Showing papers on "Microstructure published in 1973"
TL;DR: The advantages of a systematic application of the method of virtual power are exemplified by the study of continuous media with microstructure, and the equations of motion for the general micromorphic medium are established for the first time.
Abstract: The advantages of a systematic application of the method of virtual power are exemplified by the study of continuous media with microstructure. Results on micromorphic media of order one are easily found and the equations of motion for the general micromorphic medium are established for the first time. Various interesting special cases, which have been previously considered in the literature, may be derived upon imposing some convenient constraints. The paper ends with some comparisons with other related work.
763 citations
01 Jan 1973
TL;DR: In this article, the precipitation microstructure varies rapidly with aging temperature and composition, and the influence of composition and aging temperature on the conditions that bring about this compact morphology has been investigated.
Abstract: The precipitation of the γ’ (Ll2) and γ" (DO22) phases has been studied in four alloys Fe-Ni-Cr-Ti-Al-Nb containing a higher Ti + Al/Nb ratio than that of the INCONEL 718 alloy. For these alloys, the precipitation microstructure varies rapidly with aging temperature and composition. Bct γ"particles have always been found to precipitate on γ’ phase. Moreover, by aging three alloys above a critical temperature, a “compact ntorphology” has been observed: cube-shaped γ’ particles coated on their six faces with a shell of γ" precipitate. This microstructure has proved to be very stable on prolonged aging. A thermal stability better than that encountered in nominal INCONEL 718 alloy can thus be achieved. The influence of composition and aging temperature on the conditions that bring about this “compact morphology” has been investigated. A minimal Ti + Al/Nb ratio between 0.9 and 1 has been determined, allowing the “compact morphology” to be obtained.
428 citations
TL;DR: In this paper, a fracture mechanics approach was used to investigate the high strength of hot-pressed Si3N4 powders, and room-temperature flexural strengths, fracture energies, and elastic moduli were determined for material fabricated from α- and β-phase Si3 N4 powder.
Abstract: A fracture mechanics approach was used to investigate the high strength of hot-pressed Si3N4. Room-temperature flexural strengths, fracture energies, and elastic moduli were determined for material fabricated from α- and β-phase Si3N4 powders. When the proper powder preparation technique was used, α-phase powder resulted in a high fracture energy (69,000 ergs/cm2), a high flexural strength (95,000 psi), and an elongated (fiberlike) grain morphology, whereas β-phase powder produced a low fracture energy (16,000 ergs/cm2), a relatively low strength (55,000 psi), and an equiaxed grain morphology. It was hypothesized that the high strength of Si3N4 hot-pressed from α-phase powder results from its high fracture energy, which is attributed to the elongated grains. High-strength Si3N4 has directional properties caused, in part, by the elongated grain structure, which is oriented preferentially with respect to the hot-pressing direction.
274 citations
TL;DR: It was first shown in 1960 that rapid quenching of certain alloys from the melt could form completely extended solid solutions, new metastable crystalline phases, and amorphous solid phases as discussed by the authors.
Abstract: It was first shown in 1960 that rapid quenching of certain alloys from the melt could form completely extended solid solutions, new metastable crystalline phases, and amorphous solid phases. These effects were attributable to the high cooling rates (>or approximately=105 K s-1) from the melt achieved by new techniques of rapidly spreading a few milligrams of liquid alloy into a thin layer in close contact with a good heat conductor (splat cooling). A comprehensive review of developments to data which have resulted from the application of this technique in laboratories throughout the world is presented. It includes an analysis of the range of methods now available for quenching the melt and of present understanding of how they form and quench specimens. The structural features observed as-quenched are then discussed under the divisions of microstructure and extended solid solubility, and of formation of both metastable crystalline and amorphous solid phases. A survey of the response of the as-quenched microstructure to annealing then precedes treatment of the properties and applications of splat-cooled alloys. It is concluded that splat cooling is being established in ever widening fields of study as a tool for controlling structure and properties, and that further applications can be anticipated.
250 citations
TL;DR: In this article, the growth process and the microstructure of very thin W films (80-500 A) deposited by rf sputtering on SiO2 and Si substrates have been observed by transmission electron microscopy (TEM).
Abstract: The growth process and the microstructure of very thin W films (80–500 A) deposited by rf sputtering on SiO2 and Si substrates have been observed by transmission electron microscopy (TEM). The resistivity and stress in these films have been related to the film microstructure, composition, and to the deposition conditions (substrate bias and rf deposition power). Thin W films deposited on silicon dioxide substrates under zero or positive bias have been found to grow in two distinct growth stages. Stage I corresponds to the formation of a thin continuous film (80–100 A thick) of β‐W. The β‐W phase has the A‐15 crystal structure and has been identified as a faulted W3W compound. A small grain size (50–100 A) is characteristic of the β‐W film. Stage II corresponds to the transformation of the β‐W film into a pure α‐W film with the bcc crystal structure. This thermally activated phase transformation takes place in the temperature range 100–200 °C. It is characterized by the growth of α‐W nuclei until complete ...
215 citations
TL;DR: The microstructural transition from amphibolite facies, gneissic country rock, with increasing deformation, to a fine-grained phyllitic mylonite is described in detail in this paper.
193 citations
TL;DR: In this article, the effect of microstructure on the strength-controlling factors, i.e., fracture energy, elastic modulus, and crack size, was investigated in the Si3N4-SiC composite system.
Abstract: The Si3N4-SiC composite system was investigated to better understand the effect of microstructure on the strength-controlling factors, i.e. fracture energy, elastic modulus, and crack size. Silicon carbide dispersions with average particle sizes of 5, 9, and 32 μm were used to form 3 composite series within this system, each containing 0.10, 0.20, 0.30, and 0.40 vol fraction of the dispersed phase. These composites were fabricated by hot-pressing. Fracture energy and strength values were measured for each composite. A linear relation between the elastic modulus of the two phases was assumed. The crack size was calculated for each composite using the appropriate property values. The strength behavior of the 9- and 32-μm series was controlled by the crack size, which, in turn, was controlled by the particle size and volume fraction of the SiC phase. Particle size and volume fraction did not affect the crack size of the 5-μm series, in which strength was controlled by both fracture energy and elastic modulus. Strengths measured at 1400°C and thermal conductivity measurements indicate that several of these composites are promising as high-temperature structural materials.
183 citations
TL;DR: In this paper, the effects of partial phase inversion on dynamic properties of heterogeneous polymer-polymer composites are discussed in terms of equivalent mechanical models and the viscoelastic form of the well-known Kerner equation.
Abstract: The representation and interpretation of dynamic mechanical properties of heterogeneous polymer–polymer composites are discussed in terms of equivalent mechanical models and the viscoelastic form of the well-known Kerner equation. Model parameters calculated from dispersed phase volume fraction and matrix Poisson's ratio (using the Kerner equation) are in fairly good agreement with experimental values for systems comprising soft inclusions in a hard matrix. The effects of partial phase inversion on dynamic properties are discussed in terms of an extension of the Kerner equation. Model calculations indicate that the in-phase component of the complex modulus depends primarily on dispersed phase volume concentration, while the out-of-phase component depends on both the concentration and the morphology of the dispersed phase. Although substantial information about the microstructure of polymer–polymer composites can in principle be deduced from dynamic measurements, quantitative correlation between dynamic properties and use properties such as impact strength (which may have a quite different dependence on structural parameters) is probably fortuitous.
151 citations
TL;DR: In this paper, the phase transition from an amorphous material to a crystalline α-phase occurring at 1200°C for >4 h and/or 1300° to 1400°c for 2 h was observed.
Abstract: Thermal decomposition of silicon diimide, Si(NH)2, in vacuum resulted in very-high-purity, fine-particle-size, amorphous Si3N4 powders. The amorphous powder was isothermally aged at 50° to 100° intervals from 1000° to 1500°C for phase identification. Examination of ir spectra and X-ray diffraction patterns indicated a slow and gradual transition from an amorphous material to a crystalline α-phase occurring at 1200°C for >4 h and/or 1300° to 1400°C for 2 h. As the temperature was increased to ≥1450°C for 2 h, the crystalline β-phase was observed. Phase nucleation and crystallite morphology in this system were studied by electron microscopy and electron diffraction combined with TG as functions of temperature for the inorganic polymer starting materials. Powders prepared in this manner with 4 wt% Mg3N2 added as a sintering aid were hot-pressed to high-density fine-grained bodies with uniform microstructures. The optimum hot-pressing condition was 1650°C for 1 h. Silicon concentration steadily increased as the hot-pressing temperature or time was increased. A method for chemical etching for high-density fine-grained Si3N4 is described. Electrical measurements between room temperature and ∼500°C indicated dielectric constant and tan δ values of 8.3±0.03 and 0.65±0.05×10−2, respectively.
130 citations
Patent•
08 Aug 1973TL;DR: Very rapid crystallization of eutectic and neareutectical molten mixtures of aluminum oxide and zirconium oxide, followed by crushing of the solidified melt, results in abrasive grits of very high strength combined with highly desirable microfracture properties as mentioned in this paper.
Abstract: Very rapid crystallization of eutectic and neareutectic molten mixtures of aluminum oxide and zirconium oxide, followed by crushing of the solidified melt, results in abrasive grits of very high strength combined with highly desirable microfracture properties. The zirconium oxide in the material is in the form of rods (or platelets) which, on the average, are less than 3000 angstroms in diameter, and preferably at least 25%, by weight, of the zirconium oxide is in the tetragonal crystal form. The solidified melt is made up of cells or colonies typically 40 microns or less across their width. Groups of cells having identical orientation of microstructure form grains which typically include from 2 to 100 or more cells or colonies. In crushing, the material fractures along grain boundaries and cell boundaries. Grinding improvement in excess of 100% of prior art standards is shown in tests of coated abrasive products employing the crushed abrasive material in typical applications and substantial improvement in bonded abrasive products.
124 citations
Patent•
30 Mar 1973
TL;DR: In this article, the carbonate skeletal material of marine life was converted into a phosphate skeletal material with a microstructure substantially similar to or corresponding to the micro-structure of carbonate source material by subjecting the skeletal material to hydrothermal chemical exchange with a phosphate.
Abstract: Synthetic material having a microstructure substantially corresponding to the microstructure of porous carbonate skeletal material of marine life and made up of hydroxyapatite or whitlockite is useful as a biomaterial. These synthetic materials are made by converting porous carbonate skeletal material of marine life into a phosphate skeletal material possessing a microstructure substantially the same as or corresponding to the microstructure of the carbonate skeletal source material by subjecting the carbonate skeletal material to hydrothermal chemical exchange with a phosphate.
TL;DR: In this paper, the distribution of impurities and inclusions, phases and dislocation structures in two grades of hot-pressed Si3N4 were investigated by means of replica and thin foil transmission microscopy, and by X-ray diffraction, microprobe and Auger analyses.
Abstract: Grain morphology, distribution of impurities and inclusions, phases and dislocation structures in two grades of hot-pressed Si3N4 were investigated by means of replica and thin foil transmission microscopy, and by X-ray diffraction, microprobe and Auger analyses. High concentrations of impurities, specifically Ca, were detected at the grain boundaries. Fe-W-Si particles were seen within the grain. Non-densified Si3N4 inclusions were found to be detrimental to the strength. Possible correlations among strength, densification data and distribution of elements and phases are discussed.
TL;DR: The various microstructures obtained by the low temperature (C 2 H 2 C 6 H 6 molar ratio) are significantly affected by the type of microstructure.
TL;DR: The boundaries of the homogeneity regions of the phases SmCo 5, GdCo 5 and Gd 2 Co 17 have been determined by microscopic investigation as discussed by the authors, showing that at elevated temperatures the cohesiveness region of these phases extends to the Co-rich and Co-deficient side.
Abstract: The boundaries of the homogeneity regions of the phases SmCo 5 , GdCo 5 and Gd 2 Co 17 have been determined by microscopic investigation. At elevated temperatures the homogeneity region of the phases SmCo 5 and GdCo 5 extends to the Co-rich as well as to the Co-deficient side whereas the phases Gd 2 Co 17 and Sm 2 Co 17 show almost no Co solubility. A tentative diagram is presented for the phase relationships involved in the transition between the two allotropic forms of Gd 2 Co 17 . The occurrence of various types of microstructures in as-cast and annealed RCo 5 samples is explained in terms of the peculiar shape of the solvus of the RCo 5 homogeneity regions at high temperatures.
TL;DR: In this article, the effect of mixing between clouds and their clear air environment has been investigated and it was shown that mixing broadens the spectrum only slightly, while the mean droplet size and total concentration are reduced.
Abstract: Calculations have been made of the effect on the droplet size distribution of mixing between a cloudy parcel and its clear air environment, with attention being concentrated on the first few hundred meters above cloud base where condensation is the dominant process. If the environment is nucleus-free, we conclude that mixing broadens the spectrum only slightly, while the mean droplet size and total concentration are reduced. If the environment contains nuclei which are activated to produce droplets after mixing has occurred, the spectrum is broadened considerably but in a way which 15 not observed in natural clouds. In natural clouds we find that the dispersion of the droplet size distribution is independent of the amount of mixing that has taken place if, as a measure of the mixing, we use the ratio of the observed liquid water content to its adiabatic value at the position of the droplet sample. Thus, from both theory and observation we must conclude that simple mixing between cloud and environ...
TL;DR: In this paper, the nonlinear volt-ampere characteristics and small-signal ac capacitance and resistance of sintered ZnO containing 0.5 mol% Bi2O3 were measured.
Abstract: The nonlinear volt-ampere characteristics and small-signal ac capacitance and resistance of sintered ZnO containing 0.5 mol% Bi2O3 were measured. Many of the electrical properties are related directly to the microstructure, which consists of conductive ZnO grains separated by a continuous amorphous Bl2O3, phase. The origin of the nonlinear conduction in the intergranular phase was confirmed by experiments with evaporated thin films. The proposed conduction mechanism in varistors containing ZnO and Bi2O3 is a combination of hopping and tunneling in the amorphous phase.
TL;DR: The microstructure of cellulose acetate reverse osmosis membranes has been elucidated with the aid of scanning and transmission electron microscopy in this paper, showing that the gel morphology of each of these layers originates in its sol precursors within the nascent membrane which manage to survive the sol gel transition intact.
Abstract: The microstructure of cellulose acetate reverse osmosis membranes which have been prepared by the Kesting dry process has been elucidated with the aid of scanning and transmission electron microscopy. The dry-RO membranes consist of three layers: skin, transition layer, and substructure. The gel morphology of each of these layers originates in its sol precursors within the nascent membrane which manage to survive the sol gel transition intact. The dense skin layer is composed of aggregates of tiny, slightly ellipsoidal nodules which are believed to be paracrystalline in nature. Immediately beneath the skin lies the transition layer, a narrow band of intermediate density consisting of widely separated closed cells. Below the latter lies the porous substructure which is composed of micrometer-sized, open-celled voids. Because of the size of their substructural voids, dry-RO membranes are able to reversibly undergo wet–dry cycling without densification and loss of permeability.
01 Dec 1973
TL;DR: In this paper, the phenomenological martensite theory is applied to the β 1 to β 1 martensitic transformation in Cu-Al and the resulting microstructure is verified with X-ray pole figures, which are combined with a single surface trace analysis based on the use of polarized light.
Abstract: The phenomenological martensite theory is applied to the β1 to β1 martensitic transformation in Cu-Al. Crystallographic and morphological aspects of the resulting martensitic microstructure are discussed and verified with X-ray pole figures, which are combined with a single surface trace analysis based on the use of polarized light. From the analysis of the orientation of any single martensite plate related to that of one or more neighboring plates, it can be proved that the martensite microstructure in each former β-grain is composed of at most six self-accommodating martensite plate groups, each of which consists of four different martensite plate variants.
TL;DR: In this article, the microstructure of crazes formed in solvent-cast thin films has been studied by transmission electron microscopy, and the results have been compared with the results derived from the examination of replicas obtained from the fracture surfaces of bulk specimens.
Abstract: The microstructure of crazes formed in solvent-cast thin films have been studied by transmission electron microscopy. The results have been compared with the microstructure of crazes determined from the examination of replicas obtained from the fracture surfaces of bulk specimens. The structure of crazes formed in thin films and in the bulk have been shown to be similar with the exception that much finer fibril structures are observed in thin films at large deformations. A model of the microstructure of a craze is presented.
TL;DR: In this article, it was found that similar densities of dislocations unbound in sub-boundaries exist in various metals in steady-state creep at the same value of the ratio of applied stress to elastic modulus.
Abstract: Some recent data obtained by investigating dislocation substructure formed in high-temperature creep of several metals are summarized, and some substructural aspects of both steady-state and primary creep are discussed on the basis of the data analysis. It is found that similar densities of dislocations unbound in sub-boundaries (free dislocations), ρ, exist in various metals in steady-state creep at the same value of the ratio of applied stress to elastic modulus. In steady state the mean subgrain diameter is proportional to the reciprocal of the square root of the total dislocation density ρc=ρ+ρSB ρSB being the density of dislocations forming sub-boundaries. Recovery in steady-state creep most probably takes place almost exclusively by annihilation of free dislocations and not by the entry of these dislocations into the sub-boundaries. The total dislocation density was found to increase in the course of primary creep. Most of the dislocations generated go to build the sub-boundaries as the den...
TL;DR: The defect structure of crustally deformed orthopyroxenes from a dunite, a peridotite, and a pyroxenite are characterized and their defect structures are compared with that of an orthopyronene of a lherzolite from a volcanic xenolith as mentioned in this paper.
Abstract: The defect structure of crustally deformed orthopyroxenes from a dunite, a peridotite, and a pyroxenite are characterized and their defect structures are compared with that of an orthopyroxene of a lherzolite from a volcanic xenolith. The microstructures contained isolated unit dislocations, isolated stacking faults, and Ca-rich, clinopyroxene lamellae. The isolated dislocations have Burgers vectors, b, which were predominantly [001]. The stacking faults have a displacement vector R =1/4[001]. A lamellae consisted of a 1/4 μ wide Ca-rich region bounded by complex dislocation arrays. These lamellae are usually 100 μ or more in length and are nearly parallel to the (100) in the matrix. The dislocations in the boundary regions are spaced about 500 A apart. The lherzolite orthopyroxenes were nearly free of isolated defects, in comparison to the other samples. Annealing at 1390° C for 1 hr produced no detectable recovery of the isolated defects in the orthopyroxene substructure.
TL;DR: The room-temperature fracture behavior of partially stabilized ZrO3 (PSZ) in the system CaO-ZrO2 was investigated in this paper, where fracture energy was measured using standard single-edge crack and work-of-fracture techniques.
Abstract: The room-temperature fracture behavior of partially stabilized ZrO3 (PSZ) in the system CaO-ZrO2 was investigated Fracture energy was measured using standard single-edge-crack and work-of-fracture techniques Attempts were made to relate the fracture toughness parameters to the microstructure of the material Stable crack propagation was always observed; a model is proposed to explain these observations on the basis of the formation of a microcrack zone at the tip of a propagating crack The occurrence of initial stable crack propagation is explained in terms of an increase in microcrack zone size The possibility that crack stability results from testing geometry superimposed on the microcracking stability is also discussed
TL;DR: In this article, a comprehensive examination of the early hydration and microstructural development in tricalcium silicate pastes has been performed using scanning electron microscopy using both fracture surfaces and randomly sawn surfaces that have been polished and etched.
TL;DR: In this article, annealed samples of both high-purity and Mg-doped Al2O3 sintered in H2, N2, O2, or vacuum were analyzed at 1650° to 1850°C for times up to 64 h.
Abstract: Samples of both high-purity and Mg-doped Al2O3 sintered in H2, N2, O2, or vacuum were annealed at 1650° to 1850°C for times up to 64 h. In pore-free systems, grain growth is limited by the mobility of Mg-rich second-phase inclusions; in samples annealed in H2, grain growth is limited by pore dragging with a transition toward limitation by solid-inclusion dragging at high dopant levels; in samples annealed in N2 and O2, grain growth is characterized by a transition from an “anchoring effect” of the pores toward a combination of pore dragging by and unpinning from the grain boundaries. Time-dependence of grain growth is insufficient to determine the mechanisms and provide an adequate foundation for model-based calculations. Observations of microstructure and its change with time, together with the rate of grain growth as a function of composition, allow elimination of alternate hypotheses and determination of the process which controls the rate of grain growth and change in pore size.
TL;DR: The precipitates responsible for magnetic age hardening of a Co 3.8 Cu 0.9 Fe 0.5 Ce alloy have been directly observed by transmission electron microscopy as discussed by the authors.
Abstract: The precipitates responsible for magnetic age hardening of a Co 3.8 Cu 0.9 Fe 0.5 Ce alloy have been directly observed by transmission electron microscopy. The precipitates are coherent, plate shaped disks which possess the rhombohedral Co 17 Ce 2 structure. They form in a [001] plate normal orientation and cluster in staggered rows at \sim 30\deg from the [001] axis. The development of precipitate microstructure has been examined in quenched, optimally aged, and overaged alloys. Direct evidence for interaction between the precipitate particles and magnetic domain walls has also been obtained. Among the recently developed Co 5 R based permanent magnets, the Cu containing alloys developed by Nesbitt et al. are of particular interest. These alloys are age hardenable; i.e., their magnetic properties may be improved and controlled by heat treatment. Previous work has revealed that their high coercivities may be attributed to the pinning of domain walls rather than to the nucleation of reverse domains. This report contains a description of some results obtained during an investigation of the alloy structures by transmission electron microscopy. We present direct evidence for the existence of coherent precipitates as well as for the existence of a pinning interaction between magnetic domain walls and the precipitate particles.
TL;DR: In this paper, the capability of the electron beam evaporation technique for producing thin W films having properties suitable for application as first-level metallization in refractory MOS (RMOS) devices was investigated.
Abstract: We have investigated the capability of the electron beam evaporation technique for producing thin W films having properties suitable for application as first-level metallization in refractory MOS (RMOS) devices. The apparatus consisted of a sputter-ion pumped 18-in. diam UHV station, 6-kW e gun, and a quartz crystal rate monitor. The evaporation process employs low background pressures (1−3×10−7 Torr), substrate heating (200–700 °C), a preevaporation step, and evaporation at rates of 100–500 A/min. Maximum throughput is 16 1(14)-in. diam silicon slices per run. Using substrate temperatures of 500–700 °C, we have been able to produce mechanically stable, adherent films having a resistivity of 7–8 μΩ cm and a sheet resistance of ∼ 0.08 Ω/□ (for 9000-A film). “Cold”-deposited films (> 1000 A thick) having a high resistivity of 40–50 μΩ cm can be annealed at 1000 °C to resistivity of 10–15 μΩ cm. The films are single-phase bcc W with a small grain size of 0.1–0.2 μ. Low resistivity films (deposited above 550 °C) are associated with a large degree of microstructural perfection, and have small tensile stresses (3−7×109dyn cm−2). The films possess, excellent high-resolution etchability, and were found to be compatible with MOS structures provided care is exercised during the deposition.
TL;DR: In this paper, the fracture toughness of low alloy quenched and tempered steels with yield strengths over 200,000 psi can be improved by microstructural control by as much as 70 per cent.
01 Aug 1973
TL;DR: In this article, a series of Zr−Ti alloys has been studied by transmission electron microscopy and a transition in morphology and substructure was observed with increasing additions of titanium.
Abstract: Martensitic transformation in a series of Zr−Ti alloys has been studied by transmission electron microscopy. A transition in morphology and substructure was observed with increasing additions of titanium. The 5 wt pct Ti alloy was found to be predominantly dislocated lath martensite while the 10 wt pct Ti alloy showed mainly a twinned plate morphology. Twins within the martensite plates could be classified into two categories, namely, thick\(\{ 10\overline 1 1\} \) twins and thin twins mainly on\(\{ 10\overline 1 1\} \) planes and, to a lesser extent, on\(\{ 11\overline 2 2\} \) and\(\{ 11\overline 2 1\} \) planes. In the case of the thick\(\{ 10\overline 1 1\} \) twins, the specific variant of the twin plane was always found to correspond to a plane of the {110}bcc type, which is a mirror plane in the parent bcc crystal. When the specific variant of the composition plane was not parallel to a mirror plane, the twins were observed to be very thin. Evidence of slip within individual twin bands pointed to the operation of a multiple shear inhomogeneous deformation. Observations concerning\(\{ 10\overline 1 1\} \) deformation twins due to impingement effect are also discussed in this paper.