Giant Grains Research Articles

Formation of Giant Columnar Grains in High-Purity Iron by Hot-Rolling

The microstructure change of three kinds of high-purity irons (HP, MP and LP irons) by hot-rolling at various temperatures was investigated. Columnar grains in high-purity irons develop along the normal direction after hot-rolling in the γ-phase region. The growth of columnar grains depends on the purity of the iron: the width and height of columnar grains increase with the increase of the purity of the iron. Giant columnar grains of HP-iron grow to the center of the thickness. Columnar grains do not develop by hot-rolling in the α-phase region nor by heating in γ-phase region without hot-rolling. Apparently, the γ → a transformation after hot-rolling in the γ-phase region plays an important role in the growth of giant columnar grains. The crystal orientation of giant columnar grains was determined by an electron back scattering pattem method. The transformed α-texture was calculated from the y-texture with {112} by using the Krudjumov-Sachs relationship. The calculated α-texture is in good agreement with the measured crystal orientations except for {100} . Furthermore, the formation mechanism of giant columnar grains has been proposed.

Influence of Purity and Forging Temperature on the Microstructure of High-Purity Iron

The influence of purity and forging temperature on the microstructure of high-purity iron has been investigated by using two kinds of high-purity iron; Iron-K of 99.981 mass% purity and Iron-A of 99.993 mass% purity. Both of high-purity irons could be forged to more than 80% reduction in height at room temperature without cracking. The hardness and the microstructure of as-forged irons are not uniform. Therefore, the behavior of recovery and recrystallization of forged irons are not uniform through the specimens. The microstructure of forged iron is strongly affected by the purity and the forging temperature. It is emphasized that giant columnar grains grow in parallel to the forging direction in Iron-A forged at 1263 K, above the α-γ transformation temperature. However, uni-axual grains with random orientation grow though Iron-K forging at 1263 K. These recrystallization behavior relates to the large mobilities of α/γ interface and grain boundaries due to the effect of purification, although the formation mechanism is not obvious.

The formation of (0 0 1) oriented Ag 2Se films on amorphous and polycrystalline substrates via polymorphic-phase transition

Silver selenide thin films have been prepared on amorphous and polycrystalline substrates by the solid–vapour-phase reaction of vacuum deposited polycrystalline silver films and selenium. We have found earlier that at given conditions (0 0 1) oriented giant (100–300 μm) grained Ag 2Se layers develop. The details of formation of these peculiar films have been now studied by ex situ and in situ transmission electron microscopy. By quenching the samples from the reaction temperatures to room temperature earlier unknown intermediate stages of the formation of oriented giant grains were revealed. We observed, that during the reaction of polycrystalline Ag and selenium polycrystalline Ag 2Se film develops, which can then transform to a (0 0 1) oriented giant grained one. The formation of these oriented films occurred always only on slowly cooling during the polymorphic transition from the high-temperature cubic — to the low-temperature orthorhombic phase as a result of the selective appearance and fast growth of (0 0 1) nuclei of the orthorhombic Ag 2Se at the free upper film surface. The enthalpy difference between the HT and LT phases and the low surface energy of the (0 0 1)Ag 2Se is supposed to be the driving force of this process. The fundamental role of the polymorphic-phase transition in the formation of (0 0 1) oriented, giant grained Ag 2Se films will for the first time be shown in the present paper.

Growth of giant grains in silver thin films

Growth of giant grains in silver thin films

Influence of the Addition of Bi2O3 on the Grain Growth and Magnetic Permeability of MnZn Ferrites

Additions of Bi2O3 were used to promote grain growth and to increase magnetic permeability during sintering of MnZn ferrites. The results showed that small additions of Bi2O3 of <0.05 wt% remarkably increase the permeability of MnZn ferrites. On the other hand, addition of 0.05 wt% Bi2O3 induced the formation of a microstructure composed of giant grains with trapped pores embedded in a normal microstructure. The permeability of these samples showed a pronounced secondary maximum in permeability. At still higher Bi2O3 concentrations, above 0.2 wt%, the grain growth was retarded and a normal microstructure appeared; however, the magnetic permeability was strongly reduced.

Development of needle-shaped grains from Bi2Sr2CaCu2O8+x with high critical current density suitable for making superconducting wires

Abstract We present a grain microstructure for Bi(2212) consisting of only giant needle-shaped grains of around 1.5 mm length and 100 μ m diameter. We study the structural and chemical changes suffered by a conventional ceramic Bi(2212) sample in the course of the thermal treatment used to obtain those giant needle-shaped grains. For that, different samples of the same batch were treated with incomplete thermal treatments, and the resulting samples were analysed by using scanning electron microscopy (SEM), optical microscopy, energy dispersed spectroscopy (EDS), inductively coupled plasma (ICP) and X-ray diffraction (XRD). To verify the superconducting nature of the needle-shaped grains, we have performed magnetization, resistivity, and critical current measurements on the original ceramic sample, and on that formed as giant needle-like grains. The critical temperature of these last grains is nearly the same as that of the ceramic sample ( T c ∼90 K), which is a high value for the Bi(2212) compound. The critical current density ( J c ) of the needle-shaped grains is around 2500 A/cm 2 at 77 K and in absence of applied magnetic field, a value comparable with that presented for the best wires and thick films. Not only are the shape and the size of these grains very suitable for making superconducting wires, but also the superconducting properties, T c and J c , are both high enough to be confident about the possibility of improving the actual Bi(2212) superconducting wires for high current applications.

Formation of giant-grain copper interconnects by a low-energy ion bombardment process for high-speed ULSIs

When Cu films are grown on SiO 2 by a low-energy ion bombardment process under a sufficient energy deposition, the film exhibits almost perfect crystal orientation conversion from Cu(111) to Cu(200) upon post-metallization thermal annealing, which is accompanied by the growth of giant grains as large as several hundred micrometers. The room-temperature resistivity of such giant-grain Cu films is 1.76 μΩ cm, which is almost the same as the bulk value (1.72 μΩ cm). The giant-grain Cu interconnects exhibit an electromigration resistance three orders of magnitude larger than Al-alloy interconnects, when the life-test data are extrapolated to room temperature. We have shown that the employment of a non-oxidizing ambient, such as N 2 ambient, is essential for electromigration life-test of Cu interconnects, because Cu is easily oxidized in air. We have investigated the properties of Ta thin films as a diffusion barrier between Cu films and Si substrates using p-n junction diodes. It is shown that a 10 nm thick Ta film works as a effective barrier for temperatures up to 500 °C.

Second meiotic division restitution (SDR) 2n pollen formation in diploid and hexaploid species of Asparagus

Plants of two cultivars of 2x A. officinalis L. and two related ornamental species, 2x A. plumosus Baker and 6x A. densiflorus (Kunth) Jessop cv. Sprengeri were screened for production of pollen of heterogeneous size. Twenty four plants out of thirty-one studied produced this type of pollen, with frequencies of 3% or more large pollen. Some of these plants also produced giant grains. The numerically unreduced pollen arose by the lack of chromosome migration at Anaphase II in either one or both cells of a meiocyte, followed by the absence of cytokinesis in cells with abnormal chromosome behavior, a Second Meiotic Division Restitution (SDR) cytological mechanism. Double unreduced pollen resulted from a similar mechanism acting at both Anaphase I and Anaphase II stages. The high frequency of plants which produced 2n pollen in significant amounts is taken as an indication that the modified meiosis observed is under genetic control.

Electrical Properties of Giant‐Grain Copper Thin Films Formed by a Low Kinetic Energy Particle Process

Formation of giant‐grain copper thin films on by a low‐kinetic energy particle process followed by thermal annealing has been investigated. When Cu films are grown on by the process under a sufficient amount of energy deposition, they exhibit almost perfect crystal orientation conversion from Cu(111) to Cu(100) upon thermal annealing. Such crystal orientation conversion is accompanied by the giant grain growth in the film as large as 100 μm. With regard to these phenomena, the effects of the ion flux density and of the ion bombardment energy have been studied. It was found that the crystal orientation conversion and the accompanying grain growth are governed by the total energy deposited to the as deposited film. The Cu film resistivity decreases when the giant grain growth occurs in the film due to the increase in the grain boundary scattering. At room temperature, the resistivity of the Cu film having giant grains is 1.76 μΩ · cm, almost equal to the bulk resistivity of 1.72 μΩ · cm. When the temperature is reduced to a low temperature of 12 K, the resistivity becomes as low as 18.3 nΩ · cm, which is almost one order of magnitude lower than that of the as deposited film also measured at 12 K (152 nΩ · cm). Furthermore, it is confirmed that the interconnects formed by giant‐grain Cu films can with‐stand from one to two orders of magnitude larger currents than Al‐Si‐Cu alloy interconnects, provided both interconnects exhibit the same electromigration lifetime. It is also shown that giant‐grain Cu interconnects exhibit longer lifetime than the Al‐Si‐Cu alloy interconnects by three to four orders of magnitude under the same current stress. These experimental results demonstrate that the giant‐grain Cu film is a very promising material to form low‐resistivity, high‐reliability interconnects for future subhalf micron ultralarge scale integrated circuits.

Anomalous grain growth and texture formation in alloyed electrical sheets

The early stage of anomalous grain growth of iron-silicon sheets is characterized by coalescence of similarly oriented grains with dislocation emission rather than grain boundary migration. Regions of similarly oriented grains may originate from giant grains forming during the first hot rolling pass and involving orientation differences up to about 30°.

Influence of free forging conditions on austenitic grain growth in constructional steel

1. The initial period of austenitic grain growth in heating of a hot forged billet of 50G-SSh steel and of forgings after free forging is characterized by the formation of a mixed grain structure of No. 8 fine grains and No. 3-0 coarse. 2. Reforging of the billets of 50G-SSh steel with e=90% reduced the temperature of the start of austenitic grain growth from 1000 to 950°C. 3. The formation of a mixed grain structure in the initial period of growth is characterized by nonuniform distribution of the coarse grains in the cross section of the forging. At low temperatures of heating for forging (900°C) the giant grains are uniformly distributed in the volume of the steel, while with an increase in the temperature of heating for forging the coarse grains are concentrated in the center of the forging in the regions of the “forging cross”. 4. The higher the temperature of heating for forging and the temperature of the finish of forging, the coarse the giant grains formed in the initial period of grain growth.

Factors Affecting Grain Enlargement in Wheat

When most of the grains were removed from wheat ears the remaining grains developed increased numbers of aleurone and endosperm cells, and the increased grain volume was accompanied by an enlarged endosperm cavity. The giant grains usually synthesized starch more rapidly than normal grains. Flag leaf photosynthesis was unaffected and additional sugar was retained in the culm and glumes. Total nitrogen and free amino acid content increased. Gibberellin and auxin concentrations were greater in the glumes of the partly degrained ears, and auxin in the grains was also greater than in equivalent grains from intact ears.

Giant grains?

Giant grains?

Giant Grains in Orion

Giant Grains in Orion

Pollen-white cell interactions

One of the early interactions in vitro of white cells (except lymphocytes) with low ragweed pollen grains is the adherence of white cells to pollen grains. This is augmented by sera from either normal and sensitized guinea pigs or normal and atopic human subjects. Two morphologically distinct shapes of adhering white cells are evident. These consist of round and crescent-shaped white cells. Most white cells which adhere to low and giant ragweed pollen grains are round. In contrast, most white cells which adhere, in the presence of serum, to pollen grains of other species or to defatted low ragweed pollen grains are crescent shaped. Adherence is optimal under physiologic conditions, requires viable white cells, and is inhibited by glycolytic poisons. The factor or factors in the serum (pollen adherence factor[s]: PAF) which augment the adherence of white cells to pollen grains are significantly increased in sera of guinea pigs which have been previously injected with low ragweed pollen grains in Freund's complete adjuvant. PAF have been selectively removed by absorption with whole ragweed pollen grains. Antibodies to sheep red cells, skin-sensitizing antibodies, dialysis of serum, and low ragweed extracts do not significantly affect PAF activity. Heat inactivation of serum diminishes but does not stop PAF activity. The initial interactions of white cells with pollen grains in vivo, upon intraperitoneal injection of pollen, are similar to those which occur in vitro.

Studies on the male gametophyte in angiosperms, VI. Abnormalities in the pollen development of some <i>Crinum</i>-species

1. Abnormalities in pollen development under natural conditions were statistically investigated in five species of Crinum, C. asiaticum var. japonicum, C. latifolium, C. gigas, C. Moorei and C. sp. (Powelli?, pink-flowered), because of the necessities, 1, for the analysis of the experimental disturbances and climatic influences upon the pollen development, 2, for the cytological analysis of the hybridity.2. In the genetically homologous species, dwarf, giant and sometimes twin pollen grains are formed in very low percentages (see the first table).3. Examination of pollen tetrad formation showed that most of the dwarf grains were derived from both pentads and hexads, and the giant were from monads.The mode of polyad formation in several cases suggests that those abnormalities of low frequencies in the genetically homologous individuals may be ascribed to an accidental failure of balance among the physical and chemical conditions in a few pollen mother cells, which has been caused by interactions of those conditions in the course of meiosis, rather than to the presence of slightly heterotypic nature in chromosomes of those individuals.4. In C. asiaticum var. japonicum and C. latifolium, the abnormal grains appeared in a close proximity of their frequencies in one case, as seen in the following table:This fact seems to support the hypothesis advanced above (3).5. In the species which is expected to be of hybrid origin, abnormal pollen grains appear in very high frequencies, and viable and normal grains in very low (see the following table):In addition to it, there are certain extreme abnormalities among them which could not be found in the homologous individuals, such as ultra-giant pollen grains, giant twin grains, 3-nucleate and 4-nucleate grains. Though these abnormalities can not be expected as induced by only the failure of the pairing of the chromosomes in the first meiotic division, most of the abnormal dwarf grains may be apparently expected as induced by it. So, it may be said that the abnormalities in the pollen development in a hybrid species must be discussed from more than one point of view.

Further Studies on the Origin of Giant Pollen Grains in Petunia

1. The material used in the present study is Sutton's New Blue Bedding (2n=14) and Sutton's Leviathan (2n=28). Some branches with young buds were put in flasks filled with water and kept in ovens at 40°C, 42°C, 45°C and 47°C respectively. After differing lengths of time buds were examined in Belling's acetocarmine. Irregularities were observed in regard to both karyokinesis and cytokinesis; only the latter will be reported here. 2. At higher temperature tetrads formation proceeds in a manner different from the normal furrowing process (Fig.2-Fig.3). A narrow hyaline area appears at the middle of cells which gradually becomes clearer and bisects the cytoplasm (Fig.5). A wall is then formed around each daughter cell (Fig.6). The sister cells thus formed remain sticking to each other by the division plane and often fail to separate. The secondary division sometimes takes place in one or each of the daughter cells (Fig.8). As a result there are formed three or four daughter cells, all of which also remain sticking together very often, although a slight indication of separation is sometimes seen between the sister cells. Some pollen mother cells, on the other hand, are divided simultaneously into four parts which also remain stuck together (fig.9). Possibly the giant pollen grains are. derived from those cases in which sticking cells have fused together and have been enclosed within one and the same wall (Fig.10). 3. The fusion of cells can occur at later stages among microspores (Fig.11-Fig.17). When cells more than four in number or corresponding to more than four fuse together a super giant pollen grain larger than the tetraploid grain reported in my previous paper must naturally result (Fig.14). This fact also clearly accounts for the irregular shape of super giant pollen grains. 4. Fusion also takes place at earlier stages while the meiosis is still proceeding (Fig.19-Fig21). This must result in giant pollen grains or if any cytokinesis fails to occur, a super giant pollen grain. This sort of fusion is as rarely observed in the heated material as in the greenhouse material. Abnormal temperature (at least high temperature), therefore, may not be the important factor for its occurrence 5. A uninucleate interkinesis is found with at least fourty nine chromosomes (Fig.18). Cell dimension in this case is normal. This has probably been caused by cytomixis occurring at a certain stage of meiosis and has no relation with the formation of giant grains. 6. In the giant pollen grain formed by means of cell fusion the nuclei possibly do not fuse into one, so that in fertilisation only one haploid nucleus will join the egg nucleus. This, to some extents, accounts for the fact we reported at the previous meeting, namely that artificial pollination exclusively with giant pollen grains resulted only F1 progenies with a diploid number of chromosomes, although we have some reason to believe that the chromosome elimination must take place at a certain stage during the progress from pollen division to fertilisation, or much later.