Showing papers on "Grain size published in 1978"
TL;DR: In this article, a stress-induced phase transformation in the metastable tetragonal phase of polycrystalline zirconia was shown to increase the strength and grain size.
Abstract: Polycrystalline zirconia containing a high content of metastable tetragonal phase shows high strength (∼ 700 MPa), high fracture toughness (Kc = 6 to 9 MN m−3/2) and small grain size (<0.3jμm). The strength and grain size remain nearly constant over a wide range of tetragonal phase content (100 to 30%). At a low concentration of tetragonal phase <30%, there is a rapid decrease in strength accompanied by a rapid increase in grain size. These results are explained by means of a stress-induced phase transformation in the metastable tetragonal phase.
438 citations
TL;DR: Grain size-microcracking trends in the three pseudobrookite oxides MgTi2O5, Fe2TiO5 and Al2 TiO5 were examined in this paper.
Abstract: Grain size-microcracking trends are examined in the three pseudobrookite oxides MgTi2O5, Fe2TiO5, and Al2TiO5. These trends are toward smaller critical grain sizes, lower elastic moduli, and lower strengths with increased thermal expansion anisotropy. Extension of an energy criterion relates the micro-cracking transition to the inverse square of the maximum difference in single-crystal thermal expansion coefficients, Δαmax-2.
241 citations
TL;DR: In this article, a 3.4mm-thick polycrystalline silicon was implanted with B to a dose of 5×1014/cm2 and irradiated in a cw laser scanning apparatus.
Abstract: 0.4‐μm‐thick polycrystalline silicon deposited in a low‐pressure CVD reactor was implanted with B to a dose of 5×1014/cm2 and then irradiated in a cw laser scanning apparatus. The laser annealing produced an increase in grain size from ∼500 A to long narrow crystals of the order of ∼25×2 μ, as observed by TEM. Each grain was found to be defect free and extended all the way to the underlying Si3N4. Electrical measurements show 100% doping activity with a Hall mobility of about 45 cm2/V sec, which is close to single‐crystal mobility at the same carrier concentration. Thermal annealing produces material with an average grain size of 1000 A and a resistivity higher by a factor of 2.2 than that obtained with the laser anneal. Laser annealing performed after a thermal anneal reduces the resistivity to approximately the same value obtained by laser annealing only.
210 citations
TL;DR: In this paper, a new model is proposed in which grainboundary sliding (GBS) in a group of grains is accommodated by a grain emerging from the next layer of grains, giving the correct increase in surface area.
Abstract: Current models for obtaining large superplastic flow without change of grain size are two-dimensional; they therefore involve rearrangement of grains without increasing the surface area of the specimen as it deforms. A new model is proposed in which grainboundary sliding (GBS) in a group of grains is accommodated by a grain emerging from the next layer of grains, giving the correct increase in surface area. This also produces curved grain boundaries and there is some rotation of grains involving plastic flow in a zone along grain boundaries (the “mantle”) of predictable width. Grains do not have to be uniform and regular for the process. Characteristic configurations of marker lines are produced by the deformation. All these features are shown to have been observed in the literature. The model does not predict a threshold stress. It can be linked with a previous constitutive equation based on the climb and glide of dislocations in the grain mantles.
157 citations
01 Jan 1978
TL;DR: The grain size distribution of six Luna 24 samples has been determined by a bimodal distribution which is indicative of soils formed primarily by mixing rather than by reworking as discussed by the authors.
Abstract: The grain size distribution of six Luna 24 samples has been determined. These samples are characterized by a bimodal distribution which is indicative of soils formed primarily by mixing rather than by reworking. Although agglutinate content decreases with depth, it is not likely that the Luna 24 soils have undergone appreciable in situ reworking. Particle types and abundances in each of four size fractions have been determined petrographically. Mineral fragments are very abundant in all analyzed size fractions. Pyroxene and plagioclase increase slightly in abundance at finer grain sizes, but olivine decreases significantly. Compared with typical mare soils, the Luna 24 trends are anomalous. They are compatible with the hypothesis than many, if not most, of the mineral grains in the 20-250-micron fractions come from coarse-grain rocks having average mineral grain sizes greater than 250 microns. The mineralogy and chemistry of the coarse-grained rocks has not been well characterized, but there is evidence that at least some of them are higher in MgO than the analyzed finer-grained basalts.
145 citations
TL;DR: In situ measurements were carried out of stress at the AlSiO2 interface at various temperatures (25-500 °C) and for various film thicknesses (0.2-1.6 microm) as mentioned in this paper.
116 citations
TL;DR: In this paper, the variation of electrical resistivity of an insulator-conductor composite, namely, waxgraphite composite, with parameters such as volume fraction, grain size, and temperature has been studied.
Abstract: The variation of electrical resistivity of an insulator‐conductor composite, namely, wax‐graphite composite, with parameters such as volume fraction, grain size, and temperature has been studied. A model is proposed to explain the observed variations, which assumes that the texture of the composite consists of insulator granules coated with conducting particles. The resistivity of these materials is controlled mainly by the contact resistance between the conducting particles and the number of contacts each particle has with its neighbors. The variation of resistivity with temperature has also been explained with the help of this model and it is attributed to the change in contact area.
103 citations
TL;DR: In this paper, the authors measured the sodium ion resistivity of polycrystalline β-alumina as a function of temperature for fine-grained and coarsegrained specimens with a chemical composition of 8.80 Na20-0.75 Li2O-90.45 A12O3 (wt%).
Abstract: The sodium ion resistivity of lithia-stabilized polycrystalline β”-alumina was measured as a function of temperature for fine-grained and coarse-grained specimens with a chemical composition of 8.80 Na20-0.75 Li2O-90.45 A12O3 (wt%). A model is presented which explains the dependence of sodium ion resistivity on grain size. Using the model the activation energy was determined for the transport of sodium ions across a grain boundary in this form of sodium β”-alumina.
94 citations
91 citations
TL;DR: Grain size frequency distributions of the ≥ 1 mm size fractions have been measured for 19 C2 and C3 carbonaceous chondrites (7 CM2, 5 CO3, 6 CV3 and 1 CV2).
Abstract: Grain size frequency distributions of the ≥ 01 mm size fractions have been measured for 19 C2 and C3 carbonaceous chondrites (7 CM2, 5 CO3, 6 CV3 and 1 CV2) The grain size frequency distribution curves and summary statistics are remarkably similar for the CM2 and CO3 meteorites, with ranges of median grain size from 236φ to 267φ and graphic mean grain size from 220φ to 259φ The CV3 specimens are distinctly coarser than the CM2 and CO3 meteorites and have a wider range of grain size summary statistics The grain size frequency data for fluid drop chondrules and for lithic chondrules show approximately the same size frequency characteristics as the more abundant particles in each of the petrologic subgroups If the chondrules and other particles were produced by different mechanisms or in different environments, an extremely effective size sorting process is required to produce the observed grain size frequency distributions Alternatively, most of the particles and the observed grain size frequency distributions might have been produced by small impacts into an immature, accretionary regolith The strong similarity between the grain sizes of the CM2 and CO3 meteorites, together with previously recognized chemical similarities, suggest a genetic relationship between the two petrologic subgroups The grain size frequency distributions of chondrules and other particles in CM2 and CO3 meteorites are different from those found previously in ordinary chondrites
88 citations
TL;DR: In this article, X-ray microradiographic examination supported by optical and SEM observations was used to study crack propagation in various ceramics, including glasses and cubic and non-cubic polycrystalline bodies of different grain sizes.
Abstract: X-ray microradiographic examination supported by optical and SEM observations was used to study crack propagation in various ceramics, including glasses and cubic and noncubic polycrystalline bodies of different grain sizes. The nature of crack propagation in ceramics was often extremely complex. While cracks in glassy materials were generally simple, as would be expected, in cubic and non-cubic polycrystalline specimens both wandering and branching of cracks was observed. In cubic materials, wandering and branching occurred on the scale of the grain size, while in fine grain, non-cubic materials these were on a multi-grain scale. Results are consistent with the grain size dependence of fracture energy. Elastic anisotropy and thermal expansion anisotropy were suggested as major factors in crack wandering and branching.
TL;DR: In this paper, the statistical approach to the problem of grain growth was used to study the process in material without texture and it was found that the present theories of normal grain growth do not give an adequate description of the process as they fail to take into account the effects of retarding force and the texture of material.
TL;DR: In this article, the authors compared the observed grain size distributions and growth rate with the theoretical predictions of Wagner, Lifshitz and Slyozov, Lay, and Ardell, showing that the grain growth is larger with less matrix fraction in the specimens and this result provides an evidence for the diffusion controlled grain growth during the liquid phase sintering of this alloy.
Abstract: In sintered W-Ni alloys with 1,7, and 30 wt pct Ni the tungsten grain growth in liquid matrix at 1540°C was investigated. The observed grain size distributions and growth rate are compared with the theoretical predictions of Wagner, Lifshitz and Slyozov, Lay, and Ardell. In the 70 pct W-30 pct Ni alloy the tungsten particles settled to the bottom of the specimens immediately upon melting of the matrix, but the spherical grain shape is maintained during the initial stage of annealing. In these specimens the linear intercept distribution of the grains agrees with the prediction of the LSW (Lifshitz, Slyozov, and Wagner) theory for the reaction controlled growth mechanism. On the other hand the growth rate appears to follow the t1/3 law predicted for the diffusion controlled mechanism. These results are consistent with Lay and Ardell's theory in which the concentration gradient around grains is inversely proportional to the average grain size in the limit of small matrix fraction. In the alloys with 1 and 7 pct Ni a meaningful comparison of the observed linear intercept distribution of the grains with theoretical predictions is difficult because of grain contact flattening due to densification. The grain growth is larger with less matrix fraction in the specimens and this result provides an evidence for the diffusion controlled grain growth during the liquid phase sintering of this alloy.
TL;DR: In this paper, the occurrence of deformation twins and the residual volume fraction were observed to depend upon peak pressure, P, pulse duration, Δt, and the average grain size of the initial sheet material, D.
TL;DR: In this paper, a superplastic quasi-single phase copper alloy, containing a cobalt-rich dispersion, was studied and the authors found that the mechanical properties of the alloy are essentially identical to those of super-plastic eutectic and eUTectoid alloys.
TL;DR: Uniaxial compression tests were conducted on polycrystalline-ice samples with random c-axis orientation and steady-state creep rates were determined as mentioned in this paper, and experiments were performed on both inclusion-bearing and inclusion-free ice and were run at constant stress and constant temperature.
Abstract: Uniaxial compression tests were conducted on polycrystalline-ice samples with random c-axis orientation and steady-state creep rates were determined. Experiments were conducted on both inclusion-bearing and inclusion-free ice and were run at constant stress and constant temperature. During freezing, the presence of inclusions in low concentrations inhibits crystal growth; variations in the volume-fraction of inclusions thus result in variations in ice-crystal size. The creep rate of polycrystalline ice at high temperatures and moderate stresses is extremely sensitive to variations in ice-crystal size. Due to an apparent inversion between dislocation-controlled creep and diffusion-controlled creep, the optimum grain size for creep resistance is about 1.0 mm. Increasing or decreasing the average crystal size from this critical value results in an increase in secondary-creep rate.
TL;DR: In this paper, the authors investigated the uniaxial tensile stress-strain behavior of longitudinal and transverse texture Zircaloy-2 and −4 specimens over the range of experimental conditions: temperature 700-1400°C, strain rate 10−6-10−1 s−1, oxygen concentration 0.11-2.0 wt.% and grain size 5-55 μm.
TL;DR: In this paper, the authors measured the yield strength of well-annealed, polycrystalline Zr3 Al with respect to temperature, strain rate and grain size, and showed that at temperatures below ∼-875 K, yielding is controlled by dislocation generation and by the subsequent transmission of slip across grain boundaries.
TL;DR: In this article, the formation range of iron oxides was determined as functions of the substrate temperature and the deposition rate at an oxygen pressure of 4×10-4 Torr.
Abstract: Films of iron oxides such α-Fe3O3 and Fe3O4 were prepared by evaporating iron in a low pressure atmosphere of oxygen gas and investigated by X-ray and electron diffraction and Mossbauer effect measurements. The formation range of iron oxides was determined as functions of the substrate temperature and the deposition rate at an oxygen pressure of 4×10-4 Torr. The oxide film consisted of fine grains, and the grain size of Fe3O4 increased with increase of the film thickness and the substrate temperature. Magnetic properties were investigated. The coercivity was found to increase up to 1000 Oe with the oxidation of the as-deposited Fe3O4 films. The origin of such high coercivity was briefly discussed.
TL;DR: In this article, the transformation of amorphous Si layers to polycrystalline material induced by Q-switched ruby laser single pulses of 20 and 50 nsec duration has been investigated.
Abstract: The transformation of amorphous Si layers to polycrystalline material induced by Q‐switched ruby laser single pulses of 20 and 50 nsec duration has been investigated. The analysis has been performed by transmission electron microscopy and by channeling measurements using 2.0‐MeV He+ Rutherford backscattering. The average grain size of the polycrystalline layers increases with the incident energy density of the laser pulse in the range 0.6–1.7 J/cm2. A transition to single‐crystal layers is found for incident energy densities around 2.0 J/cm2. The grain size correlates with incident energy density (J/cm2) rather than incident power density (MW/cm2) for these pulse durations.
TL;DR: The beaches of Alexandria extend for 38 km and are covered with well-sorted sands that locally differ in texture and origin The heavy minerals encountered in these sands have the same characteristics as those of the Nile deposits as mentioned in this paper.
TL;DR: In this paper, the grain-size effects on the plastic deformation behavior of titanium at 295 K and 575 K were determined by stress-strain measurements and transmission electron microscopic (TEM) observations of deformation substructures.
TL;DR: In this article, the dependency of average grain diameter on deposition conditions is discussed, and the I-V curves, spectral responses, and minority carrier diffusion lengths are presented for photovoltaic devices having grain sizes in the range 0.2 to 5 μm.
Abstract: Vacuum deposited, polycrystalline silicon films were fabricated into planar photovoltaic diodes by double diffusion techniques. Scanning electron microscopy showed that the crystallites are columnar in shape, with grain lengths several times larger than grain diameters. The dependency of average grain diameter on deposition conditions is discussed. Secondary ion mass spectrometry was used to obtain doping profiles and junction depths. Dark and illuminated I-V curves, spectral responses, and minority carrier diffusion lengths are presented for photovoltaic devices having grain sizes in the range 0.2 to 5 μm. Samples formed on sapphire and on a special alkaline-earth aluminosillcate glass processed under the same conditions had similar photovoltaic characteristics. Data on open-circuit voltage, short-circuit current, and solar cell efficiency are presented as functions of average grain diameter.
Patent•
29 Dec 1978
TL;DR: In this article, a method of manufacturing a thin ribbon of magnetic material having a high permeability and excellent flexibility and workability comprising the combination of steps of melting a magnetic material consisting of essentially of by weight 4-7% of aluminum, 8-11% of silicon and the remainder substantially iron and inevitable impurities at a temperature of between a melting point and a temperature not exceeding 300° C.
Abstract: A method of manufacturing a thin ribbon of magnetic material having a high permeability and excellent flexibility and workability comprising the combination of steps of melting a magnetic material consisting of essentially of by weight 4-7% of aluminum, 8-11% of silicon and the remainder substantially iron and inevitable impurities at a temperature of between a melting point and a temperature not exceeding 300° C. from the melting point, and necessary subingredient of less than 7%, ejecting thus obtained melt under a pressure of 0.01-1.5 atm. through a nozzle onto a moving or rotating cooling substrate, cooling super-rapidly the melt on the rotating surface of said cooling substrate at a cooling rate of 10 3 -10 6 ° C./sec so as to have a high initial permeability of more than 10 4 , a low coercive force of less than 0.10 Oe and an excellent flexibility, forming a thin ribbon having a compact and fine grain size structure substantially without existing of the ordered lattice, and annealing thus obtained thin ribbon at a temperature of between 600° to 1,000° C. for 1 minute to 5 hours, more preferably 1 to 100 minutes so as to obtain a columnar crystal structure by promoting the growth of crystal grain size.
TL;DR: In this article, the spatial variation of minority-carrier diffusion length in the vicinity of a grain boundary for a polycrystalline silicon sheet has been measured by the use of the EBIC technique.
Abstract: The spatial variation of minority-carrier diffusion length in the vicinity of a grain boundary for a polycrystalline silicon sheet has been measured by the use of the EBIC technique. The effect of such a variation on solar-cell output has then been computed as a function of grain size. Calculations show that the cell output drops considerably for grain size smaller than three times the bulk diffusion length.
TL;DR: The electrical resistivity ρ of Mo films evaporated by an electron-beam gun onto SiO2/Si substrates has been studied in relation to the film structure and purity as mentioned in this paper.
Abstract: The electrical resistivity ρ of Mo films evaporated by an electron‐beam gun onto SiO2/Si substrates has been studied in relation to the film structure and purity The resistivity was profoundly influenced by the substrate temperature during deposition Ts but was almost independent of film thickness d if d exceeded 1000 A When the films were heat treated at above 700°C, ρ decreased as the grain size increased These results can be explained if one assumes that the resistivity is due to grain‐boundary scattering The reflection coeficient of the electrons at grain boundaries R depends on Ts, but shows no change with heat treatments at temperatures up to about 1000°C(R =041/021 for Ts=300/600°C) It is shown that R is proportional to oxygen content in the grain boundaries
TL;DR: In this paper, the authors applied the austenite ⇆ martensite cylcic heat treatment on Fe-15Ni-5−30Co−5−10Mo-0−2Ti alloys with initial coarse austenitic grain size.
TL;DR: In this paper, a detailed densification model is presented which describes the dependence of densification on time, burn-up, temperature, density, pore size distribution, and grain size.