Showing papers on "Grain size published in 1970"

Electromigration Damage in Aluminum Film Conductors

Abstract: Electromigration studies of large‐ and fine‐grain aluminum films showed that fine‐grain films were characterized by a mixed orientation and a grain size of ≈2 μ, and that large‐grain films had a highly preferred 98% 〈111〉 orientation and a grain size of ≈8 μ. Stripes fabricated from the large‐grained films had a consistently longer life, higher activation energy, and lower standard deviation of the life distribution than stripes fabricated from fine‐grained films. These results are interpreted in terms of the nature of flux divergences in the two films. Calculations give the magnitude of vacancy supersaturations at various structural divergences present in the films studied.

The influence of polycrystal grain size on several mechanical properties of materials

Abstract: The ductile-brittle transition, hardness, fatigue, and creep behavior of polycrystalline materials are known to be influenced under certain conditions by the polycrystal grain size. These properties have been correlated, historically, with the material stress-strain behavior. The (Hall-Petch) stress-grain size relations are useful for describing the complete stress-strain behavior for polycrystals and, therefore, these relations provide a reference for understanding the manner in which these other properties should also depend on the grain size. In some cases, the grain size dependence of a particular property follows directly from this connection.

Method for Determining Permeability from Reservoir Rock Properties

Abstract: Porosity and permeability of reservoir sandstones can be related to the primary rock properties of composition, texture, and packing. Permeability is assumed to be largely a function of rectilinear pore size which, in turn, is a function of mean grain size, sorting as expressed by deviation of grain size distribution, mean grain shape, and packing of grains. By means of systematic packings of uniform spherical grains, the size and shape of rectilinear pores can be determined for porosities of 30 to 40 percent. By considering laminar flow of fluids through pores of idealized cross sections, a general equation can be derived in which permeability is a function of the square of the median grain size, of the fifth power of porosity, and of phi percentile deviation. When the equation is applied to clean sands and sandstones of 30 to 40 percent porosity, permeability may be calculated with reasonable accuracy. The agreement between theoretical and measured values suggests that this approach may be applicable to other packings and porosities in subsurface reservoir sandstones.

The Contribution of Grain-Boundary Diffusion to Creep at Low Stresses

Abstract: Experiments are described on the deformation of copper, both in the form of long straight wires and in the form of helices, with the aim of evaluating the importance of diffusion-creep processes, especially in the range where the effect of grain-boundary diffusion is expected to predominate. It is established that at low stresses and elevated temperatures, polycrystalline copper can behave in a Newtonian manner with the primary creep stage of negligible importance. Above a specific temperature, which is shown to vary inversely as the logarithm of the grain size, creep rates agree closely with the Nabarro–Herring equation, and the activation energy is identical with that for lattice self-diffusion. Below this temperature the activation energy is found to be near the value expected for grain-boundary self-diffusion, and the creep rate now varies inversely as the cube of the grain size in agreement with the equation derived by Coble (J. Applied Physics, 1963, 34, 1679). Within the range of the presen...

Polymorphic Behavior of Thin Evaporated Films of Zirconium and Hafnium Oxides

Abstract: Polymorphism in thin evaporated films of zirconium and hafnium oxides was investigated from 100° to 1500°C by electron diffraction and transmission electron microscopy. The films have metastable cubic structures at room temperature and at moderate temperatures. Zirconium oxide, depending on temperature, exists in cubic, tetragonal, and monoclinic forms, whereas hafnium oxide transforms directly from the cubic to the monoclinic structure. The transformation temperatures depend on the oxygen partial pressure. Air annealing of thin films of ZrO2 and HfO2 lowered the temperature of transformation of the tetragonal and the cubic structure into the monoclinic structure by about 150° and 100°C, respectively. The cubic/tetragonal transformation of ZrO2 is monotropic, whereas the tetragonal monoclinic transformation occurs by the typical nucleation and growth mechanism. Determination of grain size in ZrO2 at the tetragonal/monoclinic transformation temperature showed that the transformation occurs when a constant grain size of about 800 A is reached. The oxygen partial pressure, grain size, and temperatures at which the metastable phases exist were correlated. The rate of grain growth is enhanced by increase in oxygen partial pressure. The accelerated transformation in air is attributed to rapid attainment of the critical size; grain boundary energy is an important controlling factor in transformation.

Grain size effects in the strain hardening of polycrystals

Abstract: The degree to which the flow stress of a polycrystal is sensitive to grain size is discussed in terms of the distribution of slip and dislocation structure that develops in the vicinity of grain boundaries as deformation proceeds. The point of view is taken that the two principal classes of grain boundary hardening models, namely, those based on dislocation pile-ups and those based on dislocation density concepts respectively represent special cases of a single rationale developed in this paper. Grain boundary strengthening is intimately related to strain hardening which is affected by slip mode,i.e., the number of slip systems and the ability to cross slip. The effects of substitutional solute elements on grain boundary strengthenings is considered to be a consequence of their influence on slip modes rather than on their interaction with dislocation sources.

Creep in Yttria‐ and Scandia‐Stabilized Zirconia

Abstract: Compression creep measurements at constant load on ZrO2-6 mol% Sc2O3 (grain size ∼1 μm), ZrO2-6 mol% Y2O3 (grain size ∼17 μm), and heat-treated ZrO2-6 mol% Sc2O3 (grain size ∼2 μm) yield activation energies of 89, 86, and 74 kcal/mol, respectively. The creep rates are linearly proportional to the inverse square of the grain size of the material. A stress exponent, n, of 1.5 was found for the scandia-doped zirconia and two regimes, with n=1 and 6, were found for the yttria-doped zirconia. These data, supported by metallographic evidence, are interpreted as showing that n=1 is associated with cation diffusion control of creep, n=6 with local propagation of inter-crystalline cracks, and n=1.5 with a transition region.

Plastic Deformation in Fine-Grain Ceramics

Abstract: Plastic deformation in fine-grain (i.e., ≤ 10 µ)ceramics is discussed. It is shown that fine-grain polycrystals can be exceptionally ductile, the fine grain size enhancing diffusional deformation and grain boundary sliding processes. The deformation is sensitive to both grain size and temperature.

Strength‐Anisotropy‐Grain Size Relations in Ceramic Oxides

Abstract: On the basis of high strengths observed at small grain size and crack formation observed at moderate grain size, a large grain-size dependence of the strength of rutile ceramics was predicted. This dependence was investigated by experiment, and a grain-size exponent greater than -1/3 was found. Tabulating literature data on the grain-size dependence of strength and the degree of anisotropy of several oxide ceramics demonstrated a correlation between the degree of anisotropy and the grain-size exponents; the grain-size exponent increases with increasing anisotropy. The mechanism of fracture of single-phase ceramics composed of anisotropic crystals is discussed.

Effect of Transformation Substructure on the Strength and Toughness of Fe-Mn Alloys

Abstract: Phase transformations in Fe−Mn alloys containing up to 9 pct Mn were studied by optical and electron transmission microscopy. Either equiaxed ferrite, massive ferrite, or massive martensite can form on cooling from austenite. The particular type of transformation product formed was found to depend on the alloy content, austenite grain size, and cooling rate. The mechanical properties of all the transformation products were evaluated using tensile and impact testing and are discussed in terms of the observed microstructural features. Yield strength and impact transition temperature were found to be relatively insensitive to manganese content but were strongly influenced by the transformation substructure and grain size of the transformed phase. In martensite it has been shown that the structural unit analogous to grain size in ferrite is the martensite packet size, which in turn is controlled by the prior austenite grain size. The fracture surface of broken impact specimens and the fracture profile were examined by means of electron and optical microscopy techniques. These fractographic observations were correlated with impact test data and microstructural observations of the various transformation products.

The Effect of Hydrogen on the Deformation and Fracture of Polycrystalline Nickel

Abstract: Polycrystalline nickel (grain size 140 μm) containing 9 ppm hydrogen has been mechanically tested over the range − 196 to + 100° C (77 to 373K) and at strain rates from 0·1 to 0·0001 s−1. The hydrogen causes serrated yielding between − 130 and − 30° C (145 and 245 K), an increase in work-hardening rate between − 160 and + 100° C (115 and 373K), but no increase in yield stress. Hydrogen also weakens the nickel grain boundaries under all testing conditions. The resultant intergranular embrittlement is most marked below − 50° C (225 K) and appears to be enhanced by the occurrence of serrated yielding and grain-boundary shears. It is suggested that a very thin layer of hydride weakens the grain boundaries, but there is no direct evidence to support this.

Determination of Mean Sediment Thickness in the Crust: A Sedimentologic Method

Abstract: Mean sediment thickness, volume of detntal quartz, and grain size distribution of dctrital quartz have been calculated for the total sediment mass of the earth's crust. Sedimentologic and petrographic data were used rather than geochemical data. Results are in good agreement with the earlier estimates based on geochemical arguments. Mean sediment thickness is computed to be 2690 feet and represents the erosion of 7640 feet of crystalline rocks. The percent of detrital quartz in the sediment mass is estimated to be 21.0 percent. The detntal quartz has a mean grain size of 4.0ϕ its frequency-distribution is log-normal with standard deviation of 2.5ϕ. As earlier work has indicated the mean size of quartz from newly disintegrated crystalline rocks to be 0.67 mm, the mean size of 0.06 mm determined for the earth's detrital quartz represents a size decrease of 90 percent by sedimentary processes.

Creep of Polycrystalline MgO and MgO‐Fe2O3 Solid Solutions at High Temperatures

Abstract: Polycrystalline MgO and MgO-Fe2O3 solid solutions (0.10 to 8.08 wt% Fe2O3) were fabricated to almost theoretical density by vacuum hot-pressing. Specimens were creep-tested in air under four-point dead-load conditions between 1000° and 1400°C at stresses between 50 and 550 kg/cm2. Steady-state creep was never achieved in the experiments, which sometimes lasted more than 50 h. The strain rate vs time (t) data were described by an equation of the form =c1/(t+C2)p, which is consistent with the assumptions that creep occurs at least in part by a “viscous” mechanism and that grain growth occurs simultaneously. Doping MgO with Fe2O3 enhanced the viscous contributions to creep and inhibited the nonviscous ones. Creep rates in these specimens increased with increasing Fe2O3 additions. The occurrence of simultaneous grain growth during the high-temperature creep of magnesiowustite (i.e. MgO-Fe2O3 solid solutions) was used in establishing the strain rate vs grain size dependence. The results of this study are consistent with a transition between grain boundary and lattice diffusion mechanisms as the grain size increases (4 to 44 μan). The creep of polycrystalline MgO is a mixed process in that viscous and nonviscous (dislocation) contributions are present.

The nucleation of aluminum grains in alloys of aluminum with titanium and boron

Abstract: The microstructure of a ternary alloy, Al-5 wt pct Ti, 1 wt pct B, has been examined by optical and electron transmission microscopy, by selected area diffraction, and electron probe microscopy, by selected area diffraction, and electron probe microanalysis. Particles of Al3Ti are found at the center of grains and there exist preferred epitaxial orientations between this compound and the surrounding aluminum. Particles containing titanium and boron occur at aluminum grain boundaries and have no preferred configurations with respect to the aluminum or to one another. It is concluded that the active heterogeneous nuclei are therefore Al3Ti and that particles of TiB2, AlB2, or a ternary compound are not active in this alloy. Grain size measurements in binary Al-Ti alloys suggest that particles of a nucleating phase must be present at concentrations as low as 0.01 wt pct Ti, and it is suggested that these could be Al3Ti if the existing binary phase diagram Al-Ti is in error.

Microstructure Development in Yttrium Iron Garnet

Abstract: Sintering and grain-growth rates were determined for yttrium iron garnet as a function of the yttrium/iron ratio. Rates decreased with an increase in this ratio; this behavior is interpreted as a result of the oxygen content variation through the garnet field. For constant sintering time, density and grain size, as well as microstructure-dependent properties, varied through the garnet field. Remanent magnetization and coercive force in particular depended on composition and sintering temperature. The rf field for nonlinear spin-wave excitation, hcrit, measured for dense samples with grain sizes from ∼4 to 30 μm, varied by a factor of four.

The effects of thermal treatment on the austenitic grain size and mechanical properties of 18 Pct Ni maraging steels

Abstract: A technique has been developed for controlling the austenitic grain size of 18 pct Ni maraging steels by thermal treatment alone. This treatment has been applied to two different grades, 250 and 300, of maraging steel, and a large grain size, ASTM 2, was reduced to ASTM 7 in both cases. The process of grain size refinement requires thermal cycling from a temperature belowM f to a temperature considerably above the austenitizing temperature. The minimum austenitic grain size attainable depends on the prior strain in the material as well as the thermal treatment. While significant grain size refinement can be attained by one cycle to the proper temperature, the attainment of the minimum uniform grain size requires several cycles. The effects of austenitic grain size on tensile properties have been investigated both at room temperature and at elevated temperatures. The prior austenitic grain size has a small but measurable effect on the mechanical behavior of aged material at room temperature. The austenitic grain size has a significant effect on the ultimate tensile strength at 1600°F.

Value d0z* for grain boundary electromigration in aluminum films

Abstract: A value of the constant D0Z* for grain boundary electromigration in alluminum thin films is determined to be 3(± 0.5) × 10−2. Generalized curves are provided for (vi/j)T against T−1 for aluminum films. These curves can be used to obtain appropriate ionic velocities at any temperature or current density for films of known grain size.

Apollo 11: Soil Mechanics Results

Abstract: Data were extracted from astronaut observations, television coverage of the moon walk, and returned photographs and samples. It has been determined that the upper few centimeters of the lunar soil in the vicinity of Tranquility Base are characterized by a brownish, medium-gray, slightly cohesive granular soil composed largely of bulky grains in the silt to fine sand size range, with angular to subrounded rock fragments ranging up to 1 m in size distributed throughout the area. The lunar surface at this site is soft to depths of 5 cm to 20 cm, below which the resistance to penetration increases considerably. Although the soil differs considerably in composition and range of particle shapes from a terrestrial soil of the same particle size distribution, it does not appear to differ significantly in its mechanical behavior. The soil, while basically frictional in behavior, exhibits a small amount of cohesion and strong adhesive properties. Preliminary estimates of the in situ soil density gave a value of 1.6 g per cu cm.

Variations in grain‐size and sorting on two kaikoura beaches

Abstract: Summary Two exposed, high‐energy beaches on the Kaikoura coast of New Zealand are composed of sand and gravel derived from a greywacke terrain. Both beaches can be classified as mixed beaches although the sediment varies from dominantly gravel at the ends of the beach to dominantly sand at the centre, through transition zones in which sand and gravel are mixed. Sixty‐four surface samples were analysed for grain size; two sediment parameters, mean grain size (Mz) and sorting (σI), were calculated. A striking feature of the cumulative frequency curves is that both unimodai and bimodal distributions include median sizes over the whole range of sampled material, even though bimodal samples display two strong modes in the sand and gravel grades. The general deficiency lof sediment dn the very coarse sand and granule classes (0 to — 2 F ) noted by numerous authors in many parts of the world is apparent in the poorly‐sorted bimodal samples. However, the best‐sorted samples also occur in these two classes. Mean g...

Process for making nickel-based superalloys

Abstract: A process for making nickel-based superalloys that possess excellent high-temperature properties which includes the steps of providing a metal powder having a controlled amount of oxygen and carbon which is confined and densified at an elevated temperature forming a billet that can be further deformed, if desired, to provide an appropriate shaped component. Thereafter, the billet or deformed part is subjected to heat treatment to effect a growth in the grain size thereof to attain optimum physical properties, whereafter the alloy is carburized to increase the carbon content thereof to a level in excess of about 500 parts per million (ppm) which is performed in a manner so as to preferentially promote carbide formation at the grain boundaries of the alloy, thereby stabilizing the alloy against further grain growth when subjected to elevated temperatures during use.

Method of making a magnetic disc

Abstract: A METHOD OF MAKING MAGNETIC DISC WHEREIN AN ELECTRICALLY CONDUCTING MATERIAL LAYER IS FORMED ON THE SUFACES OF A BASE PLATE MADE BY SHAPING A SYNTHETIC RESINOUS MATERIAL, THEN A MAGNETIC MATERIAL IS APPLIED TO THE COAT BY ELECTRODEPOSITION AND FINALLY THE SURFACES ARE POLISHED BY A POLISHING MATERIAL OF VERY SMALL GRAIN SIZE. THE LAYER OF MAGNETIC MATERIAL FORMED BY ELECTRODEPOSITION HAS ITS SURFACES RENDERED SMOOTH BY THE POLISHING OPERATION BECAUSE MINUTE FISSURES IN THE SURFACES ARE REMOVED AND AT THE SAME TIME THE MAGNETIC MATERIAL LAYER ITSELF IS ANNEALED BY THE HEAT OF FRICTION.

Effect of Surface Finish on Structural Ceramic Failure

Abstract: The relation between fracture strength and surface finish of brittle nonmetallic materials was examined and related to surface-crack theory. Specimens used in an experimental illustration were made of a commercially available 96%-pure alumina with an average grain size of 3.8 μm and a porosity of about 6%. Several groups of specimens, each having a different surface finish, were used in a biaxial ball-and-ring

EFFECTS OF HEAT-TREATMENT ON THE HIGH-TEMPERATURE DUCTILITY AND FRACTURE OF 20 Cr/25 Ni/Nb STABILISED AUSTENITIC STEEL.

Abstract: Stabilisation of 20 Cr/25 Ni steel by niobium not only increased the creep resistance but eliminated the tendency for cracking and thereby enhanced the ductility. No change in density was detected in fine-grained specimens solution-treated at 1000° C until well into tertiary creep, and elongations of 75 to 150% were obtained. After a solution-treatment at 1250° C the creep resistance was further increased and denuded zones were formed near grain boundaries. This caused the strain to be concentrated in grain boundary regions during creep, leading to the formation of both surface- and wedge-cracks at grain boundaries. However, in contrast to a niobium-free steel, these did not nucleate until the end of the secondary creep.

The grain size dependence of the yield, flow and fracture stress of commercial purity silver

Abstract: Heavily cold-rolled sheet material of 99.9 pct purity Ag has been recrystallized at varying temperatures to give average grain diameters,l, in the range between 1 and 60 μ. For this material, the yield stress, flow stress at several strain values, and fracture stress follow the Hall-Petch relation: $$\sigma _\varepsilon = \sigma o_\varepsilon + k_\varepsilon l^{ - 1/2} $$ whereσ e is the flow stress at a particular value of strain, e, ands o e andk e are the experimental constants appropriate to a particular strain value. The range in grain size obtained for this material was sufficiently large to determine that silver can be appreciably strengthened by grain size refinement and that several other relations previously suggested to relate the stress and grain size could be discounted. The finest grain sizes were measured from replicas of etched specimens as viewed with the electron microscope. It is proposed that this type of grain size strengthening may be responsible for the exceptional strength which occurs in certain films of silver fabricated by vapor deposition techniques.

Intergranular brittleness studies in tungsten using auger spectroscopy.

Abstract: The present investigation was aimed at understanding the problem of brittleness in powder metallurgy tungsten by utilizing Auger Electron Emission Spectroscopy as a tool for direct chemical analysis of fracture surfaces Substantial segregation of phosphorus to the grain boundaries was observed in tungsten and the concentration of phosphorus can be related to the ductile-brittle transition temperatures The amount of segregation was dependent upon the grain size—the larger the grain size, the greater the concentration of phosphorus at the grain boundary and the associated embrittlement

Methods and significance of particle and grain-size control in cemented carbide technology*

Abstract: The paper reviews work demonstrating the importance of carbide particle and grain size as regards the preparation and the properties of cemented carbides, and considers the techniques of particle- and grain-size measurement. It is shown that the initial size of the carbide powder influences the grain size in the sintered structure. Means of size-distribution analysis are evaluated. Some problems of accurate quantitative structure analysis and its automation are discussed. The best methods at present available for routine and basic work are outlined and modern devices are described.