3 and U3O8, were used as dopants. In a few compositions two oxides were used, namely U3O8 with Cr2O3 as well as MnO2 with Cr2O3 X-ray diffraction investigation of powdered samples showed that all the compositions (both modified and unmodified) were of perovskite type with tetragonal symmetry. The Curie temperature was decreased with the decrease of tetragonal distortion indicated by the axial ratio,c0/a0, in all cases. The average grain sizes for the doped and undoped compositions were determined from SEM photomicrographs of polished and acid-etched surfaces using the linear intercept technique. The average grain size for the undoped composition was found to be 10.7μm. The addition of a small amount of dopants controlled the grain growth to give rise to the average grain size of 6.4 to 9.5μm, which appeared to have some effect on the improvement of the piezoelectric properties of the ceramics.
TL;DR: In this article, an additive effect on the pressureless sintering of boron carbide is investigated and some additive species, such as Al, TiB2, and AlF3, show a remarkable densification effect upon B4C.
Abstract: An additive effect on the pressureless sintering of boron carbide is investigated. Some additive species, Al, TiB2, and AlF3 show a remarkable densification effect upon B4C. The Al-addition provides the best sintered body with the highest bulk density of 95% by means of the firing condition of 2200°C for 30min under Argon flow. An addition of SiC prevents the densification process. The additive species except for SiC tend to restrain the grain growth and the pore growth, acting probably as an inhibitor for the surface matter transport.
Patent•
09 Jan 1987
TL;DR: The polycrystalline tungsten carbide ceramic can be formed into wear components having improved performance in comparison to cemented TCL in a variety of drilling, cutting, milling, and other wear applications.
Abstract: A tungsten carbide ceramic material which cuts titanium alloys four to five times faster than cemented carbide, ceramic-coated cemented carbides or state-of-the-art ceramic cutting tools can be densified with or without applied pressure at temperatures below 1700oC. Grain growth inhibitors or sintering aids can be added to control grain size in the final product. The polycrystalline tungsten carbide ceramic can be formed into wear components having improved performance in comparison to cemented tungsten carbides in a variety of drilling, cutting, milling, and other wear applications.