Showing papers on "Grain boundary published in 1978"
TL;DR: In this paper, a criterion for the initiation of dynamic recrystallization during hot working is proposed based on the contention that the reduced driving force due to concurrent deformation modifies the normal energy balance which defines the conditions for nucleation of new grains.
369 citations
TL;DR: In this paper, it was shown that gram boundary motion can be induced by changing the composition by means of grain boundary diffusion, and the experimental results can be used to evaluate rather directly the grain boundary diffusivity and mobility.
323 citations
TL;DR: In this article, the electrical transport properties of polycrystalline silicon have been characterized as a function of temperature on both bulk specimens and individual grain boundaries in this material and potential probe measurements show that a large spread in grain-boundary impedances exist in these higher-doped specimens.
Abstract: We have characterized the electrical transport properties of neutron‐transmutation‐doped polycrystalline silicon. Zero‐bias measurements of resistance have been made as a function of temperature on both bulk specimens and individual grain boundaries in this material. Below a doping level of ∼2×1015 phosphorus/cm3, the bulk resistance has a nearly Arrhenius behavior with an activation energy of ∼0.55 eV; above this donor concentration the resistivity is markedly curved on an Arrhenius plot with values of slope which decrease with decreasing temperature. Potential probe measurements show that a large spread in grain‐boundary impedances exist in these higher‐doped specimens. We compare our data to theoretical expressions for current flow across grain‐boundary potential barriers and good agreement is observed; these comparisons indicate that the largest grain‐boundary state densities observed in our samples consist of ∼6×1011 available single‐electron‐states/cm2 located within ∼0.2 eV from the center of the f...
252 citations
Proceedings Article•
01 Jan 1978
TL;DR: In this article, the electrical transport properties of polycrystalline silicon have been characterized as a function of temperature on both bulk specimens and individual grain boundaries in this material and potential probe measurements show that a large spread in grain-boundary impedances exist in these higher-doped specimens.
Abstract: We have characterized the electrical transport properties of neutron‐transmutation‐doped polycrystalline silicon. Zero‐bias measurements of resistance have been made as a function of temperature on both bulk specimens and individual grain boundaries in this material. Below a doping level of ∼2×1015 phosphorus/cm3, the bulk resistance has a nearly Arrhenius behavior with an activation energy of ∼0.55 eV; above this donor concentration the resistivity is markedly curved on an Arrhenius plot with values of slope which decrease with decreasing temperature. Potential probe measurements show that a large spread in grain‐boundary impedances exist in these higher‐doped specimens. We compare our data to theoretical expressions for current flow across grain‐boundary potential barriers and good agreement is observed; these comparisons indicate that the largest grain‐boundary state densities observed in our samples consist of ∼6×1011 available single‐electron‐states/cm2 located within ∼0.2 eV from the center of the f...
237 citations
TL;DR: In this paper, a kinetic approach is used to explain the nucleation of cavities in grain boundaries at elevated temperature, under the influence of a tensile stress, vacancies cluster together and form cavities.
237 citations
TL;DR: In this article, the authors investigated the grain growth phenomena of heavily phosphorus-implanted polycrystalline silicon films owing to high temperature annealing by transmission electron microscope and found that phosphorus doping in excess of is found to enhance grain growth.
Abstract: Grain growth phenomena of heavily phosphorus‐implanted polycrystalline silicon films owing to high temperature annealing are investigated by transmission electron microscope. Phosphorus doping in excess of is found to enhance grain growth. This growth is broken down into primary and secondary recrystallization. Isochronal annealing reveals the activation energies for these as 2.4 and 1.0 eV, respectively. The driving force of the primary recrystallization is found to be the interface energy. Therefore, the elementary process behind the primary recrystallization is attributed to silicon diffusion across the grain boundary region.
234 citations
TL;DR: In this article, a model for the formation of annealing twins in f.c. metals and alloys is proposed, which does not require associated migration of the existing grain boundaries.
206 citations
TL;DR: In this article, the role of deformation incompatibility in crack nucleation is discussed and the nature of Stage I growth (intergranular) in high strain fatigue is described and defined in terms of bulk slip in the grains adjacent to the crack.
204 citations
TL;DR: In this paper, an analysis of the normal tractions acting on grain boundaries in a solid with a perfectly regular hexagonal grain structure deforming via diffusional creep is made, where restrictions are placed on the allowable diffusion paths solely by requiring that the normal stresses on opposite sides of a grain boundary be identical.
197 citations
TL;DR: The diffusive growth rate of a grain boundary cavity is calculated under conditions where vacancies are created non-uniformly across the boundary as discussed by the authors, where power-law creep relaxes the strain due to diffusive atom plating which occurs preferentially near the cavity and allows increased growth rates.
Abstract: The diffusive growth rate of a grain boundary cavity is calculated under conditions where vacancies are created non-uniformly across the boundary. Away from the boundary, power-law creep relaxes the strain due to the diffusive atom plating which occurs preferentially near the cavity and allows increased growth rates. At high stresses the growth rate is proportional to the creep strain rate or stress to a high power and at low stresses the growth rate is proportional to stress.
193 citations
TL;DR: In this article, the effects of alloy purity and state of aging on the fracture mechanism and resultant toughness of pure Al-Cu alloys, and commercial duralumin were examined, and good agreement was obtained between experimental results of toughness and those predicted from a knowledge of the tensile properties.
Abstract: The object of the paper is to examine the effects of alloy purity and state of aging on the fracture mechanism and resultant toughness of pure Al-Cu alloys, and commercial duralumin. In pure alloys, the transition from a shear to an intergranular mode of fracture with overaging is associated with changes in the nature and size of the matrix precipitate, which affect the slip character. In the corresponding commercial purity alloys, no such fracture mode transition occurs. The presence of second-phase dispersoids inhibits planar slip, and in the overaged state inclusion-matrix interfaces present a suitable alternative site to the grain boundaries for strain accumulation, resulting in debonding leading to the initiation of voids, which subsequently grow and coalesce. The fracture toughness, as conventionally measured, indicates the material’s resistance to crack initiation rather than propagation and is effectively independent of fracture mode. The work hardening capacity has a marked effect on void size, and is shown to be a sensitive indicator of fracture toughness in both pure and commercial alloys. Based on a simple model, good agreement is obtained between experimental results of toughness and those predicted from a knowledge of the tensile properties.
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.
Patent•
18 Dec 1978
TL;DR: Nickel base superalloy single crystal articles formed from an alloy family and heat treated are described as is the process employed as discussed by the authors, and the articles are substantially free from cobalt and the grain boundary strengtheners such as carbon, boron and zirconium.
Abstract: Nickel base superalloy single crystal articles formed from an alloy family and heat treated are described as is the process employed. The articles are substantially free from cobalt and the grain boundary strengtheners such as carbon, boron, and zirconium. The heat treatment process homogenizes the microstructure, and refines the gamma prime morphology.
TL;DR: In this article, the details of crack nucleation phenomena in the high strain fatigue of OFHC copper have been studied by optical microscopy and two-beam interferometry, and the plastic instability mechanism of cracks has been ruled out in polycrystalline metals in favor of one which takes into account the detailed crystallographic aspects of slip in adjoining grains.
TL;DR: In this article, microstructural analysis of a 10 mol% Y/sub 2/O/sub 3/ fluxed hot-pressed silicon nitride reveals that, in addition to the yttrium-silicon oxynitride phase located at the multiple Si/Sub 3/N/sub 4/ grain junctions, there is a thin boundary phase 10 to 80 A wide separating the silicon nitric oxide and the oxynitic grains, suggesting that densification occurred by a liquid-phase ''solution-reprecipitation'' process.
Abstract: Detailed microstructural analysis of a 10 mol% Y/sub 2/O/sub 3/ fluxed hot-pressed silicon nitride reveals that, in addition to the yttrium-silicon oxynitride phase located at the multiple Si/sub 3/N/sub 4/ grain junctions, there is a thin boundary phase 10 to 80 A wide separating the silicon nitride and the oxynitride grains. Also, x-ray microanalysis from regions as small as 200 A across demonstrates that the yttrium-silicon oxynitride, Y/sub 2/Si(Si/sub 2/O/sub 3/N/sub 4/), phase can accommodate appreciable quantities of Ti, W, Fe, Ni, Co, Ca, Mg, Al, and Zn in solid solution. This finding, together with observations of highly prismatic Si/sub 3/N/sub 4/ grains enveloped by Y/sub 2/Si(Si/sub 2/O/sub 3/N/sub 4/), suggests that densification occurred by a liquid-phase ''solution-reprecipitation'' process.
TL;DR: A mathematical analysis based on the Mayadas-Shatzkes model indicates that an effective mean free path may be defined in order to describe electronic conduction in both thin polycrystalline and monocrystalline metallic films as discussed by the authors.
TL;DR: In this paper, the processes that occur at grain boundaries during high temperature creep at low strain rates have been studied by scanning electron microscopy of a fiducial grid and by transmission electron microscope of pure aluminium.
Abstract: The processes that occur at grain boundaries during high temperature creep at low strain rates have been studied by scanning electron microscopy of a fiducial grid and by transmission electron microscopy mainly of pure aluminium. These and other observations are interpreted in terms of a dislocation model for grain boundary behaviour during high temperature creep.
TL;DR: In this paper, it was shown using Auger electron spectroscopy that impurity segregation to grain boundaries in iridium was not necessary for grain boundary fracture to occur, thereby demonstrating that intergranular brittle fracture in polycrystalline iridium is also intrinsic and not impurity related.
Abstract: Brittle fracture in fcc metals is uncommon. It is not common knowledge that single crystals of iridium, a high melting point fcc metal, fail by brittle cleavage at room temperature. Furthermore, polycrystalline iridium fails predominantly by brittle inter granular fracture at temperatures below 1000°C. With the aid of several models of brittle fracture we have demonstrated that cleavage in iridium is intrinsic, resulting from apparently very strong and directed atomic binding forces. Intergranular fracture in iridium has been generally assumed to arise from the segregation of harmful impurities to the grain boundaries. We were able to demonstrate using Auger electron spectroscopy that impurity segregation to grain boundaries in iridium was not necessary for grain boundary fracture to occur, thereby demonstrating that intergranular brittle fracture in polycrystalline iridium is also intrinsic and not impurity related.
TL;DR: In this article, the faceting of grain boundary planes of low energy has been studied and some low energy boundary planes identified Tilt boundaries with a 〈110〉 misorientation axis have been found to facet more readily than those with a Ω100〉 axis, where the results have been considered in terms of O -lattices and coincident site lattices.
TL;DR: In this article, the authors classified the circumstances under which steels exhibit intergranular fracture into four general categories: (1) owing to the presence of certain secondary phases at the grain boundaries; (2) due to thermal treatments which cause impurity segregation to the grain boundary without the precipitation of an observable second phase; (3) owing due to the action of certain environments; and (4) a combination of stress and high temperatures.
Abstract: The circumstances under which steels exhibit intergranular fracture can be classified into four general categories: (1) owing to the presence of certain secondary phases at the grain boundaries; (2) owing to thermal treatments which cause impurity segregation to the grain boundaries without the precipitation of an observable second phase; (3) owing to the action of certain environments; and (4) owing to a combination of stress and high temperatures. In this paper each of these categories and their effects on material properties are reviewed. How the chemical composition of the grain boundary influences and induces intergranular cracking is discussed in detail for all four cases.
TL;DR: In this article, the ac electrical behavior of zirconium oxide with calcium concentrations ranging from 12 to 19 mole% was investigated as a function of frequency, from 100 Hz to 500 kHz, temperature, from 300°C to 900°C, and partial pressure of oxygen, from 10−5 to 1 atm.
TL;DR: In this article, an experimental technique has been developed for implanting water vapor bubbles (H2O(v) of fixed size and spacing along the grain boundaries of polycrystalline silver.
TL;DR: In this article, the grain boundary compositions and the effect of austenitizing temperature on the degree of P segregation in the austenite phase were analyzed by a scanning Auger microprobe.
Book•
01 Aug 1978TL;DR: In this article, a new surface analytic capability is reviewed which can provide a unique picture of a metallic surface by directly imaging, in atomic resolution, the spatial distribution of its constituent species and their depth distribution within the near surface region.
Abstract: Surface properties of metallic solids are of great technological interest. Their influence is felt in areas as diverse as catalysis, corrosion and the plasma stability in magnetic-confinement fusion reactors. In this paper a new surface analytic capability is reviewed which can provide a unique picture of a metallic surface by directly imaging, in atomic resolution, the spatial distribution of its constituent species and their depth distribution within the near surface region. After thoroughly reviewing the experimental technique and emphasizing design parameters and constraints, the analytic capabilities and limitations of the technique are discussed in detail. Examples are given of surface and near surface compositional analysis and the ability to obtain angstrom resolved depth profiles of implanted species having energies less than 100 eV. Although essentially a research technique requiring special sample preparation, the anticipated practical applications of Imaging Atom-Probe Mass Spectroscopy are numerous, ranging from metallurgical studies of grain boundary segragation and pre-precipitate clustering in alloys, to the direct imaging of constituent atoms within large, biological active molecules.
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.
TL;DR: In this article, the segregation of S to grain boundaries in Ni3Al and Ni3(Al, Ti) has been studied using Auger electron spectroscopy and it was shown that S concentration at the grain boundaries decreases more slowly with increasing temperature than would be predicted by segregation models based on a single solute binding energy to the grain boundary.
Abstract: The segregation of S to grain boundaries in Ni3Al and Ni3(Al, Ti) has been studied using Auger electron spectroscopy. The S concentration at the grain boundaries decreases more slowly with increasing temperature than would be predicted by segregation models based on a single solute binding energy to the grain boundaries. This behavior, which can be interpreted as an increase in the effective solute binding energy for a grain boundary as a function of temperature, is consistent with predictions of a model based on the existence of a spectrum of solute binding energies for grain boundaries.
TL;DR: In this paper, anodic polarization curves of amorphous and crystalline Cu 50 Ti 50 and Cu 50 Zr 50 alloys have been examined in various acidic, neutral and alkaline solutions.
Abstract: Corrosion rates and anodic polarization curves of amorphous and crystallinecu 50 Ti 50 and Cu 50 Zr 50 alloys have been examined in various acidic, neutral and alkaline solutions. The amorphous alloys are very stable in acidic and alkaline solutions, but unstable in agressive chloride solutions. The corrosion resistance of these amorphous alloys is higher than that of the crystallized alloys. The high corrosion resistance of amorphous alloys is attributable to the high chemical homogeneity of amorphous alloys without localized crystalline defects such as precipitates, segregates, grain boundaries, etc. Metalloid elements play an important role in the corrosion behavior of amorphous alloys; the addition of phosphorus to amorphous CuTi alloy greatly increases the corrosion resistance, even in 1N HCl.
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