Grain Growth

A model has been developed for evaluating grain size distributions in primary crystallizations where the grain growth is diffusion controlled. The body of the model is grounded in a recently presented mean-field integration of the nucleation and growth kinetic equations, modified conveniently in order to take into account a radius-dependent growth rate, as occurs in diffusion-controlled growth. The classical diffusion theory is considered, and a modification of this is proposed to take into account interference of the diffusion profiles between neighbor grains. The potentiality of the mean-field model to give detailed information on the grain size distribution and transformed volume fraction for transformations driven by nucleation and either interfaceor diffusion-controlled growth processes is demonstrated. The model is evaluated for the primary crystallization of an amorphous alloy, giving an excellent agreement with experimental data. Grain size distributions are computed, and their properties are discussed.

The work shows the effect of heat treatment T6 (solution and controlled precipitation of CuAl 2 ) on the microstructure of rheocast Al-4.5wt.% Cu alloy. Rheocast structures were obtained by partial melting to 40% liquid fraction from dendritic material with initial different grain sizes. Globular structures with grain sizes varying from 15 to 170 mm were produced and characterized for grain size, morphology, and Cu distribution and were mechanically tested, in both as-rheocast and T6 conditions. Results showed that increasing grain size results in a decrease in tensile and yield strengths, the latter according to a Hall -Petch type of relation. Elongation and constriction increase as grain diameter increases to a certain extent; for higher increase in grain diameter, these properties decrease. Concerning the effect of heat treatment in the structure, rheocast material requires more time for complete dissolution of the eutectic phase than cast structures, can keep higher Cu content in solution and prevents grain growth during holding. Greater improvement in mechanical properties is achieved by heat treatment in rheocast material.

A fuzzy logic inference system was designed to predict the grain size of Inconel 718 alloy after upset forging. The system takes as input the original grain size, temperature, and reduction rate at forging and predicts the final grain size at room temperature. It is assumed that the ...

NiO thin films grown on Si(1 0 0) substrate by electron beam evaporation and sintered at 500 and 700°C were irradiated with 120 MeV Au 9+ ions. The FCC structure of the sintered films was retained up to the highest fluence (3 Â 10 13 ions cm À2) of irradiation. In the low fluence (61 Â 10 13 ions cm À2) regime however, the evolution of the XRD pattern with fluence showed a wide variation, critically depending upon their initial microstructure. Though irradiation is known to induce disorder in the structure, we observe improvement in crystallization and texturing at intermediate fluences of irradiation.

Grain growth in systems of anisotropic grain boundary energy and mobility is investigated by computer simulations in a two-dimensional textured polycrystalline system. The energy and mobility are allowed to depend on both grain boundary inclination and misorientation. Mobility anisotropy alone does not significantly change the growth kinetics or statistical distributions of misorientation, grain size and number of grain edges, even though grain shapes evolve in a self-dissimilar fashion where the aspect ratio of grains and inclination distribution of grain boundaries are time dependent. Energy anisotropy, however, causes significant deviation of grain growth kinetics, misorientation and edgedistributions from the ones observed in isotropic systems. Moreover, misorientation distribution is skewed towards low energy (special) boundaries. Size distributions are similar in all cases. Mobility anisotropy influences grain growth kinetics only when energy is also anisotropic. Variation of misorientation distribution with time plays the key role in determining the grain growth behavior. 

Thin films of (Bi 0.5 Sb 0.5 ) 2 Te 3 of different thickness were deposited on glass substrate by the flash evaporation method in a vacuum of 1 × 10 − 5 Torr. X-ray diffraction and transmission electron microscope analysis indicates that these films are polycrystalline even in the asdeposited state and the post-deposition annealing leads to grain growth. Electrical resistivity studies were carried out on these films as a function of temperature (300-450 K) and film thickness (450-2000 Å). Temperature dependence of electrical resistivity shows that (Bi 0.5 Sb 0.5 ) 2 Te 3 films are semiconducting. It is found that electrical conduction activation energy decreases with increase of film thickness and this observation is explained based on the Slater model. Thickness dependence of electrical resistivity is analyzed using the effective mean free path model of size effect with perfect diffuse scattering. This analysis leads to the evaluation of the important physical parameters i.e., mean free path and bulk resistivity of hypothetical bulk.

Microstructure development and fracture toughness of Si3N4 composites were studied in the presence of seeds and Al2O3 + Y2O3 as sintering aids. The elongated β-Si3N4 seeds were introduced into two different α-Si3N4 matrix powders; one was the ultra fine powder matrix and the other was the coarse powder matrix. The amount of seeds varied from 0 to 6 wt%. The grain growth inhibition and the mechanism of toughening were discussed and correlated with microstructure. The maximum fracture toughness of 9.0 MPa m1/2 was obtained for ultra fine powder with 5 wt% seeds hot pressed at 1,700 °C for 6 h.

Room temperature multiferroic electroceramics of Gd doped BiFeO 3 monophasic materials have been synthesized adopting a slow step sintering schedule. Incorporation of Gd nucleates the development of orthorhombic grain growth habit without the appearance of any significant impurity phases with respect to original rhombohedral (R3c) phase of un-doped BiFeO 3. It is observed that, the materials showed room temperature enhanced electric polarization as well as ferromagnetism when rare earth ions like Gd doping is critically optimized (x ¼0.15) in the composition formula of Bi 1 þ 2x Gd 2x/2 Fe 1 À 2x O 3. We believe that magnetic moment of Gd þ 3 ions in Gd doped BiFeO 3 tends to align in the same direction with respect to ferromagnetic component associated with the iron sub lattice. The dielectric constant as well as loss factor shows strong dispersion at lower frequencies and the value of leakage current is greatly suppressed with the increase in concentration of x in the above composition. Addition of excess bismuth and Gd (x ¼ 0.1 and 0.15) caused structural transformation as well as compensated bismuth loss during high temperature sintering. Doping of Gd in BiFeO 3 also suppresses spiral spin modulation structure, which can change Fe-O-Fe bond angle or spin order resulting in enhanced ferromagnetic property.

Pure Y2O3 and Y2O3-ZrO2 solid solutions have been prepared by melt atomization and by pyrolysis of nitrate solutions. Extended solubility is readily achieved in both techniques for the entire composition range investigated: melts with 0.30% ZrO2 and precursors with 0.50% ZrO2. However, solidification of under cooled droplets yields almost exclusively single phase powders with the structure of cubic yttria (D5(sub 3)). In contrast, the pyrolysis route leads to a sequence of metastable microstructures beginning with a nanocrystalline disordered fluorite-based (C1) solid solution. Further heating leads to the evolution of much larger (micron size) flake crystals with a (001) texture, concurrent with partial ordering of the oxygen ions to the sites occupied in the D5(sub 3) addition.

Microstructure development in Sb2O3-doped ZnO was studied to evaluate the influence of inversion boundaries (IBs) on ZnO grain growth. In general, the addition of Sb2O3 is believed to inhibit the ZnO grain growth via the formation of spinels and IBs, but we have shown that even the conditions of exaggerated grain growth can be created in this system. We designed an experiment for diffusional doping of ZnO under slightly increased partial pressure of Sb2O3. In the high-concentration regime we observed no spinels, and yet the ZnO grains were small and inhibited in growth, while in the low-concentration regime we found huge grains, several times larger than normal ZnO grains, showing an obvious exaggerated growth. By controlling the number of nuclei with IBs we can design coarse-grained microstructures even with Sb2O3 doping, which has far-reaching implications in the production of low-voltage varistor devices.

During welding, structures are subjected to localized heating and cooling cycles, as described in Part I.[1] A mathematical model is proposed to determine the metallurgical changes that occur in austenitic stainless steel due to the welding thermal cycle. The proposed kinetic model computes the austenite grain growth as a function of time and temperature. It is based on a Zener pinning grain growth model. The results obtained indicate that the model is in good agreement with the experimental data reported in the literature. Furthermore, it was observed that rewriting the kinetic constant in the grain growth equation as a function of the peak temperature led to improved results for the majority of the cases examined.

The pinning effect of second phase particles on grain growth was simulated by 2-D Monte Carlo simulations. A new variable, the degree of contact between grain boundaries and second phase particles, was introduced to predict the grain size limit in the presence of second phase particles. The modified Zener pinning model containing this new variable can be expressed as: Dr

This paper reports on structural characterization and morphology of titanium dioxide (TiO 2 ) nanofibers prepared by electrospinning using a solution that contained poly(vinyl pyrrolidone) (PVP) and titanium(diisoproproxide) bis(2,4-pentanedionate) 75 wt.% in 2-propanol. TiO 2 nanofibers with diameters of 80-100 nm were successfully obtained from calcination of the as-spun TiO 2 /PVP composite nanofibers at above 300 • C in air for 3 h. The as-spun and calcined TiO 2 /PVP composite nanofibers were characterized by TG-DTA, Raman spectroscopy, XRD, SEM, AFM, and TEM. The results indicated a significant effect of calcination temperature on the crystalline phase in the form of either anatase or mixed anatase-rutile and the morphology of the nanofibers. The anatase-to-rutile transformation and the grain growth during the calcination of the electrospun TiO 2 /PVP composite nanofibers, as revealed by TEM, occurred simultaneously and affected each other. The rutile content was the highest (∼80%) at 800 • C, and it can be expected that the complete anatase-to-rutile transformation in the TiO 2 nanofibers would be above 800 • C.

Polysilicon films were deposited in an epitaxial batch reactor at a high deposition rate. The effect of the deposition temperature, total pressure, source gas flow and in situ doping on the deposition rate and morphological and electrical propertics of these films was studied. Layers with thicknesses up to 12 urn were deposited on a sacrificial oxide covered with a thin polysilicon nucleation layer, which was formed in a low pressure chemical vapour deposition reactor. The thick polysilicon layers were characterized in terms of the surface roughness, grain growth and concentration and distribution of dopants. The residual stress and stress gradient were also determined.

Supersaturated nanocrystalline (16-19 nm) Cu 50 Ag 50 and Cu 70 Ag 30 solid solutions are synthesized by high-energy ball milling. Varying the milling time fcc solid solutions with different lattice parameters are obtained. Thus an increase of the lattice constant that levels off after 20 h of milling is registered for the Cu 50 Ag 50 solid solution. At the same time broad overlapped exothermic effects in the temperature range of 170-370 • C are detected by DTA. These can be associated mainly with solid solution decomposition and a grain growth process. Electrochemical selective dissolution reveals a quasi-critical potential of Cu dissolution in Cu 70 Ag 30 that is shifted 40 mV positively, compared to the dissolution potential of pure Cu, thus ascertaining the Cu (Ag) solid solution formation. The linear area development with the in-depth progress of the Cu dissolution front confirms the dealloying applicability for fabrication of nanoporous Ag structures in this case.

Cellular structures or tessellations are ubiquitous in nature. Metals and ceramics commonly consist of space-filling arrays of single-crystal grains separated by a network of grain boundaries, and foams (froths) are networks of gas-filled bubbles separated by liquid walls. Cellular structures also occur in biological tissue, and in magnetic, ferroelectric and complex fluid contexts. In many situations, the cell/grain/bubble walls move under the influence of their surface tension (capillarity), with a velocity proportional to their mean curvature. As a result, the cells evolve and the structure coarsens. Over 50 years ago, von Neumann derived an exact formula for the growth rate of a cell in a two-dimensional cellular structure (using the relation between wall velocity and mean curvature, the fact that three domain walls meet at 120u and basic topology). This forms the basis of modern grain growth theory. Here we present an exact and much-sought extension of this result into three (and higher) dimensions. The present results may lead to the development of predictive models for capillarity-driven microstructure evolution in a wide range of industrial and commercial processing scenarios-such as the heat treatment of metals, or even controlling the 'head' on a pint of beer.

The heat affected zone (HAZ), has a great influence on the properties of welded joints since it can alter the microstructure and residual stresses. In this paper, the effect of welding parameters and heat input on the HAZ and grain growth has been investigated. The role of grain size on hardness and toughness of low carbon steel has also been studied.

The effects of ZnO addition on structure, microstructure and dielectric properties of (K 0.44 Na 0.52 Li 0.04 )(Nb 0.86 Ta 0.10 Sb 0.04 )O 3 ceramics (KNL-NTS) are investigated. Doping provokes phase segregation, evidenced by the appearance of different types of grains and a tetragonal tungsten-bronze secondary phase at high ZnO doping levels. A clear increase of ferroelectric-paraelectric and orthorhombic-to-tetragonal phase transition temperatures with ZnO content is observed. This produces a reduction of the room temperature piezoelectric constants due to the reduction of the tetragonality (c/a) ratio of the KNL-NTS structure.

In order to reduce sintering temperature and prevent adverse dielectric effects, pure BaTiO 3 powder with the addition of Mn-Si-O glass was sintered in the temperature range of 1175-1300°C. Microstructural observation showed that BaTiO 3 grains of the sintered samples only grew from the initial 400 nm to an average of 430 nm between 1175-1275°C for 1 h, or sintered at 1250°C as long as 27 h. Abnormal BaTiO 3 grains are not found in the sintered samples. The microstructure and phase analysis showed that the dielectric properties, tetragonality, and grain growth of BaTiO 3 are closely controlled by the formation of the liquid phase, newly formed Ba 2 TiSi 2 O 8 grains, and Mn solid solution in BaTiO 3 grains.

Sn-Bi solders may be applied for electronic applications where low-temperature soldering is required, i.e., sensitive components, step soldering and soldering LEDs. In spite of their potential to cover such applications, the mechanical response of soldered joints of Sn-Bi alloys in some cases does not meet the strength requirements due to inappropriate resulting microstructures. Hence, careful examination and control of as-soldered microstructures become necessary with a view to pre-programming reliable final properties. The present study aims to investigate the effects of solidification thermal parameters (growth rate -V L and cooling rate -Ṫ L ) on the microstructure of the Sn-52 wt.%Bi solder solidified under unsteady-state conditions. Samples were obtained by upward directional solidification (DS), followed by characterization through metallography and scanning electron microscopy (SEM). The microstructures are shown to be formed by Sn-rich dendrites decorated with Bi precipitates surrounded by a complex regular eutectic mixture, with alternated Bi-rich and Sn-rich phases. Experimental correlations of primary (λ 1 ), secondary (λ 2 ), tertiary (λ 3 ) dendritic and eutectic spacings (λ coarse and λ fine ) with cooling rate and growth rate are established. Two ranges of lamellar eutectic sizes were determined, described by two experimental equations λ = 1.1 V L −1/2 and λ = 0.67 V L −1/2 . The onset of tertiary branches within the dendritic array along the Sn-52 wt.%Bi alloy DS casting is shown to occur for cooling rates lower than 1.5°C/s.

The chief variables of grain growth are temperature and annealing time. Temperature, however, has a greater effect than time because it is tied in with an exponential function. To test if this is true, micrographs of brass samples annealed at varying temperatures and durations of time, were studied. The findings prove that temperature does indeed have a greater effect on the rate of grain growth than time. This may be attributed to enhanced diffusion rate in the alloy. The linear intercept method (or Heyn's method) was used to determine average grain diameters of the various samples. The purpose of sampling (or analysis) was to determine some variables in the grain growth formula (formula 5), that is, the time-independent constant n, activation energy (Q) and material constant k 0 . After calculations, the value of the time-independent constant n is found to deviate from the ideal n value of 2. The calculated value of 4.25 is due to grain growth in the studied brass samples being unideal i.e. the grains are not spherical. The activation energy is found to be 246 kJ and k 0 to be 1.877E24. The resultant formula is then

For example, LF-FSP combustion of metalloorganic yttrium and aluminum precursors in a 3/5 ratio forms hexagonal Y 3 Al 5 O 12 , a newly discovered crystalline phase detailed in this work. The resulting 15-35 nm average particle size, single crystal nanopowders were characterized by TGA-DTA, XRD, HR-TEM, electron diffraction and FTIR. The data was used to establish a model for the crystal structure of this new phase (hexagonal, with crystal parameter of a = 0.736 nm, c = 1.052) consisting of a superlattice of substituted hexagonal YAlO 3 . YAG has been extensively investigated for its applications as scintillators, phosphors and as a laser host. Fully dispersible, unaggregated single crystal YAG nanopowders with average particle sizes of 35-50 nm were obtained from hexagonal Y 3 Al 5 O 12 after annealing at 850°C-1200°C (for 2h-8d). The resulting YAG nanopowder was processed into green bodies using cold isostatic pressing after adding binders. 99% + dense monoliths were obtained after sintering at 1400°C in vacuum (6-8 h), while maintaining grain sizes < 500 nm. The ability to sinter while keeping sub-micron grains differs from present techniques (where translucency is obtained through exaggerated grain growth to 5-10 microns) reported in the literature for sintering polycrystalline YAG. and is the first step for improving polycrystalline YAG laser host optical properties.

The practical application of technology based on superplastic forming combined with diffusion bonding (SPF/DB) to advanced aircraft engine blade manufacturing is investigated in this paper. Four-sheet hollow engine blades, a Ti±6Al±4V sandwich structure, have been fabricated through the SPF/DB process after determining the design dimensions and deformation procedures. Some novel designs and special auxiliary techniques have been developed to facilitate the superplastic SPF/DB process. The ®nished blades can meet the property and pro®le demands, particularly in the boundary region (the leading and the trailing). The effects of the microstructure on the SPF/DB process were discussed. Slight grain growth was observed after the thermal exposure. Tensile tests show a strength reduction of 30% from the as-received sheets to the formed sheets. The microstructures at the interfaces indicate that a bonding ratio of 100% can be reached in most bonding areas. Low bonding ratios in some regions such as cell corners and triple angles were unavoidable. The bonds present in the blade structures can be divided into four types, based on their formation quality characteristics. The distribution in thickness and bonding ratio within a formed cell were investigated, revealing two deformation localization zones and a poor-bonding area. Further processing of the formed structures involves electric spark machining and surface polishing. #

Liquid phase sintering of SiC has been studied using different sintering aids with and without the application of pressure during sintering. After Pressureless Sintering the densification behaviour of the SiC-based powder mixtures was observed to be markedly dependent not only on the type and amount of sintering aids used, but also on the crystal structure of the SiC powder. In contrast, hipping leads to high densities in all cases, independently of the chemical composition of the mixture and the type of SiC powder used. When carbon was added to these compositions, fully dense materials were still obtained. However, a pronounced grain growth was observed. Compositions containing additions of SiO 2 and Y 2 O 3 did not show any densification after pressureless sintering, due to the high viscosity and extensive volatilisation of the liquids formed at the sintering temperature. On the other hand, fully dense specimens obtained after hiping contained crystalline intergranular phases, which turned to a vitreous structure, as Al 2 O 3 was included as a third component. #

We have introduced a novel approach to enhance the perovskite solar cell efficiency by controlling the grain growth and light harvesting properties of perovskite crystallites. Instead of using a mesoporous TiO 2 layer, we have modified the surface microstructuring of the TiO 2 film by dispensing nano assembled TiO 2 submicron structures (nanobeads, NBs) on TiO 2 compact layer. With this new approach solar cell efficiency was improved significantly through an increase in both J sc and V oc . This high efficiency is attributed to crystallite size of the perovskite phase. These also act as light scattering centers giving higher current density and reduced recombination effects giving higher open circuit voltage.

The densification behaviour, microstructural development and mechanical properties of a 5 vol.% silicon carbide dispersed alumina nanocomposite were studied by incorporating six different oxide dopants (1 wt.%). It was found that MgO, Y 2 O 3 and CeO 2 enhanced the densification of the nanocomposite, which can be explained by a liquid phase assisted sintering process. The yttriadoped nanocomposite could be pressureless sintered at 1550 C. Doping with MgO or CeO 2 refines the grain size of the matrix alumina whereas yttria addition induces exaggerated grain growth. The Young's modulus, hardness, fracture toughness and erosive wear resistance were evaluated. Doped nanocomposites exhibit slightly lower Young's modulus and higher hardness values than that of the undoped nanocomposite. CeO 2 doping improves hardness and fracture toughness slightly whereas the improvement in erosive wear resistance was 2.5 times higher than the other nanocomposites. Improvements in properties are explained in terms of residual compressive stresses, grain refinement and grain boundary strengthening. #

Under Mediterranean environments, farmers usually prefer to sow barley rather than wheat as it is generally believed that barley yields more under stressful conditions. As terminal stresses such as high temperature and water are common constraints in Mediterranean regions, higher grain weight stability may confer a clear advantage in order to maintain higher yields. The objective of the present study was to compare the stability in terms of grain weight and its components for barley, bread wheat, and durum wheat, exploring a wide range of nitrogen and water availabilities in experiments conducted in a Mediterranean region. Grain weight ranged from 23.8 to 47.7 mg grain −1 , being higher for durum wheat than barley and bread wheat. Durum wheat presented higher variability both in maximum grain filling rate and duration of grain filling period than bread wheat or barley. The three species responded similarly in terms of grain nitrogen content to changes in the environmental conditions explored. It is concluded that in terms of grain weight barley is as stable as bread wheat. However, durum wheat presented a lower stability than barley and bread wheat.

Neodymium (Nd) doped barium titanate powder (Ba (1-x) Nd x TiO 3 ) with x value varying from 0, 0.01, 0.03, 0.05, 0.07, 0.10 and 0.13 was prepared using the sol gel method. The powder samples were calcined at 700°C and tetragonal phase appeared in the powders before they were sintered at 1250°C for 3 h. The undoped samples have a polycrystalline tetragonal structure, but Nd doping into the BaTiO 3 caused phase transformation from tetragonal to cubic. The smaller grains (0.35 lm) produced with the addition of Nd is associated to the inhibition of grain growth of samples. The powders for each composition were pressed into pellets and tested as dielectric resonator antenna (DRA). It was found that on the actual antenna circuit, each sample showed a resonance frequency at X-band application and a dielectric constant value in the range of 51.25-56.89 and tangent loss was 0.039-0.045, depending on the concentration of the Nd at room temperature.

In the current work, liquid feed flame spray pyrolysis (LF-FSP) was used to create three novel nanopowders in the Y2O3-Al 2O3 system: alpha-Al2O3, YAG (garnet Y3Al5O12) and hexagonal Y3Al 5O12. For example, LF-FSP combustion of metalloorganic yttrium and aluminum precursors in a 3/5 ratio forms hexagonal Y3Al5O 12, a newly discovered crystalline phase detailed in this work. The resulting 15-35

The development of texture and microstructure in two kinds of conventional grain oriented electrical steels, which were annealed at different primary annealing temperature, were investigated. The specimens were analyzed using Orientation Distribution Function (ODF), optical microscopy and OIM (Orientation Imaging Microscopy). The size distributions of AlN precipitates, which were used as grain growth inhibitors, were investigated using transmission electron microscope (TEM) and an image analyzer. The influence of primary annealing conditions on the secondary recrystallization in conventional grain oriented electrical steels was discussed based on information on precipitate distributions and the kinetics of abnormal grain growth of Goss grains. When the high energy boundary theory and the driving force for the Goss grain growth are considered, it is possible to explain the reason for significant improvement of the final texture and magnetic properties in the specimen that was recovered before the final annealing compared to the specimen that was recrystallized. 

This work is devoted to the kinetic study of densification and grain growth of LaPO 4 ceramics. By sintering at a temperature close to 1500 8C, densification rate can reach up to 98% of the theoretical density and grain growth can be controlled in the range 0.6-4 mm. Isothermal shrinkage measurements carried out by dilatometry revealed that densification occurs by lattice diffusion from the grain boundary to the neck. The activation energy for densification (E D ) is evaluated as 480 AE 4 kJ mol À1 . Grain growth is governed by lattice diffusion controlled pore drag and the activation energy (E G ) is found to be 603 AE 2 kJ mol À1 . The pore mobility is so low that grain growth only occurs for almost fully dense materials. #

Piezoelectric Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (PMN-PT) ceramics with 0.2 and 0.35 PT have been prepared from mechanochemically activated powders. Pressureless sintering in air and hot pressing were tested. PbZrO 3 packing was necessary to limit lead oxide losses and to avoid the formation of second phases at the surface when temperatures above 1000 C were used. Ceramics sintered at 1200 C presented densities of 90% and a grain size of 4 mm. Hot pressed ceramics hardly showed porosity and had submicron (0.1-0.5 mm) grain size, which make the mechanoactivated powders very suitable for templated grain growth matrices. Electrical and electromechanical characterisation was accomplished. The 0.2 PT composition combined relaxor dielectric behaviour with piezoelectricity after poling. The 0.35 PT ceramics presented a first order ferroelectric-paraelectric transition at 171 C and a complex transverse piezoelectric coefficient of À(181.8-i3.6) pC N À1 at room temperature. #

Addition of 0.5 mol% of CoO into SnO 2 promotes densi®cation of this oxide to 99% of the theoretical density during sintering. TEM in this system reveals that after sintering at 1210 C a secondary phase of Co 2 SnO 4 is precipitated at the SnO 2 grain boundaries during cooling. This phase is formed by diusion of Co ions from the bulk to the grain boundary during sintering leaving needle-like defects at the grain bulk. The high resolution TEM micrograph of this system sintered at 1210 C and 1400 C showed an amorphous grain boundary region low in cobalt, indicating that the Co 2 SnO 4 phase is precipitated from this region. #

The code DIONISIO 1.0 describes most of the main phenomena occurring in a fuel rod throughout its life under normal operation conditions of a nuclear thermal reactor. Starting from the power history, DIONISIO predicts the temperature distribution in the domain, elastic and plastic stress and strain, creep, swelling and densification, release of fission gases, caesium and iodine to the rod free volume, gas mixing, pressure increase, restructuring and grain growth in the UO 2 pellet, irradiation growth of the Zircaloy cladding, oxide layer growth on its surface, hydrogen uptake and the effects of a corrosive atmosphere either internal or external. In particular, the models of thermal conductance of the gap and of pellet-cladding mechanical interaction incorporated to the code constitute two realistic tools. The possibility of gap closure (including partial contact between rough surfaces) and reopening during burnup is allowed. The non-linear differential equations are integrated by the finite element method in two-dimensions assuming cylindrical symmetry. Good results are obtained for the simulation of several irradiation tests.

1 Introduction Spintronics is gaining popularity because of the interesting physical phenomena that can be observed in these systems as well as due to the potential applications that can be derived from it. While the magnetic read sensors of the hard disk drive are already beneficiaries of the early development in spintronics, the magnetic random access memory (MRAM), magnetic logics, spin-transistors, and quantum computing are some of the exciting possibilities that may arise from the outcome of further spintronics research. Out of the several emerging applications, MRAM is given a stronger industrial emphasis due to the several advantages it offers over other competing memory/storage class memory. Moreover, the recent developments in the spin-transfer torque (STT) induced switching of magnetization have provided more excitement and realistic possibilities of MRAM being a strong candidate for future memory applications. This article provides an overview of MRAM with a particular emphasis on materials with perpendicular magnetic anisotropy (PMA) for this application.

Self-annealing of electro-chemically deposited copper films is described and studied, with a focus on the effect of process parameters like concentration of the organic additives, current density or thickness of plated copper. Sheet resistance and stress have been monitored and a non-correlated behavior has been observed for these two film characteristics, indicating that other phenomena than the grain growth typically associated with the room temperature recrystallization are likely to be involved. Diffusion/desorption of carbon containing molecules incorporated in the copper film from the bath additives could be a mechanism for stress release.

The calcining and sintering behaviour of fluorapatite synthesised by precipitation has been studied. During the calcination process, in the temperature range 400-9008C, the specific surface area decreases with a rise in temperature. Below 7158C, the decrease is associated with grain growth according to a superficial diffusion mechanism. Above this temperature, several mechanisms may take part in the coarsening. Sintering of fluorapatite is performed between 690 and 13208C, under an argon atmosphere when the gas atmosphere is not fittingly dried; hydroxyfluorapatite can be formed during sintering. Densification appears to be governed by grain growth. At moderate temperatures coarsening leads to dense bodies. A relative density of about 97% is obtained at 10208C. Above 11008C densification is hindered by coarsening which becomes important and much quicker when the liquid phase is formed at 11808C.

In the present work, Cu-Al-Ni shape memory alloy strips were prepared successfully from premixed elemental Cu, Al, and Ni powders in the ratio 82:14:4 (wt pct) by a novel processing route consisting of preparing powder preforms, sintering, and unsheathed hot rolling of the sintered preforms. Subsequently, the hot rolled strips were homogenized. The as-rolled strips consisted of two phases-a and b¢. A postconsolidation homogenization of the hot rolled strips was carried out at 1173 K (900°C) for different time periods. It has been shown that a homogenization period of 4 hours was sufficient to achieve a single-phase material consisting of only martensitic phase. It also has been shown that the 4-hour homogenized and quenched Cu-Al-Ni shape memory alloy strips primarily consisted of self-accommodated b¢ martensite plates, which are necessary for realizing shape memory effect (SME). The finished hot rolled Cu-Al-Ni strips had a fracture strength of 476 MPa, coupled with 2.5 pct elongation. The shape memory tests showed almost 100 pct recovery after 10 thermomechanical cycles in the hot rolled strips at 1 pct and 2 pct prestrain level.

Nanocrystalline (Y 0.7 Gd 0.3 ) 2 O 3 powder, synthetised via polymer complex solution method, was compacted into 25 pellets applying high pressures (173-867 MPa) for 30 s that were subsequently sintered at different temperatures (800-1400 8C) for 18 h. The morphology and optical characteristics of the starting powder and prepared ceramic samples were monitored and discussed in order to identify the changes induced with the variations of initial compacting pressure, which influence is often neglected, and with sintering temperature. The grain size tends to decrease significantly with increasing pressure, even when elevated temperatures are used for annealing, while low compacting pressure resulted in grain coarsening and, in some cases, even in anomalous morphology of ceramic samples. Luminescence emission in ceramic samples decays faster than in nanopowders, that is in complete agreement with the grain formation and gradual transformation to the bulk material. Judd-Ofelt intensity parameters and branching ratios were calculated taking into account the difference in effective refractive index for nanopowder and ceramic samples. #