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Showing papers on "Microstructure published in 1975"


Journal ArticleDOI
TL;DR: In this paper, the microstructure of the strongly deformed compound wires as functions of the degree of deformation and the fibre diameter were discussed. But the authors did not consider the effect of the diameter of the fibres.

167 citations


Journal ArticleDOI
TL;DR: The microstructure of a complex multicomponent varistor ceramic based on ZnO with small additions of antimony, bismuth, cobalt, manganese, and tin oxides has been elucidated using a variety of structural techniques as mentioned in this paper.
Abstract: The microstructure of a complex multicomponent varistor ceramic based on ZnO with small additions of antimony, bismuth, cobalt, manganese, and tin oxides has been elucidated using a variety of structural techniques. Three crystalline phases are found to coexist in the sintered material. The bulk phase consists of a polycrystalline matrix of ZnO doped with Co(II). The ZnO grains are separated from one another by a Bi2Zn4/3Sb2/3O6 pyrochlore phase which forms a three−dimensional threadlike network, indicative of a liquid phase at high temperatures. A Zn(Zn4/3Sb2/3)O4 spinel constitutes the third phase and forms well−faceted octahedral crystals located frequently at grain boundaries between the ZnO and occasionally within the grains. This phase acts as a grain growth moderator for ZnO by anchoring the boundaries during sintering, but plays no role in the nonlinear characteristic of the varistor. A quasiequilibrium between the pyrochlore and spinel has been established such that formation of the spinel is favored at high temperatures. The over−all varistor microstructure may be described as a three−dimensional series−parallel network of ZnO−pyrochlore junctions.

158 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of heat treatment on the microstructure of Li2O-Al2O3·SiO2 glass-ceramics which contain crystals of either Li2SiO3, Li 2Si2O5, or both was investigated quantitatively.
Abstract: The effect of heat treatment on the microstructure of Li2O-Al2O3·SiO2 glass-ceramics which contain crystals of either Li2SiO3, Li2Si2O5, or both was investigated quantitatively. Strength determinations for abraded rods were correlated with heat treatment on the basis of both size and distribution of crystals and the type and amount of crystal phases present. The presence of Li2Si2O5 crystals enhanced the strength, whereas the presence of Li2SiO3 crystals did not change the strength of the abraded parent glass. The interrelation between strength and microstructure is discussed.

148 citations



Journal ArticleDOI
TL;DR: In this article, the effect of microstructure on plane stress and plane strain fracture toughness is considered in detail together with strength, fatigue behavior and corrosion resistance, and it is concluded that second phase particles in all size ranges can influence toughness.
Abstract: With the advent of linear elastic fracture mechanics, the detailed effects of processing and microstructure on toughness can be evaluated. The effect of microstructure on plane stress and plane strain fracture toughness is considered in detail together with strength, fatigue behavior and corrosion resistance. It is concluded that second phase particles in all size ranges can influence toughness. Increasing the size and amount of particles or decreasing precipitate coherency all lead to decreases in toughness. Grain structure is also shown to play a prominent role in determining plane stress fracture toughness ; at a given strength level, a fibrous grain structure and the prevention of recrystallization are desirable. The ability to influence fatigue crack propagation by control of processing is more remote though relatively little systematic work has been carried out in this field. Thermomechanical processing is considered to offer another possible route to achieving a desirable balance of toughness, strength and corrosion resistance.

90 citations


Journal ArticleDOI
TL;DR: In this article, the relationship between the austenitizing temperature, the quenching medium, and the plane strain fracture toughness have been investigated for the following quenched and tempered low alloy commercial steels: 4130, 4330, 4140, 4340, 300-M and 3140.

58 citations



Journal ArticleDOI
TL;DR: In this article, the elastic modulus is strain-dependent and the ultimate tensile strength increases with decreasing crystal size, which corresponds to exceptionally high per-chain properties, nearly as high as that of diamond.
Abstract: The mechanical properties (Young's modulus, ultimate tensile strength, deformation processes) of extended-chain polydiacetylene crystals are investigated. The properties observed are similar to those of metal and ceramic whiskers. The elastic modulus is strain-dependent and the ultimate tensile strength increases with decreasing crystal size. The maximum tensile strength observed was 1700 Nmm−2. The ultimate tensile strength seems to be controlled by the presence of a small number of defects near the surface at which fracture nucleates. Irreversible deformation of the crystals was observed to occur by crack propagation normal and parallel to the direction of the macromolecules. The observed mechanical behavior corresponds to exceptionally high per-chain properties. The per-chain modulus obtained for these crystals is nearly as high as that of diamond. A chain-aligned polyethylene fiber with the same per-chain mechanical properties would have an ultimate strength as high as 0.9 × 104 Nmm−2.

43 citations


Journal ArticleDOI
TL;DR: The correlation between microstructure and hardness of dental gold alloy, Au-35.7 at.% Cu-11.2 at% Ag, was studied by electron microscopy as discussed by the authors, showing that the agehardening peak was due to the formation of plate-like AuCu I on the matrix {100} planes.
Abstract: The correlation between microstructure and hardness of dental gold alloy, Au-35.7 at.% Cu-11.2 at.% Ag, was studied by electron microscopy. The age-hardening peak was due to the formation of plate-like AuCu I on the matrix {100} planes. The microstructure at this stage showed a striation contrast, being parallel to the 〈111〉 directions on the (110) plane, as found in the AuCu alloy. The structure of the final state was identified as AuCu I-type ordered platelets which had the c -axis distributed in the three cube directions and had the [011] twin relation, although relatively higher hardness was maintained at the later stage of ageing.

42 citations


Journal ArticleDOI
J. P. Lyle1, W. S. Cebulak1
TL;DR: In this paper, high strength products made from atomized Al-Zn-Mg-Cu-Co alloy powders have good combinations of strength, ductility, resistance to stress-corrosion cracking and fracture toughness.
Abstract: High-strength products made from atomized Al-Zn-Mg-Cu-Co alloy powders have good combinations of strength, ductility, resistance to stress-corrosion cracking and fracture toughness. Powder Metallurgy (PJM) methods produce fine metallurgical structures and compositions which cannot be produced by Ingot Metallurgy (IJM) methods.

38 citations


Journal ArticleDOI
TL;DR: In this article, the influence of heat treatment on the microstructure of a Ni-45.5 wt pct W directionally solidified eutectic composite has been studied.
Abstract: The influence of heat treatment on the microstructure of a Ni-45.5 wt pct W directionally solidified eutectic composite has been studied. Four types of microstructural conditions have been examined using light and thin foil electron microscopy techniques. The as-grown composite consists of W fibers in a matrix which contains some WNi4 precipitates. Quenching the composite from above the peritectoid temperature results in W fibers in a Ni-W solid solution matrix. Subsequent aging results in precipitation of coherent WNi4. Long time aging at temperatures just under the peritectoid temperature promotes the peritectoid reaction leading to envelopment of the W fibers by a layer of WNi4. The envelopment reaction is accompanied by a change from faceted to round fiber morphology. The presence of W fibers in the Ni-W solid solution influences aging in two ways when compared to a solid solution alloy. First, the fiber/matrix interfaces act as dislocation sources on quenching; these dislocations are absorbed into the WNi4 precipitate/matrix interfaces leading to early loss of coherency. Second, the WNi4 precipitates undergo a preferential coarsening due to elastic interaction between the fibers and the WNi4 precipitates; this leads to a mosaic structure, the occurrence of which is uniquely dependent on the presence of W fibers.

Journal ArticleDOI
TL;DR: In this article, a mechanism involving epitaxial deposition of chain segments onto growing lamellae is concluded to be responsible for formation of the bimodal crystal texture in flow-crystallized material.
Abstract: Electron microscopy, selected area electron diffraction, X-ray diffraction, and dynamic-mechanical testing have been used to study flow-crystallized and hot drawn isotactic polypropylene. As a result of these investigations, it was found that bimodal crystal textures can apparently be formed by at least two different treatments, but the corresponding morphologies are completely different. Flow-induced crystallization was observed to result in a microstructure of lamellae oriented perpendicular to the flow direction, while hot drawing of polypropylene films above a critical temperature produced a morphology of microfibrils lying parallel to the draw direction. Below this critical temperature, drawing produced a fibrillar morphology having only a typical unimodal fibre texture. As a result of information obtained here, a mechanism involving epitaxial deposition of chain segments onto growing lamellae is concluded to be responsible for formation of the bimodal crystal texture in flow-crystallized material.

Journal ArticleDOI
TL;DR: In this paper, the semi-crystalline polymer TPX has been injection moulded into standard tensile bars using a range of barrel temperatures, mould temperatures and injection pressures, and three-point bend tests on the injection molded bars indicated that a ductile-to-brittle transition in failure mode could be induced by changing the moulding conditions, and that this change could be correlated with microstructural and dimensional changes.
Abstract: The semi-crystalline polymer TPX has been injection moulded into standard tensile bars using a range of barrel temperatures, mould temperatures and injection pressures. Acid etching, microhardness testing and selected volume X-ray pole figures were used to characterize the changes in microstructure and crystalline texture which occurred throughout the range of mouldings. A strong correlation was shown to exist between microstructure and crystalline texture and processing conditions. Three-point bend tests on the injection moulded bars indicated that a ductile-to-brittle transition in failure mode could be induced by changing the moulding conditions, and that this change could be correlated with microstructural and dimensional changes.

Journal ArticleDOI
TL;DR: In this article, the microstructure of dc-triode compound sputtered ZnO films was investigated using the analytical tools of scanning electron microscopy (SEM), reflection electron diffraction (RED), and x-ray diffraction(XRD).
Abstract: Zinc oxide, vacuum deposited as a crystalline aggregate with preferential orientation of its fiber grains, has been used extensively as a film transducer for generating micro‐acoustic waves. The orientation and size of the crystallite grains have a pronounced effect on the film’s electromechanical properties. The microstructure of dc‐triode compound sputtered ZnO films was investigated using the analytical tools of scanning electron microscopy (SEM), reflection electron diffraction (RED), and x‐ray diffraction (XRD). The ZnO films investigated had been deposited on fused quartz and oxidized silicon having surface interdigital electrode arrays from which the acoustic surface‐wave properties of coupling efficiency, velocity, and propagation loss had been determined. Optically clear films having electromechanical and propagation properties approaching those of single‐crystal zinc‐oxide layers were found to have a smooth surface, a dense, amorphous‐like vertical structure, an average crystallite size estimate...

Book ChapterDOI
01 Jan 1975
TL;DR: In this paper, it is shown that most of the significant features of the structure of a material are of a "microscopic" size, that is, from a few tens of microns down to atomic dimensions.
Abstract: Materials science is totally concerned with the structure of materials, with the understanding and control of structure and with the prediction and understanding of its ultimate consequences—the macroscopic properties of matter. Materials scientists, therefore, use extensively those techniques that have been developed to investigate the structure of matter at all levels from the macroscopic down to the atomic. It is commonly found that most of the significant features of the structure of a material are of a ‘microscopic’ size, that is, from a few tens of microns down to atomic dimensions. Techniques for investigating structure at this level may be classified into methods based upon the analysis of diffraction patterns, which give information averaged from a relatively large sample, and imaging methods, which give detailed information about a small region. For very many applications the imaging methods are more useful, since the local arrangement of the microstructure is often extremely important. A few examples will make this clear. Plastic flow in a crystalline solid is controlled by the generation and movement of dislocations and their interaction with other microstructural features. A solid-state precipitate may greatly improve the mechanical properties of a material if it is finely dispersed within the grains, but can cause catastrophic brittleness if it collects at a grain boundary.

Journal ArticleDOI
TL;DR: In this article, the quality of silicon nitride films was found to be strongly dependent on the discharge nitrogen pressure, and the degradation of film properties accompanying an increase in the nitrogen discharge pressure was correlated with the presence of microvoids, revealed by transmission electron microscopy.
Abstract: The quality of silicon nitride films deposited by rf reactive sputtering of silicon in a nitrogen discharge is found to be strongly dependent on the discharge nitrogen pressure. For a given substrate to target spacing there is a "critical" sputtering pressure which, if exceeded, results in deposition of films with noticeably inferior properties. The properties of silicon nitride films deposited both above and below this critical pressure are compared. The degradation of film properties accompanying an increase in the nitrogen discharge pressure is correlated with the presence of microvoids (~50A), revealed by transmission electron microscopy. It is suggested that the microvoids result from a reduction in the reemission of deposited material as the discharge pressure is increased.

Journal ArticleDOI
TL;DR: In this article, the effect of grain size on unit-cell dimensions and dielectric properties has been studied in ceramic lanthana-substituted leadtitanate and lead-itanate-zirconate mixed crystals of the general composition Pb1−αxLaxZryTi1−yO3+x(1.5−α).


Book ChapterDOI
J. G. J. Peelen1
01 Jan 1975
TL;DR: The effect of dopants on the sintering behavior of Al2O3 has been investigated in this paper, showing that the addition of 0.25 wt % MgO inhibits discontinuous grain growth and allows nearly theoretical densities to be achieved.
Abstract: Small amounts of additives can have a great influence on the sintering of ceramic powders. The most extensively studied example is, without doubt, the effect of dopants especially MgO, on the sintering behaviour of Al2O3. In spite of all these studies many questions are still unsolved since Coble1 reported that the addition of 0.25 wt % MgO inhibits discontinuous grain growth and allows nearly theoretical densities to be achieved.

Journal ArticleDOI
TL;DR: The crystallographic structure and microstructure of thin Cd3As2 films, formed by vacuum evaporation onto mica substrates, have been investigated as functions of the deposition rate and substrate temperature as mentioned in this paper.


Journal ArticleDOI
TL;DR: In this paper, a crack-free Co-Mo coatings containing 12% to 18% molybdenum were electroplated on metal substrates from an aqueous citrate complex bath containing sodium molydate and a cobalt salt.

Journal ArticleDOI
TL;DR: In this paper, the steady-state creep behavior of reaction-bonded silicon nitride, prepared by slip casting and injection molding, was examined in 4-point bending with stresses ranging from 10,000 to 20,000 psi at temperatures from 1200° to 1450°C.
Abstract: The steady-state creep behavior of reaction-bonded silicon nitride, prepared by slip casting and injection molding, was examined in 4point bending with stresses ranging from 10,000 to 20,000 psi at temperatures from 1200° to 1450°C. Creep rates were proportional to the 1.4 power of the stress. The creep process exhibited an activation energy of 130±5 kcal/mol. The microstructure of deformed specimens, which was revealed by transmission and scanning electron microscopy, contained triple-point voids suggesting that the rate-controlling mechanism of creep is grain-boundary sliding.

Journal ArticleDOI
TL;DR: In this paper, an extensive study of the interrelation of heat treatment, microstructure, creep strength, rupture strength and rupture ductility, and fracture characteristics has been made in commercially produced 0·5Cr-0·5Mo 0·25V and 1Cr-1 Mo 0·15V steels tested at 550°C for times up to >20000h.
Abstract: The performance of Cr-Mo-V steels, as widely used for steam pipe work, turbine rotors and casings, and associated bolts in steam power generating plant, may be limited by a susceptibility to failure at low ductility, especially when heat treated to high strength levels. To investigate the ductility in creep conditions of such steels, an extensive study of the interrelation of heat treatment, microstructure, creep strength, rupture strength, rupture ductility, and fracture characteristics has been made in commercially produced 0·5Cr-0·5Mo-0·25V and 1Cr-1 Mo-0·25V steels tested at 550°C for times up to >20000h. The results show that the rupture strength and ductility can be varied widely by changing the austenitizing temperature and the rate of cooling therefrom, and that a heat treatment at a high temperature (1300°C), given to simulate the microstructure in the vicinity of a weld, can produce very low creep-rupture ductility (<1%). Low ductility in these steels is associated with an intergranular ...

Journal ArticleDOI
TL;DR: In this article, the directionality of properties in α and α + β titanium alloys results primarily from the elastic and plastic anisotropy of the hexagonal lattice a-phase.
Abstract: Mechanical properties are influenced by direction of testing with respect to wrought microstructure. In aluminium alloys the properties most sensitive to direction are ductility, fracture toughness, and stress corrosion and this can be attributed to the well developed mechanical fibring that exists in these alloys. Crystallographic textures are developed, particularly in extrusions, and some useful enhancement of strength is achieved in the longitudinal direction. Nevertheless, from a general viewpoint mechanical fib ring produces the predominant effects. Directionality of properties in α and α + β titanium alloys results primarily from the elastic and plastic anisotropy of the hexagonal lattice a-phase. Directionality effects are discussed, including those exhibited by the fatigue, tensile, fracture toughness, creep, stress corrosion, and sustained load properties. The important benefit of plastic anisotropy in terms of texture strengthening is highlighted, and it is concluded that optimum proper...

Journal ArticleDOI
TL;DR: In this article, the profile of the 002 diffraction peak of polyethylene is related to microstructural parameters for the [001] direction, including mean crystal thickness, distribution of thicknesses, shape function and the degree of paracrystalline disorder in the lattice.
Abstract: The profile of the 002 diffraction peak of polyethylene is related to microstructural parameters for the [001] direction. The parameters considered are the mean crystal thickness, distribution of thicknesses, shape function and the degree of paracrystalline disorder in the lattice.

Journal ArticleDOI
TL;DR: In this paper, a study was made on the formation of "fir-tree" structure during casting of Al-Fe alloys, and the results obtained are summarized as follows: 1) Al3Fe, Al6Fe and AlmFe (a body-centered tetragonal al-Fe phase8)) were identified as secondary constituents.
Abstract: A study was made on the formation of 'fir-tree' structure during D. C. casting of Al-Fe alloys. Al-Fe alloys containing 0.58%Fe and less than 0.01%Si were unidirectionally solidified. The alloys were also D. C. cast. The cooling rate during unidirectional solidification was measured by thermal analysis, while the cooling rate during D. C. casting was estimated through measurements of the dendrite arm spacing of the ingots. Identification of constituent phases were carried out by optional microscopy, electron microscopy and X-ray diffraction, and some of their chemical properties were discussed.The results obtained are summarized as follows:1) Al3Fe, Al6Fe and AlmFe (a body-centered tetragonal Al-Fe phase8)) were identified as secondary constituents. They were found to be formed in the following ranges of cooling rate:Al3Fe: less than 2°C/secAl6Fe: from 2 to 20°C/secb.c.t.AlmFe: more than 20°C/sec.2) Al3Fe and b.c.t. AlmFe were oxidized during anodizing in 15%H2SO4 solution, while Al6Fe did not undergo oxidation. Al3Fe and b.c.t. AlmFe were etched to appear dark-brown by 0.5%HF solution, while in the case of Al6Fe, only a slightly grey tint was detected.3) The microstructure of the D. C. cast ingots was divided into the four regions corresponding to different sizes of dendrite cells and to different constituent phases. The first, these cond and the third regions were outside the 'fir-tree' structure, while the fourth region was inside. Body-centered tetragonal AlmFe and a small amount of Al3Fe were secondary constituents in the first region which solidified very rapidly. Al3Fe phase existed in the second and third regions which solidified more slowly. Al6Fe phase was an interdendritic phase in the fourth region which solidified fairly fast.4) The cause of formation of 'fir-tree' structure seems to be attributable to the fact that the cooling rate during solidification varies from the surface to the center of D. C. cast ingots. In other words, the cause is likely attributed to macroscopic segregation of different types of intermetallic compounds.

Journal ArticleDOI
TL;DR: In this paper, the authors test a concept of controlling stress corrosion crack propagation in Al-Zn-Mg alloys through the use of minor alloying additions of elements known to retard hydrogen ion recombination.
Abstract: Studies were undertaken to test a concept of controlling stress corrosion crack propagation in Al-Zn-Mg alloys through the use of minor alloying additions of elements known to retard hydrogen ion recombination. Previous work suggested that the recombination of hydrogen ions governs the rate of anodic dissolution and, in turn, the rate of crack propagation in these alloys. Results indicated that the concept was invalid since the minor alloying additions themselves exerted a more profound influence on the grain boundary microstructure. Specifically, the microstructural features of grain boundary particle size and interparticle spacing were found to correlate with stress corrosion susceptibility. Auger electron spectroscope studies also revealed a correlation between the concentration of Zn and Mg within the precipitate-free zone and the susceptibility to cracking.

Journal ArticleDOI
TL;DR: In the absence of radiation the corrosion of quenched, cold worked and aged Zr-2.5 Wt% Nb in 280 C (536 F) pressurized water decreases with increasing aging time and temperature.
Abstract: In the absence of radiation the corrosion of quenched, cold worked and aged Zr-2.5 Wt% Nb in 280 C (536 F) pressurized water decreases with increasing aging time and temperature. Under neu...

Journal ArticleDOI
M. Pinnel1, J. Bennett1
TL;DR: In this article, the effects of varying aging times for temperatures between 885°C and 925°C on an Fe/Co/3% V alloy have been analyzed, and the variations in coercivity, remanence, and microstructure for 2\frac{1}{2} hour aging anneals between 300°c and 1000°c on an Alloy have been determined.
Abstract: The variations in coercivity, remanence, and microstructure for 2\frac{1}{2} hour aging anneals between 300°C and 1000°C on an Fe/Co/3% V alloy have been determined. Additionally, the effects of varying aging times for temperatures between 885°C and 925°C have been analyzed. Hysteresis parameters and optical microstructures were characterized on wire samples which had been either cold worked by stamping or remained undeformed prior to the aging anneals. Results show that the alloy exhibits maximum magnetic hardness in its initial cold worked or undeformed conditions. Aging anneals produce a general decrease in magnetic properties with increasing temperatures to 700°C. However, the deformed material exhibits a secondary maximum for aging temperatures between 590°C and 610°C. For anneals above 800°C magnetic parameters again increase as a two-phased, duplex BCC (α 1 + α 2 ) structure is developed. By varying the aging time for anneals that produce this duplex structure, a level of coercivity comparable to that achieved for a 600°C anneal was attainable. However, a comparable level of remanence and, thus, a similar squareness ratio, could not be produced with the duplex structures developed by aging near 900°C.