Showing papers on "Grain growth published in 1975"
TL;DR: Thor Thornton et al. as discussed by the authors used hollow and post-type cathode sputtering apparatuses at argon pressures of 1 and 30 mTorr to evaluate OFHC copper coatings on copper, tantalum, and stainless steel substrates.
Abstract: Thick [1–10 mil (25.4–254.0 μm)] OFHC copper coatings were deposited on copper, tantalum, and stainless‐steel substrates maintained at temperatures (T) in the 50 °–950 °C range, at rates of from 200 to 18 000 A/min, using primarily hollow and also post‐type cathode sputtering apparatuses at argon pressures of 1 and 30 mTorr. Coating structures were examined by preparing metallographic cross sections. Surface topographies and fracture cross sections were examined by scanning electron microscopy. Crystallographic orientations were determined by x‐ray diffraction. No significant deposition rate influence was found on the low‐temperature structure zones reported previously [J. A. Thornton, J. Vac. Sci. Technol. 11, 666 (1974)] or on the columnar nature of coatings formed at elevated T. Truly equiaxed grain structures were generally not observed with hollow cathodes. Annealing twins were found within the grains for T≳350 °C. Evidence of extensive recrystallization and grain growth was seen for T∠900 °C. Coatin...
405 citations
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
TL;DR: In this paper, the authors used a moving hot zone to increase grain size and aspect ratio in dispersion strengthened nickel-base superalloys made from mechanically alloyed powder, and the relationship between grain aspect ratio and mechanical properties in these materials is discussed.
Abstract: The high temperature strength of dispersion strengthened materials is limited by grain boundary sliding and transverse boundary rupture. These effects are minimized through development of materials with elongated or fibrous grain structures. Thermomechanical processing and grain growth heat treatments are used to develop coarse elongated grain structures in dispersion strengthened nickel-base superalloys made from mechanically alloyed powder. Grain size and aspect ratio are increased by using a moving hot zone to accomplish grain growth. The application of this technique to extruded bar of two nickel-base superalloys, IN-853* (Alloy A) and a developmental alloy (Alloy B) with composition: 15Cr, 4.5A1, 2.5Ti, 2Ta, 3.5Mo, 4W, 0.l5Zr, 0.01B, 1.1Y2O3 is discussed, and the relation between grain aspect ratio and mechanical properties in these materials is presented.
72 citations
TL;DR: In this paper, the oxidation behavior of Ni-20%Cr alloys containing approximately 3 vol.% Y2O3, ThO2, and A12O3 as dispersed particles has been examined in the temperature range 900 to 1200°C in slowly flowing oxygen at 100 Torr.
Abstract: The oxidation behavior of Ni-20%Cr alloys containing approximately 3 vol.% Y2O3, ThO2, and A12O3 as dispersed particles has been examined in the temperature range 900 to 1200° C in slowly flowing oxygen at 100 Torr. The results show that the oxidation behavior of the Y2O3-, ThO2-, Al2O3-, and Ce02-containing alloys is very similar and that some anomalies in the behavior of the ThO2-containing alloy might be explained by the slower rate of chromium diffusion in this coarse-grained alloy. Two Al2O3-containing alloys were studied. One with a relatively coarse dispersoid size behaved in a manner analogous to a dispersion-free Ni-30% Cr alloy at 1100°C. The other alloy contained a dispersion of fine Al2O3 particles and behaved exactly like the Y2O3-containing alloy at 1000 and 1100°C, but at 1200° C oxidized at a faster rate. It has been shown that the adherent scales on dispersion-containing alloys have a stabilized fine grain size, whereas the nonadherent scales on dispersion-free alloys undergo grain growth.
56 citations
TL;DR: In this paper, the pore-solid interface at first decreased slowly, then more rapidly and ultimately linearly with pore volume fraction, as has been reported in other systems, and the area of grain boundary initially increased slowly, as interparticle contacts grew; at aboutVV = 0.15, grain growth set in, and grain boundary area decreased, as the mean grain intercept rapidly increased with densification.
Abstract: Quantitative paths of microstructural change, represented as a variation of topological and metric properties with pore volume fraction, were experimentally determined by applying quantitative microscopy to sequences of samples sintered without compaction from two size fractions of spherical copper powder, and one size fraction of dendritic copper powder. The two spherical size fractions followed paths of microstructural change during sintering that were identical except for a scale factor. The connectivity of the pore network first increased slightly, then decreased, reaching zero at a pore volume fraction (VV) of about 0.08. Isolated pores begin to appear atVV = 0.20, and increased in number. The area of the pore-solid interface at first decreased slowly, then more rapidly and ultimately linearly with pore volume fraction, as has been reported in other systems. Total curvature of pore-solid interface decreased from the positive value characteristic of the loose powder stack to a negative value, passed through a minimum, and increased toward zero as full density is approached. The area of grain boundary initially increased slowly, as interparticle contacts grew; at aboutVV = 0.15, grain growth set in, and the grain boundary area decreased, as the mean grain intercept rapidly increased with densification.
43 citations
TL;DR: In this paper, the effect of substrate temperature on the nucleation and growth of gold films vaporized on a single crystal graphite was studied using transmission electron microscopy and diffraction, and it was shown that the morphology of the gold particles changes with substrate temperature.
41 citations
TL;DR: In this paper, a semi-empirical model for intermediate-stage sintering is developed based on simultaneously occurring volume and grain-boundary diffusion mechanisms of mass transport and explicitly incorporating the effects of grain growth.
Abstract: A semiempirical model for intermediate-stage sintering is developed based on simultaneously occurring volume and grain-boundary diffusion mechanisms of mass transport and explicitly incorporating the effects of grain growth. The sintering equation derived depends strongly on the reduction of pore number density associated with grain growth and is independent of the mechanism of grain growth. The time and temperature dependencies of densification predicted by the equation, which are tested using data for metal and ceramic powders, agree well with observations. The data indicate that grain-boundary diffusion contributes negligibly to densification.
40 citations
TL;DR: The coarsening behavior of two Cu-Ni-Fe alloys has been found to include a discontinuous reaction which originates at larger misorientation grain boundaries as discussed by the authors.
36 citations
TL;DR: In this article, high green density UO2 powder compacts were annealed over a range of temperatures to establish the sintering mechanisms for open and closed porosity, and interconnected porosity was found to sinter at a rate consistent with a volume diffusion process dependent on the instantaneous grain size.
Abstract: High green density UO2 powder compacts were annealed over a range of temperatures to establish the sintering mechanisms for open and closed porosity. During the intermediate stage of sintering the interconnected porosity was found to sinter at a rate consistent with a volume diffusion process dependent on the instantaneous grain size. The apparent activation energy for open pore sintering was significantly higher than that for volume or grain boundary diffusion, this being attributed to systematic differences resulting from the grain growth process. The fraction of closed porosity increased to a maximum with the collapse of the open porosity then decreased during the final stage of sintering.
TL;DR: In field and glasshouse experiments with grain sorghum, results are interpreted as evidence that grain yield is not limited by the storage capacity of the grain, or by the transport system involved in moving material from the stem to the grain.
Abstract: In field and glasshouse experiments with grain sorghum (cv. RS610), the assimilate supply was varied by increasing or decreasing radiation and carbon dioxide supply; the potential grain storage capacity was altered by spikelet removal; and the transport system was reduced by incision of the culm. Plants grown at four population densities in the field were manipulated to increase (by removing neighbouring plants) or decrease (by shading) the supply of photosynthates during grain filling. These treatments affected grain size and thus yield. Removal of some of the spikelets at three-quarter anthesis resulted in a significant increase in the size of those grains remaining at maturity. From anthesis onward, a reduction in the capacity of the transport system in the culm had no significant effect on grain yield. These results are interpreted as evidence that grain yield is not limited by the storage capacity of the grain, or by the transport system involved in moving material from the stem to the grain. Treatments which altered the demand for assimilates by the grain, relative to the supply, did not affect net photosynthesis. Dry matter produced in excess of grain requirements accumulated in other plant parts, including the root. Potential grain size was influenced by interspikelet competition operating within 1 week after three-quarter anthesis. *Part II, Aust. J. Agric. Res., 22: 39-47 (1971).
TL;DR: In this paper, the grain boundary resistivity was measured after annealing at temperatures up to 500 ˚ c and the rate constant of the resistivity recovery was temperature dependent with an activation energy of 1.58 eV.
Abstract: Co films were deposited by electron‐beam evaporation onto oxidized Si wafers. The resistivity was measured after annealing at temperatures up to 500 °C. The resistivity after deposition is about 8 μΩ cm and decreases to the bulk value on annealing. This occurs in two stages: 230–380 °C (stage A) and 410–430 °C (stage B). Stage A is attributed to a decreasing grain boundary scattering owing to grain growth and secondary recrystallization and can be described as a second‐order reaction. The grain size d increases in this temperature interval from about 0.07 to 4 μm. The rate constant of the resistivity recovery is temperature dependent with an activation energy of 1.58 eV which is suggested to be the grain boundary migration energy. A deviation from Matthiessen’s rule is explained as being due to the preferred hcp (001) orientation which is strongly enhanced by annealing. Stage B is attributed to a reduction of the number of dislocations, stacking faults, and twin boundaries. A grain boundary resistivity of...
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.
TL;DR: In this article, the theoretical background, uses and new development of grain-oriented silicon steel with high permeability using A1N as a grain growth inhibitor are discussed, and core loss improvements on actual transformers using high-permeability materials are approximately 10-25% in wound type pole transformers and 5-20% in laminated type large transformers.
Abstract: The effect of the substrate temperatures in a wide range between −150 and 270 °C on the grain size, crystal orientation, Hall mobility, and the carrier concentration of evaporated Te films has been investigated. The grain size and the corresponding Hall mobility were observed to increase remarkably with increasing substrate temperature above 50 °C and with decreasing temperature below 50 °C, contrary to the expectation. The carrier concentration decreased with increasing substrate temperature. The influence of Au nucleation centers on the crystallinity and electronic properties were also investigated. An x−ray diffractometer study indicated c−axis texture to occur with improving grain growth.
TL;DR: In this article, the particle growth characteristics of active MgO in the size range 70-400 A have been studied by the X-ray line broadening technique, where the starting material was a synthetic magnesium hydroxide, which was decomposed and then heat treated under isothermal conditions in the temperature range 400-900°C in air.
TL;DR: In this paper, the effects of composition and processing on microstructure and fracture behavior of Al-Zn-Mg-Cu (7075 type) alloys were investigated.
Patent•
29 Dec 1975
TL;DR: In this article, the process of forming an aluminum-silicon-iron alloy powder is described, sintered and hot-pressed simultaneously with or after sintering, and the alloy powder can contain 4-9% aluminum, 8-11% silicon, and remainder iron.
Abstract: Aluminum-silicon-iron alloys exhibiting an excellent combination of properties are disclosed. The process for preparing these alloys is also disclosed. In this process an aluminum-silicon-iron alloy powder is formed, sintered and hot-pressed simultaneously with or after sintering. The alloy powder can contain 4-9%, by weight, aluminum, 8-11%, by weight, silicon and the remainder iron. Pressures for hot-pressing of at least 1000 psi. and sintering temperatures of at least 1205° C are disclosed. The process can also include the additional step of nitriding the alloy powder prior to sintering. Such nitriding prevents or retards grain growth during sintering and provides increased electrical resistivity and hardness in the end product.
TL;DR: In this article, four MX-type fuels (U, Pu)C, PuC 0.5N0.5, pU)c 0.2N 0.8, and PuN N 0.1N 0.5N 0, were irradiated in helium-bonded pins at heat ratings up to 1300 W/cm.
01 Jan 1975
TL;DR: In this article, the authors replaced the complex geometry of the compact interior by a system of uniform cylindrical pores situated on the edges of polyhedra of uniform size, and the grain growth observed during sintering was interpreted as an increase of the length of the polyhedron's edge with time.
Abstract: Most of our knowledge of the elementary processes occurring during sintering originated from model experiments. However, the study of systems with well defined and uniform geometry cannot furnish sufficient information to describe in some detail the behavior of the whole particle assembly such as a powder compact. Even the kinetics of the first stage of sintering cannot be simply treated by the rates of formation of interfaces between adjacent particles.1, 2, 3 The intermediate stage of sintering which is essentially the shrinkage of a continuous pore phase and the final stage dealing with a discrete pore phase, cannot be represented by simple models, because the Ostwald ripening of the pores is an essential part of the densification process. For this reason the well known Coble4 theory for the intermediate stage of sintering, most recently refined by Beere5, is unsatisfactory. Coble replaced the complex geometry of the compact’s interior by a system of uniform cylindrical pores situated on the edges of polyhedra of uniform size. The grain growth observed during sintering was interpreted as an increase of the length of the polyhedron’s edge with time and the empirical relation for the grain growth was introduced into a differential equation for cylindrical pore shrinkage. In this manner the system of non uniform pores and grains was replaced by one of well defined geometry which reduced the problem to one of the kinetics of shrinkage of an average cylindrical pore in an average geometrical environment. Coble has realized that pore shrinkage and simultaneous increase of their average size, as well as that of the crystalline grains, are mutually interdependent, but within his model he could not formalize these relations.
TL;DR: In this article, aluminum-4 wt.% copper alloy films were prepared by vapor deposition and examined for grain growth in the temperature range 400°-500°C. The results showed that growth occurs in accordance with the empirical equation D = ( Kt ) n.
TL;DR: In this paper, the growth of BeO particles and beryllium grains in hot-pressed blocks have been studied and the size of the particles was found to increase as the aluminum, magnesium and silicon contents were raised.
Abstract: The factors governing the growth of BeO particles and beryllium grains in hot-pressed beryllium block have been studied. The size of BeO particles was found to increase as the aluminum, magnesium and silicon contents were raised. Higher processing temperatures during manufacture also increased the size of the oxide. Silicon doping of the beryllium powder before pressing was found to be a particularly effective way of increasing BeO particle size. The pressure-temperature cycle employed during hot pressing was also found to affect the oxide morphology. Cycles that produced full density at the lowest temperature minimized the extent of oxide agglomeration. Diffusion of aluminum and a combination of aluminum, silicon and iron into high purity beryllium at 1366 K produced a grain boundary liquid phase which resulted in an accelerated grain growth rate and BeO agglomeration.
TL;DR: In this article, a thermal cycling technique for grain refinement of In alloys from 400 μm to less than 10 μm has been developed, which consists of annealing in the α phase field of a fully precipitated alloy.
TL;DR: In this paper, surface texture formation is caused by an excess driving force which results in growth of grains with a low-surface-energy plane exposed at the substrate surface, since the surface energy of a crystallographic plane is a function of atmosphere and impurities adsorbed on the surface.
Abstract: Crystallographic texture formed at the surface during the sintering of 3 tape-cast Al2O3 substrates was studied as a function of sintering temperature and atmosphere The sintering atmosphere strongly influenced the surface texture formed A strong (001) basal-plane fiber texture normal to the plane of the substrate is produced when commercial green substrates are sintered in air at 1600° to 1700°C; sintering in vacuum (< 2 × 10-6 mm Hg) or dry H2 produces a weaker texture Grain growth is a necessary but insufficient condition for the formation of a strong surface texture It is proposed that surface texture formation is caused by an excess driving force which results in growth of grains with a low-surface-energy plane exposed at the substrate surface Since the surface energy of a crystallographic plane is a function of atmosphere and impurities adsorbed on the surface, both these factors should have a pronounced effect on surface texture formation, as observed in the present study
TL;DR: In this article, the effect of V2O5 additive on the sintering of SnO2 was studied by measuring relative density and isothermal shrinkage in the temperature range 800 to 1400°C.
Abstract: The effect of V2O5 additive on the sintering of SnO2 was studied by measuring relative density and isothermal shrinkage in the temperature range 800 to 1400°C. The optimum amount of V2O5 added was 10wt%, which might be the solid solubility limit of vanadium ion into SnO2 lattice. With this amount of V2O5, the shrinkage behavior agreed with a model based on liquid-phase sintering at lower temperature. At higher temperature above 1250°C, the major parts of the densification occurred very rapidly and was followed by a much slower sintering process typical of volume diffussion. The fast early shrinkage might be caused by the capillary forces of liquid and the rapid formation of solid solution.Grain growth followed the expression G3-G03=At with an apparent activation energy of 104kcal/mol. The volume diffusion of oxygen ion was rate determining step for grain growth in this experiment.
TL;DR: In this article, high-rate physical vapor depostion techniques (HRPVD) were used to prepare fine-grained materials having superior resistance to swelling induced by fast-neutron irradiation.
Abstract: Molybdenum, niobium, and vanadium bulk deposits produced by high‐rate physical vapor depostion techniques (HRPVD) were analyzed for impurity content, grain size and morphology, yield strength, hardness, and bend ductility. Yield strengths of Mo and Nb were comparable to those of wrought material having equivalent grain sizes, while the yield strength of vapor‐deposited V was superior to that of wrought V because of its ultrafine (0.7 μm) grain size. Ultrafine‐grained refractory metals, such as the V deposits produced in this study, may greatly reduce void formation and growth, which causes dimensional changes and degradation of mechanical properties in reactor structural components. It is suggested that HRPVD techniques may be used to prepare fine‐grained materials having superior resistance to swelling induced by fast‐neutron irradiation.