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Showing papers on "Grain size published in 1977"


Book ChapterDOI
TL;DR: In this paper, an approximate theoretical relation is derived which relates stress during steady state creep to both subgrain size and dynamically recrystallized grain size, based on equating the dislocation strain energy in the grain boundary to that in the enclosed volume.
Abstract: An approximate theoretical relation is derived which relates stress during steady state creep to both subgrain size and dynamically recrystallized grain size. The relation results from equating the dislocation strain energy in the grain boundary to that in the enclosed volume. Available data on metals and silicates are in excellent agreement with the theory. For paleopiezometry, the recrystallized grain size must be preserved by quenching, by cooling under stress, or by inhibition of grain growth by intimate mixture of two or more phases. In general, stress may be underestimated using rocks in which grain size has been reduced by dynamic recrystallization, especially if the grain size is very small. Stress may be overestimated using coarse grained rocks in which the grain size has increased toward the steady state value. Quantitative limits remain to be established. The theoretical relation can in principle be applied to any metal or mineral if only the effective isotropic elastic moduli and the Burgers vector are known. When used as a paleopiezometer, the technique indicates that high stresses on the order of 100 MPa are not infrequently associated with mantle diapirism and with large scale thrust faulting. Consideration of the Mt. Albert ultramafic body suggests that texturally inferred stresses from peridotite massifs and from ultramafic xenoliths in alkali olivine basalts might reflect either horizontal variations in stress across a rising diapir or else a vertical variation in stress as defined by the pyroxene geobarometer (Mercier et al. 1977). In either case the stresses are probably characteristic of local diapirism. Stresses characteristic of global upper mantle flow might be inferred from xenoliths originating from above kimberlite-producing diapirs.

515 citations


Journal ArticleDOI
TL;DR: In this article, tensile-stress-strain data over a strain range from 0.2 to 30% were obtained at room temperature for 99.999 and 99.5% aluminium as a function of grain size.

422 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of grain size distribution on shear moduli of normally consolidated disturbed sands for shear strain ranging from 10-6 to 10-4 were investigated and it was concluded that it is preferable to conduct resonant-column tests on the sands of interest.

306 citations


Journal ArticleDOI
TL;DR: The dependence of minority carrier lifetime (τ) on the doping concentration N d, grain size d and interface state density N is at the grain boundaries in polycrystalline semiconductors has been calculated analytically as discussed by the authors.
Abstract: The dependence of minority carrier lifetime (τ) on the doping concentration N d , grain size d and interface state density N is at the grain boundaries in (n-type) polycrystalline semiconductors has been calculated analytically. The recombination velocity at grain boundaries is enhanced by the diffusion potential V d adjacent to the boundaries, and ranges from \simeq 10^{2} to 106cm . s-1depending on N is and N d . Under illumination, the population of the interface states is altered considerably from its dark level and as a result, V d decreases to that value which maximizes recombination (equal concentrations of electrons and holes at the boundary). This causes τ to decrease with increasing N d . Sample calculations for polycrystalline silicon show that for low angle boundaries with interface state densities of \simeq 10^{11} cm-2eV-1, τ decreases from 10-6to 10-10s as the grain size is reduced from 1000 to 0.1 µm (for N_{d} = 10^{16} cm-3). For a constant grain size, τ decreases with increasing N d . The open-circuit voltage of p-n junction solar cells decreases for \tau \leq 10^{-7} s, whereas that for Schottky barrier cells remains at its maximum value until \tau \lsim 10^{-8} s.

259 citations


Journal ArticleDOI
TL;DR: Using a standard RF coil and a transient recorder, it was found that small cracks in quartz and tourmaline single crystals produce exponentially-decaying RF transients with a time constant of about 10/sup -5/ s as mentioned in this paper.
Abstract: Fracture of quartz-bearing rocks and other hard piezoelectric materials is associated with radio frequency (RF) electromagnetic emission that can be readily detected in the laboratory. Using a standard RF coil and a transient recorder it was found that small cracks in quartz and tourmaline single crystals produce exponentially-decaying RF transients with a time constant of about 10/sup -5/ s. Failure of quartz-bearing rocks generates longer and more complex transients, presumably due to interference of radiation emitted by numerous piezoelectric crystals as a result of the sudden drop in piezoelectric field accompanying the release of stress. The spectral content of these transients depends on grain size, shifting to higher frequencies as grain size decreases. This fracture-related emission has a variety of potential geophysical applications ranging from monitoring cracks in rock deformation experiments to studies of electromagnetic effects associated with earthquakes, hydraulic fracture and mine failure.

256 citations



Journal ArticleDOI
TL;DR: In this article, the effects of porosity and grain size on the magnetic properties of NiZn ferrites were examined on groups of specimens with controlled porosity, and both the permeability and the B-H loop were measured.
Abstract: The effects of porosity and grain size on the magnetic properties of NiZn ferrites were examined on groups of specimens with controlled porosity and grain size; both the permeability and theB-H loop were measured. The demagnetizing factor, which is proportional to porosity, was estimated on the basis of the permeability-porosity relation determined. The discussion of the permeability-grain size relation takes into consideration the dependence of domain wall spacing on grain size. The experimental results for the B-H loops indicate that the remanent magnetic flux density is independent of grain size and the coercive field is independent of porosity. Both the remanent magnetic flux density-porosity and the coercive field-grain size relations are explained via the formulas proposed.

219 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of Dy doping and sintering parameters on the properties of BaTiO3 ceramics were studied, and the average grain size decreases with increasing Dy content and is controlled at ∼1.5 μ m by 0.8 at.% Dy.
Abstract: The effects of Dy doping and sintering parameters on the properties of BaTiO3 ceramics were studied. The average grain size decreases with increasing Dy content and is controlled at ∼1.5 μ m by 0.8 at.% Dy. The Curie temperature change, associated with ≤1.2 at.% Dy, is <3°C. The dielectric constant is ∼2600 for specimens doped with 0.8 at.% Dy, calcined at 1200°C, and sintered at 1450°C. The dielectric constant variation with ambient temperature is much less than that of conventional BaTiO3 ceramics. Lattice constant c decreases with increasing Dy concentration whereas a increases slightly. The effects of grain size on dielectric constant, lattice parameters, and linear thermal expansion coefficient are more pronounced than the chemical effects of Dy doping in the ferroelectric state, whereas in the paraelectric state, these characteristics are almost independent of grain size as well as Dy concentration. The decrease in the frequency of occurrence of 90° twins with decreasing grain size implies that internal stress, which develops when BaTiO3 ceramics are cooled below Tc, strongly influences the effects of grain size.

132 citations


Journal ArticleDOI
TL;DR: Work hardening was found nearly independent of grain size for sizes below 1 μm, consistent with an absence of cell formation in sub-micron grain sizes as discussed by the authors. But the slip lengths for small grain sizes were found to be almost independent of strain.

114 citations


Journal ArticleDOI
B. Abeles1
TL;DR: In this article, it was shown that in granular superconductors, in which the grain size is 20-100 A, the charging energy can be orders of magnitude larger than the Josephson coupling energy and superconducting coupling between the grains is quenched unless the grains are in intimate electrical contact.
Abstract: Previous model calculations of the superconducting properties of aggregates of superconducting grains coupled by Josephson tunnel barriers did not take into account the charging energy associated with small metal grains. It is pointed out that in granular superconductors, in which the grain size is 20--100 A, the charging energy can be orders of magnitude larger than the Josephson coupling energy and superconducting coupling between the grains is quenched unless the grains are in intimate electrical contact.

113 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of grain size on tensile yield strength in annealed conditions was investigated for an austenitic stainless steel Type AISI 316L in the temperature range 20-600°C.
Abstract: Effects of nitrogen additions (0.05–0.18%) as well as of grain size on the tensile yield strength (0.2% proof stress) in annealed conditions were investigated for an austenitic stainless steel Type AISI 316L in the temperature range 20–600°C. It was found that the total strengthening contribution from N is composed of two parts, one grain-size independent and the other strongly grain-size dependent. The former is markedly thermal in this temperature interval and should be attributed to a true solid-solution hardening. The latter appears as a pronounced a thermal increase in the grain-size coefficient in the Petch-Hall relation with increasing N content. Thus, in the temperature range 20–600°C, the total strengthening effect from a given addition of N is grain-size dependent, and in fact increases strongly with decreasing grain size. An important consequence of this remarkable behaviour of N is that a comparatively high yield strength, even at elevated temperatures, is achievable through a combinat...

Journal ArticleDOI
TL;DR: In this article, the authors carried out a systematic experimental study of fracture in materials which contain hard second phase particles and found that the growth of cavities in the grain boundaries was the rate limiting step in the fracture process.
Abstract: We have carried out a systematic experimental study of fracture in materials which contain hard second phase particles. The principal variables in this study were the average size and spacing of the second phase particles, grain size, temperature, and the strain rate. Polycrystalline copper containing a dispersion of silica particles was the material used in these experiments. Three modes of fracture were observed: transgranular necking fracture, fracture by the propagation of intergranular cracks initiated at the surface, and intergranular fracture by grain boundary cavitation throughout the entire specimen cross-section. The transition between the fracture modes was shown to shift systematically with temperature, strain rate, and the microstructure. The intergranular fracture mode was studied in detail. The growth of cavities in the grain boundaries was determined to be the rate limiting step in the fracture process. It was determined that in the range of 10-4 to 10-7 s-1 in strain rate, the dominant growth mechanism of the cavities was power-law creep rather than diffusional transport. The ductility of the material in the intergranular mode of fracture was found to be strongly dependent on the area fraction of the second phase in the grain boundary and on the strain rate sensitivity of the material; it was weakly dependent on the grain size. A theoretical lower bound and a practical upper bound of the ductility in the intergranular fracture mode were established. The results are in qualitative agreement with the data on nickel-base alloys and other materials published in the literature.

Journal ArticleDOI
TL;DR: In this paper, the authors compare plots of grain axial ratio against orientation with those predicted by a mechanism involving homogeneous strain superimposed on initially randomly-oriented elliptical markers, and show that the predicted plots show consistently a broader scatter of O values than the homogeneous model predicts suggesting that other mechanisms have been operative during the deformation.

Journal ArticleDOI
TL;DR: In this paper, an approximate treatment of cavity growth by plastic flow at the tip of a grain boundary crack is given, where the authors derive a creep rupture equation in the form of the Monkman-Grant relation as follows: ϵ t r = (n 2 − 4) 3 In λ 2a 0 2 n+ 2 2πn 2 9 3 ξ n n+2 λ L n − 2 n + 2 σ E n n +2 where ϵge and tr are the creep rate and rupture time, respectively, λ and a

Journal ArticleDOI
TL;DR: In this article, the relative importance of intercrystalline diffusion and intracrystalline creep in crustal deformation in terms of temperature and grain size was evaluated, and it was shown that grain growth may play an important role in delimiting the higher-temperature boundary of the diffusion field.

Journal ArticleDOI
TL;DR: In this paper, the evolution of ferroelectric behavior has been studied as a function of grain size, and the behavior of fine-grained material can be understood in terms of large dipolar clusters which can be frozen into Ferroelectric-like order at low temperatures in the presence of an electric field.
Abstract: By controlled crystallization of the ferroelectric crystalline phase of Pb5Ge3O11 from the glass of the same composition, the evolution of ferroelectric behavior has been studied as a function of grain size. The large‐grained material (≳1 μm) exhibits normal ferroelectric behavior. However, during the initial growth of grains of about 10‐nm dimensions the polarization is unstable and no dielectric anomaly is observed. The behavior of this fine‐grained material can be understood in terms of large dipolar clusters which can be frozen into ferroelectriclike order at low temperatures in the presence of an electric field, but which are too small to stabilize spontaneous ferroelectric order.

Journal ArticleDOI
TL;DR: The growth, structural, and electrical characterization of vacuum-deposited n and p-type CuInTe2 thin films utilizing a high-evaporation-rate technique (≳100 A/s) is reported in this article.
Abstract: The growth, structural, and electrical characterization of vacuum‐deposited n‐ and p‐type CuInTe2 thin films utilizing a high‐evaporation‐rate technique (≳100 A/s) are reported. Complementary transmission electron microscopy (TEM) and Auger electron spectroscopy (AES) are used to investigate the films’ crystalline (grain size, orientation, structure) and compositional (elemental) properties. The effects of substrate temperature on these quantities are presented. A substrate temperature range (400

Journal ArticleDOI
TL;DR: In this article, the authors analyzed the fracture toughness of spheroidized carbon steels at low temperatures in terms of current theories of crack-tip behavior and concluded that in general, fracture toughness decreases with increasing volume fraction and increasing size of the carbide particles.
Abstract: The results of experimental studies of the influence of cementite particles on the fracture toughness of a number of spheroidized carbon steels at low temperatures were analyzed in terms of current theories of crack-tip behavior. The fracture toughness parameterKIC was evaluated by using circumferentially notched and fatigue-cracked cylindrical specimens. The conclusions are summarized as follows: 1) In general,KIC decreases with increasing volume fraction and increasing size of the carbide particles. 2) Crack initiation occurs at the carbide particles. 3) Crack propagation occurs by cleavage if the stress conditions satisfy the Ritchie, Knott and Rice criterion that a critical cleavage stress is achieved over a minimum microstructural size scale. The critical stress is that required to propagate a crack from a particle and the minimum size scale is of the order of 1 to 2 grain sizes. 4) Crack propagation occurs initially by fibrous rupture if the stress intensification is insufficient to attain the critical cleavage stress.


Journal ArticleDOI
TL;DR: In this article, the microstructure of the Nb3Sn grains in commercially produced superconducting filamentary composites has been studied using transmission electron microscopy, showing that the mean grain size increased with annealing time and temperature while the degree of columnar growth decreased at higher temperatures.
Abstract: The microstructure of the Nb3Sn grains in commercially produced superconducting filamentary composites has been studied using transmission electron microscopy. The mean grain size increased with annealing time and temperature while the degree of columnar growth decreased at higher temperatures. Correlation of grain size and superconducting properties showed that the maximum pinning force was obtained for a grain size of about 800 A.

Journal ArticleDOI
TL;DR: In this paper, the grain boundary concentration profiles of alloy additions in an A1-5.5 pct Zn-2 were measured using an Auger electron spectroscopy (AES).
Abstract: Auger electron spectroscopy (AES) has been used to measure the grain boundary concentration profiles of alloy additions in an A1-5.5 pct Zn-2.5 pct Mg ternary in as-quenched, under-, peak-, and over-aged conditions. The AES depth profiles show marked segregation of Mg and Zn to the grain boundary, in contrast to that reported previously on similar A1 alloys. It is found that this apparent contradiction can be resolved by exploiting the plasmonloss features of the AES spectra to help elucidate the grain boundary segregation. With the AES/plasmon-loss measurements, one can determine not only the concentration of Mg and Zn at the grain boundary, but also the metallurgical environments surrounding the alloy additions. It is shown that, for over-aged specimens of the Al alloy, only a fraction of the total Mg at the grain boundary is incorporated in MgZn2 precipitates, the remainder being segregated to within a few atomic layers of the boundary.

Journal ArticleDOI
TL;DR: In this article, the authors derived the fracture toughness of the bulk alloy is composed of a trans-crystalline portion pt = (1 − pi) and an inter-crystaline portion pi and can be derived from the partial fracture toughness KICi, and kICiKIC = KIciPt + (1−Pi)KICi.

Journal ArticleDOI
TL;DR: In this article, the critical stress-intensity factor, K1C, and fracture strength, σf, have been investigated on both hot-pressed and sintered lithia-stabilized β-alumina.
Abstract: The critical stress-intensity factor, K1C, and the fracture strength, σf, have been investigated on both hot-pressed and sintered lithia-stabilized β”-alumina. The hot-pressed material possessed a strong preferred orientation with many of the basal planes aligned perpendicular to the direction of hot-pressing. Both K1C and σf were found to be orientation-dependent. Two regimes of fracture were identified. In fine-grained material (<120 μm), the strength was slightly dependent on grain size. For larger grain sizes, the strength decreased rapidly with increasing grain size and the fracture mode was almost entirely transgranular. The K1C values for sintered β”-alumina were in the same range as those obtained on the hot-pressed material.

Journal ArticleDOI
TL;DR: In this paper, a fine grained microduplex structure was obtained in Zr-2.5% Nb alloys by continuous recrystallisation in the α-β-region.

Journal ArticleDOI
TL;DR: In this paper, the authors examined the creep properties of polycrystalline A12O3 (grain size 14 to 65 μm) under compressive stresses of between 4,000 and 18,000 psi (27.6 and 124 MPa) in the range 1600° to 1700°C.
Abstract: The creep properties of polycrystalline A12O3 (grain size 14 to 65 μm) were examined under compressive stresses of between 4,000 and 18,000 psi (27.6 and 124 MPa) in the range 1600° to 1700°C. Two distinct types of behavior were observed. The creep rate of medium-grained specimens (14 to 30 μm) could be described by ασ1.2/d2 where σ is the applied stress and d is the grain size. These results are consistent with the Nabarro-Herring creep mechanism. For the coarse-grained (65 μm) specimens, the creep rate was related to the stress by ασ2.6. This behavior was not related to cracking; instead, a dislocation mechanism was thought to be rate-controlling. Considerable evidence for grain-boundary sliding was seen, and measurements showed that grain-boundary sliding contributed between 46 and 77% of the total strain in the 3 medium-grained specimens examined and between 38 and 50% in the 3 coarsegrained specimens examined.

Journal ArticleDOI
TL;DR: In this article, the authors achieved critical current densities of over 1.8×106 A/cm2 at 4.2°K and 150 kG in Nb3Al tapes rapidly quenched from the liquid state at rates of 105-106°C/sec.
Abstract: Critical current densities of over 1.8×106 A/cm2 at 4.2 °K and 150 kG have been achieved in Nb3Al tapes rapidly quenched from the liquid state at rates of 105–106 °C/sec. The superconducting transition temperature is about 16 °K, indicating a relatively high degree of order, and increases to 18.4 °K upon annealing at 750 °C. The observed microstructure depends sensitively on the quenching rate and consists of small submicron grains surrounded by a thin boundary layer of different composition. The grain size is roughly inversely proportional to the temperature gradient during quenching. The quoted critical current densities, the highest observed to date in any superconductor, should be regarded as a lower limit of the material critical value imposed by the heating problems due to the contact resistance.

Journal ArticleDOI
TL;DR: In this article, the creep of pure polycrystalline magnesium has been investigated at stresses of 6 MPa and temperatures from 150 to 325°C using both spring and tensile specimens.
Abstract: The creep of pure polycrystalline magnesium has been investigated at stresses beluw 6 MPa and temperatures from 150 to 325°C using both spring and tensile specimens. Examination of the grain size and temperature dependence of the creep rate revealed that, at the lower stresses, deformation occurred by the grain boundary diffusion creep mechanism of Coble, although the rate depended upon stress in a Bingham rather than a Newtonian manner, i.e. there was a threshold stress below which no diffusion creep occurred. At the lowest temperatures, threshold stresses ∼ 1 MPa were found in fine-grained material, decreasing to ∼0.1 MPa as the grain size and temperature were increased. Existing theories were unable to account for the magnitude of the threshold stress. Calculation of magnesium grain boundary self-diffusivity from the creep data gives a value of wDgb = 8 × 10−10 exp -(l05 × 103/RT) m3 S−1 where R is in J mol−1 K−l and w is the grain boundary width.

Journal ArticleDOI
TL;DR: In this paper, the effect of grain size on the thermal diffusivity of polycrystalline MgTi2O5 from 25° to 800°C was studied.
Abstract: The laser flash technique was used to study the effect of grain size on the thermal diffusivity of polycrystalline MgTi2O5 from 25° to 800°C. Microcracking decreased the thermal diffusivity by as much as a factor of two with the decrease increasing with increasing grain size. When specimens were heated then cooled, the thermal diffusivity exhibited a horizontal flat figure-eight hysteresis. This hysteresis, which appeared to be a function of the thermal history, was attributed to a balance between crack healing, or closure, at high temperatures and the growth of existing cracks or the formation of new cracks during cooling.

Journal ArticleDOI
TL;DR: In this article, columnar grains and twins were observed in transmission electron micrographs of both Cu and Ni sputter deposits, but equiaxed structures either alone or mixed with columnar grain were also observed.

Journal ArticleDOI
C. Lanza1, Harold J. Hovel1
TL;DR: In this article, the effect of grain size on the short-circuit current and AM1 efficiency of polycrystalline thin film InP, GaAs, and Si Schottky barrier solar cells was investigated.
Abstract: Numerical calculations have been made of the effect of grain size on the short-circuit current and the AM1 efficiency of polycrystalline thin film InP, GaAs, and Si Schottky barrier solar cells. Si cells 10 µm thick are at best 8 percent efficient for 100-µm grain sizes; 25-µm-thick Si cells can be about 10 percent efficient for this grain size. GaAs cells 2 µm thick can be 12 percent efficient for grain sizes of 3 µm or greater.