Showing papers on "Grain growth published in 1969"
TL;DR: In this article, the average grain size of a log-normal distribution of grain sizes with tetrakaidecahedral shape is related to the average intercept size by a proportionality constant.
Abstract: A model is proposed which realistically characterizes the grain structure of polycrystalline ceramics. The average grain size of a log-normal distribution of grain sizes with tetrakaidecahedral (truncated octahedral) shape is related to the average intercept size by a proportionality constant. This result can be used to determine the average grain size of a sintered powder compact composed of nontextured grains which shows no discontinuous grain growth.
1,732 citations
323 citations
TL;DR: In this paper, the authors investigated the effects of small additions of Fe2O3 to lead zirconate-lead titanate ceramics with compositions between 45 and 60 mol% lead ZIRconate and showed that the dielectric constant and dissipation factor for both rhombohedra1 and tetragonal materials were decreased by addition of iron oxide.
Abstract: An investigation of the effects of small additions of Fe2O3 to lead zirconate-lead titanate ceramics with compositions between 45 and 60 mol% lead zirconate has shown that, with 2 moles of PbO to balance each mole of Fe2O3, the solubility of Fe2O3 was about 0.8 wt% in compositions near the tetragonal-rhombohedra1 boundary. The dielectric constant and dissipation factor for both rhombohedra1 and tetragonal materials were decreased by addition of iron oxide, whereas the mechanical quality factor and frequency constant were increased. The dependence of the electromechanical properties on grain size was qualitatively similar for both undoped and iron oxide-doped materials; the presence of iron oxide inhibited grain growth and lowered the limiting grain size below which the electromechanical properties change rapidly with grain size.
121 citations
TL;DR: In this article, it was shown that sulfur is strongly segregated to grain boundaries in nickel alloys and this segregation causes a local increase in microhardness and an unusual variation of the Petch slope k in the grain size dependence of the flow stress.
92 citations
TL;DR: In this article, the correlation between the mechanism of recrystallisation and the annealing texture of aluminium-copper alloys was investigated by transmission electron microscopy and selected area diffraction, and pole figure determination by X-rays.
Abstract: The correlation between the mechanism of recrystallisation and the annealing texture of aluminium-copper alloys was investigated by transmission electron microscopy and selected area diffraction, and pole figure determination by X-rays. Continuous recrystallisation by sub-grain growth leads to preservation of the rolling texture, while recrystallisation by motion of a high-angle boundary produces a cube texture as in pure aluminium. The conditions under which the different modes of recrystallisation occur and the reasons for the formation of the two types of textures are discussed on the basis of microscopic mechanisms.
68 citations
TL;DR: In this paper, the effect of particle size on the sintering kinetics of AIN powder was investigated in the temperature range from 1600 to 2000°C and the results were analyzed on the basis of vacancy diffusion models.
Abstract: The effect of particle size (0.78 ∼ 4.4 μm) on the sintering kinetics of AIN powder was investigated in the temperature range from 1600 to 2000° C and the results were analysed on the basis of vacancy diffusion models. The mechanisms of sintering are discussed. Fractional shrinkage is proportional to the nth power of soaking time with n = 0.20 for 4.4 μm and 1.5 μm powders and 0.33 for 0.78 μm powder. For the 0.78 μm powder at 1900° C, however, n decreases gradually as grain growth proceeds. The experimental activation energy for sintering is between 92 kcal/mole for 4.4 μm and 129 kcal/mole for 0.78 μm powder. Unlike this activated energy, the rate of sintering and the diffusion constant calculated from it increase drastically with decrease of particle size; the derived diffusion constant for 1.5 μm powder is 101 to 102 times larger than that of 4.4 μm powder, and for 0.78 μm powder the diffusion constant is estimated to be still higher. The particle-size dependence of parameter n and the diffusion constant seems to be caused by a variation in predominant diffusion mechanisms; namely, bulk diffusion in coarse powder and surface or grain-boundary diffusion in fine powder.
50 citations
46 citations
TL;DR: In this article, the microstructural changes which occur during the liquid-phase sintering of the alloys NbC-22 wt.% Fe and Ni-Ni alloy were investigated and the effect of temperature on grain growth was measured and activation energies of the growth rates were determined.
Abstract: An investigation has been made of the microstructural changes which occur during the liquid-phase sintering of the alloys NbC-22 wt.% Fe andNbC-22 wt.% Ni. It was found that the growth of the carbide grains, dispersed in either of the liquid metals, is consistent with the theoretical equation, derived by Wagner, for a solution/ precipitation growth process controlled by the diffusion of the solid constituent through the liquid. The same growth behaviour has been observed earlier in a similar alloy of NbC in cobalt. The effect of temperature on grain growth was measured and “activation energies” of the growth rates were determined.
43 citations
TL;DR: In this paper, the microstructure of pure polycrystalline nickel foil after explosive-shock loading and subsequent heat treatments between 600° and 780°C was made by transmission electron microscopy.
Abstract: A study by transmission electron microscopy was made of the microstructure of pure polycrystalline nickel foil after explosive‐shock loading and subsequent heat treatments between 600° and 780°C. In the instance of specimens shocked at 70 and 320 kbar, the deformation substructures resemble those normally caused by cold work, but the recovery process consists mainly in dislocation migration and recombination; no polygonization, nucleation, or grain growth are observed. Nickel shocked at 1000 kbar on the other hand, exhibits an extremely high density of dislocations, point defect clusters, and microtwins arranged in complex patterns. In this instance, heat treatment causes nonuniform polygonization, nucleation, and grain‐boundary migration. This results in a significantly lower dislocation density after annealing, particularly at the higher temperatures, and considerably more extensive softening than is the case for nickel shocked at lower pressures.
41 citations
TL;DR: In this article, a grain-oriented silicon iron with high permeability was prepared using aluminum-nitride needles to restrain normal grain growth, and the improvements in hysteresis loss of specimens with a permeability of 1920 were about 0.120 W/kg at 15 kG and 0.160 W/ kg at 17 kG.
Abstract: Grain‐oriented silicon iron with high permeability is prepared using aluminum‐nitride needles to restrain normal grain growth. The improvements in hysteresis loss of specimens with a permeability of 1920 are about 0.120 W/kg at 15 kG and 0.160 W/kg at 17 kG as compared to the commerical product with a permeability of 1820. That is the reason why the crystal orientation has a strong influence on total loss, especially at B = 17 kG. The effect of grain size on total loss is important also. The detrimental aluminum nitride and aluminum oxide are not present in the base metal after final annealing. For example, aluminum oxide is removed from the base metal and absorbed into a glass film. Glass‐type coating plays a dominant role, not only for the magnetostriction, but also for total loss of these specimens with high permeability, especially in thin‐gauge specimens.
34 citations
TL;DR: In this article, UO2-stainless steel fuel pins were irradiated in DIDO to 0.8-5.0% burn-up, and a large increase in gas release occurred in both diffusional and non-diffusional regimes.
TL;DR: In this article, the effects of solute segregation and boundary structures on grain boundary motion and grain growth, boundary energy studies, field ion microscope observations, and nonequilibrium impurity segregation at boundaries are discussed.
TL;DR: In this article, the authors studied the kinetics of secondary grain growth in a Ti02-nucleated β-spodumene solid-solution glass-ceramic and found that grain growth followed the cube-root-of-time law.
Abstract: The kinetics of secondary grain growth in a Ti02-nucleated β-spodumene solid-solution glass-ceramic was studied. The thermal stability of the grains was excellent. Grain growth followed the cube-root-of-time law. The activation energy of the grain boundary migration was 55 ± 10 kcal/mol. Grain growth inhibition due to Ti02 precipitates and the residual glassy phase was closely examined. The excellent thermal stability of the grains is due to grain growth inhibition by the residual glassy phase, not by rutile precipitates. It is suggested that the diffusion of A2+, and probably the simultaneous diffusion of Li+, through the residual glass is the rate-limiting process for the grain boundary migration.
TL;DR: In this article, grain growth curves for AISI Type 304, 316, and 321 were obtained and compared and grain growth characteristics were established at temperatures between 1900°F and 2300°F, for periods of 5, 15, and 60 minutes.
TL;DR: In this paper, it is suggested that the grain growth in this case is assisted by thermal stresses which are set up as a result of local heating, and are thus different from those resulting from direct annealing treatment.
TL;DR: In this paper, a polycrystalline ZnO has been hot-pressed to theoretical density at 5000 psi and 800°C, with an average grain size of 1.5 microns.
TL;DR: In this article, the two commonly used relations to describe isothermal grain growth in materials (dD/dt=KjDm and D = βtn, where D is the grain size, t growth time, and K, β, m and n are constants defined in the text) are considered and the correct grain growth equations consistent with the boundary conditions are derived.
Abstract: The two commonly used relations to describe isothermal grain growth in materials (dD/dt=KjDm and D = βtn , where D is the grain size, t growth time, and K, β, m and n are constants defined in the text) are considered and the correct grain growth equations consistent with the boundary conditions are derived. The criteria under which these equations can be simplified and the errors that would result when these criteria are violated are discussed. The relation between the parameters used in the two equations is derived and it is shown that the criteria under which the two equations can be simplified are the same in both cases. A graphical method of finding the solutions is given.
TL;DR: In this article, the authors present observed metallographic structures of the various binary and ternary lead alloys, cast under air or inert atmosphere and with controlled solidification rates.
TL;DR: In this article, the effects of grain size on the switching properties of lithium ferrite and to establish the best grain size for a fast switching speed, with a minimum increase of coercive force were determined.
Abstract: This study was to determine the effects of grain size on the switching properties of lithium ferrite and to establish the best grain size for a fast switching speed, with a minimum increase of coercive force. Lithium ferrite (Li0.5Fe2.5O4) powder prepared by four preparation techniques; flame spraying, commercial techniques, fluid‐bed reaction, and Li2CO3+Fe2O3 mixture, was densified by hot pressing or conventional sintering. There was a variation in the grain growth and densification characteristics of the powders, but the magnetic properties were similar for a given grain size. The magnetic properties which were evaluated as a function of grain size were squareness, switching coefficient, coercive force, and switching time. These properties were evaluated for a 0.7 to 15.0 μ grain‐size range in order to establish the effects of grain size on switching speed and coercive force. It is shown that samples with a reduced grain size have twice the switching speed of larger grain‐size samples with little or no...
TL;DR: In this paper, a method for obtaining fine-grain, non-columnar tungsten (W) by chemical vapor deposition (CVD) is described, which involves the partial nitriding of the tengsten to W 2 n during deposition, and subsequent decomposition of the W 2 N.
Abstract: A method is described of obtaining fine-grain, non-columnar tungsten (W) by chemical vapor deposition (CVD). Typical CVD tungsten grows columnar grains perpendicular to a heated surface when deposited from its halides, generally WF or WCl 6 . The present method involves the partial nitriding of the tungsten to W 2 N. during deposition, and subsequent decomposition of the W 2 N. The presence of this second phase (W 2 N) alters the growth pattern of the depositing tungsten and eliminates columnar grain growth.
TL;DR: In this paper, it was shown that sulfur and nitrogen, when present together as solutes, will enable secondary recrystallization to occur in silicon-iron, which is attributed to dispersions of small inclusions usually identified as sulfides or nitrides.
Abstract: The secondary recrystallization of silicon‐iron requires that normal grain growth be restrained. This restraint has been attributed to dispersions of small inclusions usually identified as sulfides or nitrides. In this paper, it is shown that sulfur and nitrogen, when present together as solutes, will enable secondary recrystallization to occur.
TL;DR: Germanium and Mg3Sb2 were vapor codeposited on a low-temperature substrate and the resulting films were amorphous as mentioned in this paper, indicating that the annealing behavior above the transition temperature interval is associated with extensive grain growth, though below it no structure is observable at all.
Abstract: Germanium and Mg3Sb2 were vapor codeposited on a low‐temperature substrate. The resulting films were amorphous. Subsequent heating to temperatures above room temperature resulted in an ultrafine‐grained structure. Conductance measurements, used to follow the annealing process, indicated two distinct annealing modes. At low temperatures, the conductance decreased on annealing. Somewhat above room temperature, a sudden, almost discontinuous, increase in conductance occurred over a very narrow transition temperature interval. Annealing above this temperature resulted in a gradual increase in conductance. Electron microscope studies indicate that the annealing behavior above the transition temperature interval is associated with extensive grain growth, though below it no structure is observable at all. A study of the annealing behavior below the transition temperature interval by means of conduction measurements indicates an activation energy, for what must be a structural change, of about 0.1 eV. An ordinary...
TL;DR: In this article, a volume diffusion model is used taking into account the geometrical parameters of the average crystal in thermodynamical equilibrium in the polycrystalline material to compute the activation energies Q and Q 1 responsible for grain growth and for densification.
Abstract: In order to prepare reproducibly high permeability manganese-zinc ferrites, it is necessary to carefully control the sintering schedule for obtaining both a homogeneous chemical composition and the desired microstructure. The latter should consist of big pore-free crystals, the remaining porosity being a few number of big pores situated at the grain boundaries. In our theoretical analysis of the densification, a volume diffusion model is used taking into account the geometrical parameters of the average crystal in thermodynamical equilibrium in the polycrystalline material. In the intermediate stage of sintering, the grain growth and densification are correlated, the densification rate being approximately inversely proportional to the grain volume. Sintering experiments have been carried out under various conditions of temperature and duration, the atmosphere composition being adjusted for maintaining the same stoichiometry. These results permit one to define isoporosity curves. It is then possible to compute the activation energies Q and Q 1 responsible for grain growth and for densification. The values found are Q = 82 \pm 5 kcal/mole and Q_{1} = 85 \pm 5 kcal/mole, in agreement with the previous measurements of Paulus [5] and Ogawa [3]. The experimental results show that both processes are controlled by the diffusion energy of oxygen anions which are the slowest diffusing species. The variation of the porosity versus time follows a (t)^{-n} law, n being roughly equal to 0.5 in good agreement with our predicted model. The experimental results also confirm that the use of a more oxidizing atmosphere increases the grain growth rate but decreases the densification rate. A sintering schedule leading to very high permeability ferrites is determined taking into account these results. The microstructure is obtained during a first soak at high temperature under oxidizing atmosphere. This leads to big crystals and open porosity while preventing zinc losses. This first treatment is followed by a second soak under a more reducing atmosphere leading to a high density ferrite and an homogeneous chemical composition possessing a ferrous iron content so as to obtain a maximum permeability at room temperature.
TL;DR: In this article, the effect of neutron irradiation on the mechanical properties and grain growth of pure copper, Cu + 2 at % Al and Cu + 1 at % Mg in the temperature range 25-900 °C was studied and a linear relationship between the drop in ductilities and the thermal neutron integrated doses was found.
TL;DR: In this paper, the authors investigated the thermal decomposition of aluminum sulfate into α-alumina and found that the transition initiated from a part of a skeleton particle with a rapid rate.
Abstract: Thermal decomposition of aluminum sulfate into α-alumina was investigated by D. T. A., T. G. A., X-ray analysis and electron microscopic observation.The results obtained were as follow:Aluminum sulfate melted in its own water of crystallization when heated, and high viscous solution was obtained. This solution evaporated vigorously above 100°C. Bubble formation was observed because of difficulty in releasing water vapor due to high viscosity of the solution. Then the skeleton particles composed of the network of thin film layers were formed. They were decomposed to r-alumina keeping this shape. The r-alumina consisted of very fine particles. A remarkable grain growth was observed together with transition to α-form. The transition initiated from a part of a skeleton particle with a rapid rate. From this fact, the rate controlling process may be the nucleation.It was confirmed by the electron diffraction that the inside of the skeleton particle showed a high orientation because the transition and grain growth proceeded from one or a few nuclei.
TL;DR: In this article, surface characterization studies were performed on chemically vapor deposited (CVD) tungsten and the results were characterized by Auger analysis, X-ray diffraction analysis, etch pit analysis, and low energy electron diffraction (LEED) analysis.
Abstract: Surface characterization studies were performed on chemically vapor deposited (CVD) tungsten. Two specimens of tungsten were taken from each of three sample lots and prepared with standard cleaning and firing procedures and then electropolished. In order to evaluate the effect of grain size, one set of specimens was given an additional vacuum firing at 2500°C to promote grain growth. Surfaces of tungsten were characterized by Auger analysis, X-ray diffraction analysis, etch pit analysis, and low energy electron diffraction (LEED) analysis. A description of the various methods along with the results are presented.
TL;DR: In this article, the observed changes in the rate constants of grain growth and in the energy of activation for collective recrystallization are related to changes in electronic structures of the carbides in their homogeneity regions.
Abstract: During the sintering of loosely poured niobium and titanium carbide powders in their homogeneity regions at temperatures above 1600°C, collective recrystallization takes place. The observed changes in the rate constants of grain growth and in the energy of activation for collective recrystallization are related to changes in the electronic structures of the carbides in their homogeneity regions.