Grain Growth Rate Research Articles

Computer Model of Recrystallization Texture in Aluminum Alloys

During recrystallization, frequency of occurrence of nuclei with certain orientation depends on the location of the nucleation site, the energy stored at that location and the rate of release of stored energy. A computer model of nucleation of recrystallization process in cold rolled aluminum is developed based on the analysis of misorientation distributions around the nuclei of different orientations and the measured orientation dependent elastic energy stored in the specimen. Comparison of selected locations of nucleation sites with experiment shows that Cube nuclei are located much more randomly in the cold rolled matrix than the rolling texture components, namely, copper, brass, and sulfur. A specific range of rate of release of stored energy increases the frequency of occurrence of the Cube nuclei. Information on the stored energy after cold deformation and stress relieving provides a great deal of understanding on the mechanism that controls the primary recrystallization in deformed metals. From the diffraction peaks that are measured using X-rays in 88% cold-rolled and stress-relieved can body aluminum alloy, stored energy as a function of crystal orientation is calculated. The rate of reduction of stored energy plays a major role in deciding the rate of nucleation of new grains with different orientations. The stored energy of deformation and unique misorientation distribution that cube grains have in the cold rolled matrix is responsible for the enhanced growth rate of the nucleated cube grains. The simulated results are compared with the experimental data. Agreement of these results suggests that in the development of the cube texture, both oriented nucleation and oriented growth play an important role. Software was developed to simulate texture and microstructure transformation during the annealing process.

Improvement in the Temperature Stability of a BaTiO3‐Based Multilayer Ceramic Capacitor by Constrained Sintering

In this study, a self‐constrained BaTiO3 material system, composed of a low‐fire BaTiO3‐based X7R (ΔC/C±15% within −55° to 125°C) MLCC dielectric and a high‐fire, BaTiO3‐based X7R MLCC dielectrics eliminated sintering aid that are laminated on both sides of the BaTiO3‐based X7R MLCC, has been developed. The temperature dependence of capacitance of the BaTiO3‐based X7R MLCC is significantly improved to satisfy X8R requirements over the entire temperature range studied (ΔC/C±15% within –55° to 150°C) using the self‐constrained sintering. The curie temperature of BaTiO3‐based X7R MLCC increases on increasing the thickness of the constraining layers. Compared with the specimen fired by free sintering, a substantial reduction in grain size, leading to a decrease in dielectric constant, was observed in the specimen fired by constrained sintering with the thickness of the constraining layer being 170 μm. The increase in Curie temperature and decrease in grain size of the specimen fired by constrained sintering can be explained in terms of the presence of in‐plane tensile stress. The in‐plane tensile stress that introduces a friction force between the multilayer matrix and the nonshrinkage constraining layers to suppress the in‐plane shrinkage and to inhibit the rate of grain growth was formed during constrained sintering.

Microfabrics in carbonate mylonites along a large-scale shear zone (Helvetic Alps)

Carbonate mylonites with varying proportions of second-phase minerals were collected at positions of increasing metamorphic grade along the basal thrust of the Morcles nappe (Helvetic nappes, Switzerland). Variations of temperature, stress, and strain rate, changes in chemistry of solid and fluid phases, and differing degrees of strain localization and annealing were tracked by measuring the shapes, mean sizes, and size distributions of both matrix and second-phase grains, as well as crystal preferred orientation (CPO) of the matrix. Field structures suggest that strain rate was constant along the fault. The mean and distribution of the calcite grain sizes were affected most profoundly by temperature: Increased temperature, presumably accompanied by decreased stress, correlated with larger mean sizes and wider size distributions. At a given location, the matrix grains in mylonites with more second-phase particles are, on average, smaller, have narrower size distributions, and have more elongate shapes. For example, mylonites with 50 vol.% of second phases have matrix grain sizes half that of pure mylonites. Changes in calcite chemistry and the presence of synkinematic fluids seemed to influence microfabric only weakly. Temporal variations in conditions, such as exhumation-induced cooling, apparently provoke changes in temperature, stress, and strain rate along the nappe. These changes result in further strain localization during retrograde conditions and cause the grain size to be reduced by an additional 50%. The matrix CPO strengthens with increasing temperature or strain, but weakens and rotates with increasing second-phase content. These fabric changes suggest differing rates of grain growth, grain size reduction, and development of CPO owing to variations in the deformation conditions and, perhaps, mechanisms. To interpret natural mylonite structures or to extrapolate mechanical data to natural situations requires careful characterization of the microfabric, and, in particular, second-phase minerals.

Study of Grain Growth Kinetics in Submicrocrystalline Armco-Iron

The paper is devoted to the problem of thermal stability of ultra-fine grained (submicrocrystalline) materials prepared by severe plastic deformation. A basis of the paper lies in a fact that there is practically no grain growth in submicrocrystalline materials when annealing temperature is less than 0.35Tm. Reasons of high thermal stability of submicrocrystalline materials at low temperatures are widely discussed in literature. One of them is the affect of triple junction drag on grain boundaries motion. During annealing at a low temperature triple junction drag controls microstructure evolution in submicrocrystalline materials, and this phenomenon can be used to improve their thermal stability at high temperatures. The aim of this paper is to investigate grain growth kinetics in a two-step regime, low temperature and high temperature annealing. The experiments on grain growth were performed in submicrocrystalline Armco-iron fabricated by high pressure torsion. It is established that long-time low temperature pre-annealing reduces the grain growth rate in following high temperature annealing by a factor greater than two.

Mechanism of Germanium-Induced Perimeter Crystallization of Amorphous Silicon

We report a study aimed at highlighting the mechanism of a new amorphous silicon crystallization phenomenon that originates from the perimeter of a germanium layer during low-temperature annealing . Results are reported on doped and undoped amorphous silicon films, with thicknesses in the range , annealed at a temperature of 500 or . A comparison is made of crystallization arising from Ge and SiGe layers and the role of damage from a high-dose fluorine implant is investigated. Plan-view scanning electron microscope images show that perimeter crystallization is only present in amorphous silicon films with thicknesses , and that the crystallization width increases with decreasing film thickness and increasing doping level. Cross-sectional scanning electron microscope images show that the perimeter crystallization originates from grains at the bottom of the amorphous silicon film. The perimeter crystallization phenomenon disappears when the amorphous silicon is implanted with fluorine and when an layer is employed instead of germanium. The perimeter crystallization is due to the formation of large grains as a result of an increased growth rate of pre-existing grains and this is attributed to the strain generated by the thermal expansion of the germanium layer during anneal.

Activities of Enzymes for Sucrose-Starch Conversion in Developing Endosperm of Rice and Their Association with Grain Filling in Extra-Heavy Panicle Types

Rice cultivars with numerous spikelets per panicle (extra-heavy panicle types) frequently fail to exhibit their high yield potential due to low grain filling. Existing genetic variation in grain filling, however, opens possibilities for genetic improvement for this trait. We studied the correlation between grain filling and the activities of enzymes for sucrose-starch conversion in developing endosperm. The activity of sucrose synthase (EC 2.4.1.13, SuSy) and ADPglucose pyrophosphorylase (EC 2.7.7.27, AGPase), were measured in three extra-heavy panicle types and a standard cultivar grown at two locations under different environmental conditions. The proportions of grains with definite specific gravities and the rate of grain filling were adopted as the parameters related to grain filling. AGPase activity, but not that of SuSy, was consistently correlated to high proportions of high-density grains (specific gravity > 1.20) and high rates of grain growth in spikelets, particularly in those on secondary branches in which low grain filling is the rule. Such correlation was also detected in spikelets on primary branches which generally show better grain filling, but only early stages. Therefore, a high activity of AGPase might contribute to the reduction of the sucrose concentration by accelerating sucrose metabolism at the developing seed, a sink terminus of the phloem. Thus the sink-directed phloem transport of sucrose would be promoted, resulting in improved grain filling of extra-heavy panicle types. SuSy would play some roles in such a cultivar difference in grain filling, but depending on environments.

Effect of photon irradiation on the process of recrystallization of thin metallic films

Recrystallization of thin polycrystalline films of Au, Pt, and Pd obtained by thermal evaporation and condensation in a vacuum on silicon plates that are not warmed up and are coated on both sides with silicon oxide has been studied by transmission electron microscopy. It has been established that the rate of normal grain growth in such films is higher upon photon treatment by the radiation of power xenon lamps (spectral region of 0.2–1.2 μm) than upon heat treatment. A quantitative estimate of the effect revealed indicates a change in the mechanism of the process that controls migration of grain boundaries. The effect is connected with the possible activation of hypersonic waves owing to the coexistence of phonon and electron excitations localized in nanosized regions of metallic films.

In situ transmission electron microscopy of ion irradiated Fe–Pt alloy thin films

We report the microstructural evolution during irradiation of FePt and FePt 25at.% thin films sputter deposited onto electron transparent silicon monoxide substrates. The films were studied in situ for 500keV Kr+ irradiation up to a fluence of 1015ions∕cm2 or 4displacements∕atom (dpa). Upon irradiation to approximately 1dpa, the initial disconnected granular morphology became continuous. In particular, for FePt, accelerated grain growth was observed once the continuous morphology was achieved during ambient temperature irradiation. No atomistic (chemical) ordering from the as-deposited A1 phase into either the L10 FePt or L12 Fe3Pt phases was observed during ambient temperature irradiation. After irradiation, the specimens were then in situ annealed. The intermetallic ordering temperature, compared to that of an unirradiated film, was lowered by ≈200°C for FePt 25at.%. No decrease in the ordering temperature was observed for irradiated FePt. The rate of FePt grain growth during annealing was very similar for both irradiated and unirradiated films over the 25–650°C temperature range investigated.

Plasticity of sorghum kernel weight to increased assimilate availability

Understanding source or sink limitations on crop yield is critical for the rational design of agricultural practices as well as breeding strategies. In the present article, we studied sorghum [ Sorghum bicolor (L.) Moench] source–sink yield limitations during grain filling, and tested the hypothesis that the time in which kernel maximum water content is reached during grain filling defines a temporal limit for the crop to profit from source increases. Earlier studies have never tested increasing assimilate availability per kernel in different developmental stages. We conducted a field experiment increasing assimilate availability per kernel at anthesis and 15 days after anthesis in commercial hybrids. The anthesis treatment was aimed to increase assimilates per kernel from early grain filling, and the 15 days after anthesis treatment from the stage kernel maximum water content was achieved. Both treatments removed 50% of the kernels from one side of the panicle. Kernel dry weight (KW), kernel water content and kernel volume were measured in apical and basal positions of the panicle throughout grain filling. Increased assimilate availability always yielded a higher KW (∼34% increase). This KW increase was consistent across the two kernel developmental stages when the treatment was imposed, the panicle position and hybrid. Achieving maximum water content did not prevent kernels from increasing their weight when assimilates were subsequently increased. Final KW was closely related to maximum kernel volume ( r 2 = 0.72; n = 42; p < 0.0001). Increased assimilate availability per kernel promoted changes in both kernel growth rate and duration of grain filling. We applied a quantitative approach for determining the magnitude of sorghum KW changes in response to assimilate availability changes during grain filling. This allowed us to compare our data to previously published articles, and to determine any general response pattern across environments. The analysis supported our observation that sorghum KW is highly responsive to increased assimilates, and indicated that increased assimilate availability during filling always increased sorghum KW. As such, growth of sorghum kernels is predominately source limited; breeding and management practices aimed to increase assimilate availability per kernel will be likely to enhance sorghum yield. Results show that the crop has the capacity to profit from source increases even after the initial grain-filling stages have occurred.

Thermodynamic evidence for a poisoning mechanism in the Al–Si–Ti system

The poisoning of grain refinement in aluminium alloys owing to the presence of silicon is investigated using CALPHAD based thermodynamic modelling software. The existence of primary phases other than α-aluminium, namely TiSi2 and TiSi, which are stable at typical melt holding temperatures, is consistent with microstructural observations of other researchers. The compositional and temperature range of these phases are calculated. The software is also used to determine the effect of silicon and titanium additions on the growth rates of α-aluminium grains via the growth restriction parameter Q. These results are used to explain poisoning in silicon containing foundry alloys via a thorough review and discussion of the relevant literature.

Grain weight responses to post-anthesis spikelet-trimming in an old and a modern wheat under Mediterranean conditions

Average grain weight is a major yield component contributing to its variation, especially in Mediterranean regions where grain weight is frequently exposed to terminal stresses affecting grain growth. Most of the literature agrees that wheat grain growth is hardly limited by the source. However, no source–sink ratios studies seem to have been conducted in the Mediterranean region to determine to what degree wheat grain growth is actually limited by the source in these particular regions. We conducted two field experiments in Catalonia (north-eastern Spain), where an old cultivar (Anza) and a more recently released one (Soissons) were sown in a range of different nitrogen and water availabilities and sowing dates. This was to analyse the degree of source limitation for grain growth. Sink size was modified by removing half of the spikelets c. 10 days after anthesis, virtually doubling the availability of assimilates per grain effectively growing. Trimming the spikes did not produce significant changes in grain growth rate or duration of grain filling. Consequently, grain weight did not respond noticeably to the reduction in sink demand and any eventual response has been far from representing a strong competition among grains during grain filling.

The effect of drawing velocity and phase transformation on the structure of directionally annealed iron

Undeformed iron bars were directionally annealed under various processing parameters. Columnar grains having an aspect ratio as high as 50 were produced at optimum processing conditions of a hot zone temperature of 850 °C, a 200 °C/cm temperature gradient and a drawing velocity of 1 μm/s. Equiaxed grains were formed both when the drawing velocity was low, and when it exceed the maximum growth rate of grains. The ferrite to austenite phase transformation hindered the columnar grain growth. A novel microstructure with columnar grains in the outer region, whose longitudinal axis parallels to the drawing direction, and fine equiaxed grains at the center of the specimen was observed. The skin effect of high frequency induction heating during the directional annealing was used to explain the formation of this novel microstructure.

Investigation of low temperature thermal stability in bulk nanocrystalline Ni

Grain growth behavior of bulk nanocrystalline Ni, prepared by an electrodeposition technique with average grain sizes of 20 and 15 nm was investigated in the homologous temperature ( T/ T m) range of 0.20–0.40. In studying grain growth, the techniques of X-ray diffraction and transmission electron microscopy were used. The results show that in the temperature range of 0.20–0.30 T m, there is no appreciable grain growth, even after long annealing times. However, in the temperature range of 0.3–0.4 T m, the rate of grain growth was rapid during the initial period of annealing, which decreases with increase in time. The value of time exponent, n, deduced from the grain growth equation of the general form D 1 / n − D 0 1 / n = K t was found to be approximately 0.1 for both grain sizes of Ni. At temperatures higher than 0.3 T m, an approximate activation energy of 105 ± 3 kJ/mol, which is close to the activation energy for grain boundary diffusion in polycrystalline Ni, was measured. At temperatures lower than 0.3 T m, an approximate activation energy of 11 ± 3 kJ/mol was found. It is suggested that this low activation energy represents the energy for the re-ordering of the nanocrystalline grain boundaries.

Modeling polycrystals with regular polyhedra

Polycrystalline structure is of paramount importance to materials science and engineering. It provides an important example of a space-filling irregular network structure that also occurs in foams as well as in certain biological tissues. Therefore, seeking an accurate description of the characteristics of polycrystals is of fundamental importance. Recently, one of the authors (MEG) published a paper in which a method was devised of representation of irregular networks by regular polyhedra with curved faces. In Glicksman's method a whole class of irregular polyhedra with a given number of faces, N, is represented by a single symmetrical polyhedron with N curved faces. This paper briefly describes the topological and metric properties of these special polyhedra. They are then applied to two important problems of irregular networks: the dimensionless energy 'cost' of irregular networks, and the derivation of a 3D analogue of the von Neumann-Mullins equation for the growth rate of grains in a polycrystal.

Misorientations of garnet aggregate within a vein: an example from the Sanbagawa metamorphic belt, Japan

AbstractIn this study, the chemistry and microstructure of garnet aggregates within a metamorphic vein are investigated. Garnet‐bearing veins in the Sanbagawa metamorphic belt, Japan, occur subparallel to the foliation of a host mafic schist, but some cut the foliation at low angle. Backscattered electron image and compositional mapping using EPMA and crystallographic orientation maps from electron‐backscattered diffraction (EBSD) reveal that numerous small garnet (10–100 μm diameter) coalesce to form large porphyroblasts within the vein. Individual small garnet commonly exhibits xenomorphic shape at garnet/garnet grain boundaries, whereas it is idiomorphic at garnet/quartz boundaries. EBSD microstructural analysis of the garnet porphyroblasts reveals that misorientation angles of neighbour‐pair garnet grains within the vein have a random distribution. This contrasts with previous studies that found coalescence of garnet in mica schist leads to an increased frequency of low angle misorientation boundaries by misorientation‐driven rotation. As garnet nucleated with random orientation, the difference in misorientation between the two studies is due to the difference in the extent of grain rotation. A simple kinetic model that assumes grain rotation of garnet is rate‐limited by grain boundary diffusion creep of matrix quartz, shows that (i) the substantial rotation of a fine garnet grain could occur for the conditions of the Sanbagawa metamorphism, but (ii) the rotation rate drastically decreased as garnet grains formed large clusters during growth. Therefore, the random misorientation distribution of garnet porphyroblasts in the Sanbagawa vein is interpreted as follows: (i) garnet within the vein grew so fast that substantial grain rotation did not occur through porphyroblast formation, and thus (ii) random orientations at the nucleation stage were preserved. The extent of misorientation‐driven rotation indicated by deviation from random orientation distribution may be useful to constrain the growth rate of constituent grains of porphyroblast that formed by multiple nucleation and coalescence.

Abnormal Grain Growth in Barium Titanate Doped with Alumina

The effect of additions of ≤1 mol% Al2O3 on abnormal grain growth in BaTiO3 sintered for periods of ≤60 min at 1350°C has been studied. Addition of ≤0.2 mol% Al2O3 caused an increase in the nucleation and growth rates of abnormal grains, with further additions causing a decrease. This behavior is explained by interface‐controlled growth. Dopant adsorption reduces both the edge free energy and the step velocity of a grain, causing the nucleation and growth rates of abnormal grains to increase, pass through a maximum, and then decrease with increasing dopant concentration.

Electromigration study in the eutectic SnBi solder joint on the Ni/Au metallization

Microstructural evolution and interfacial reaction in the eutectic SnBi solder joint on the Ni/Au metallization with and without the current stressing of 6.5 × 103 A/cm2 at 70 °C for 5 to 15 days were investigated. Electromigration is found to have significant effects not only on the phase formation at the joint interface but also on the phase coarsening and mass accumulation of Bi in the solder. In the solder joint without the current stressing, only a thin Ni3Sn4 phase was formed at the joint interface. For the solder joint with the current stressing, in addition to the Ni3Sn4 phase, a thick Au–Ni–Bi–Sn phase was formed at the joint interface after 10 days. However, the Au–Ni–Bi–Sn phase was not observed at the anode-side joint interface after 15 days of current stressing. Coarsening of the Bi-rich grain in the solder joint with the current stressing was much faster than that without the current stressing. Mass accumulation of Bi was observed at the anode side of the solder joint with the current stressing and the thickness of the Bi-rich accumulation layer increased with current stressing time. Based on the accumulation rate of the Bi-rich layer and the growth rate of the Bi-rich grain, the product of diffusivity and effective charge number of Bi in the eutectic SnBi solder is calculated to be 4.72 × 10−10 cm2/s.

Grain growth in Zr–Fe thin films during in situ ion irradiation in a TEM

In situ ion-beam irradiation was used to study irradiation induced grain growth in co-sputter-deposited Zr/xFe (0%⩽x⩽4.5%) nanocrystalline thin films. Samples were irradiated with 500keV Kr ions to fluences in excess of 1016ions/cm2 (on the order of 80–100dpa), at irradiation temperatures ranging from 20K to 573K. The average grain size increased monotonically with ion fluence until it reached a saturation value which depends both on temperature and on the presence of Fe. Similarly to thermal grain growth, the ion irradiation induced grain growth curves could be best fitted with curves of the type: Ln-L0n=KΦ. Grain growth at 20K is similar to that which occurs at 298K. Above 298K, the rate of grain growth increases with irradiation temperature.

Fabrication of Textured Bismuth Sodium Titanate Using Excess Bismuth Oxide

Bi0.5Na0.5TiO3 (BNT) bulk ceramics with a preferred <100> orientation (texture) were prepared by the reactive-templated grain growth method using platelike Bi4Ti3O12 (BiT) particles as templates for BNT. The texture did not develop extensively in stoichiometric BNT, but the addition of excess Bi2O3 to BNT enhanced the texture development. The role of excess Bi2O3 was examined. The calcined compacts were composed of matrix grains with random orientation and <100>-oriented grains transformed from aligned BiT particles, and texture developed by the preferential growth of oriented grains at the expense of matrix grains. In stoichiometric BNT, the growth rate of matrix grains was high and the conditions for the preferential growth of the oriented grains were disrupted. Excess Bi2O3 reduced grain growth rate, and the conditions for preferential growth were maintained, resulting in the development of highly textured BNT. The resultant textured BNT ceramic exhibited 70% higher piezoelectric d31 and electromechanical kp coefficients than nontextured BNT.

The influence of triple junction kinetics on the evolution of polycrystalline materials during normal grain growth: New evidence from in-situ experiments using columnar Al foil

Abstract During grain growth in 2D systems triple junction kinetics may significantly influence not only the rate of grain growth but also the geometric evolution of the grain boundary network. In this contribution we analyse results from in-situ heating experiments coupled with electron backscatter diffraction analysis using a columnar Al foil. It is shown that (a) the von Neumann–Mullins relation is not always satisfied, (b) there is a marked discontinuity and heterogeneity in TJ motion in space and time and (c) grain boundaries evolve from predominately curved to straight boundaries. To interpret these results we introduce 3 main types of triple junctions Tc, Tp, and Ts, which are made up by at least 2 concave, 2 convex, and 3 straight boundaries, respectively. Analyses show that triple junction drag plays a significant role during grain growth. Data suggest that the drag effect of Tp is higher than that of Tc. In addition, triple junctions with 3 low-angle boundaries are exceptionally stable, while th...