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Dielectric, X-ray, Mossbauer and magnetization studies of (1 − x)PbFeTaO-( x)PbTiO ceramics with 0 ≤ x ≤ 0.3 have been carried out to determine the compositional evolution of ferroelectric and magnetic phase transition temperatures. Addition of PbTiO to PbFeTaO increases the temperature T of the dielectric permittivity maximum, decreases both the diffusion of this maximum and its frequency dependence. However, the Curie-Weiss temperature exceeds T for all the compositions studied, indicating that the phase transition still remains diffused. Dilution of the (Fe, Ta)-sublattice by Ti lowers the Neel temperature T but above a certain compositional threshold ( x ≈ 0.1) fast lowering of T stops and a new magnetic state stable in a rather wide compositional range appears. Large difference between the zero-field-cooled (ZFC) and FC magnetization-temperature curves as well as between the temperatures of magnetic phase transition determined from Mossbauer and magnetization studies for compositions with x > 0.1 implies that this state is a spin-glass phase. [ABSTRACT FROM AUTHOR]

Diffusion of the 4d transition elements in Ni has been investigated within the five-frequency model framework using migration energy barriers calculated from the first principles. Agreement with counterintuitive experimental/calculated data is observed; atoms in the middle of 4d row have the smallest atomic radii while exhibiting the lowest diffusivity as compared to larger atoms at the beginning and the end of 4d row. We show that 4d solute diffusion is controlled mainly by the size misfit. The larger atoms have higher solute-vacancy binding energies and lower migration barriers. Both were shown to correlate with a displacement of the equilibrium solute position toward the adjacent vacancy. The difference in mechanisms controlling sp- and transition elements diffusion rates in Ni is discussed. [ABSTRACT FROM AUTHOR]

Sn-20.0 wt%In (Sn-20.0In) alloy is a promising base material in Pb-free solders for low-temperature applications. Zn is often used as an additive to Pb-free solders to reduce the extent of undercooling during reflow. Cu is the most commonly used substrate in electronics industry. Interfacial stability at Sn-In-Zn/Cu joints is crucial to reliability of electronic products. In this study, interfacial reactions between Sn-20.0 wt%In- x wt%Zn (Sn-20.0In- xZn) solders and Cu where x = 0.5, 0.7, 1.0, 2.0, 3.0, and 5.0 at 150, 230, and 260 °C were experimentally examined. It is found that the reaction phase formation and interfacial morphologies are strongly influenced by Zn concentrations. The reaction phases evolve from the CuSn phase, CuZn and CuZn phase, to CuZn phase with higher Zn doping in the solders. The CuZn phase acted as a diffusion barrier and suppressed the growth of the CuSn phase. The results indicate that 2.0 wt%Zn addition resulted in the gentlest reactions during both soldering and solid-state ageing in Sn-20.0In- xZn/Cu couples. [ABSTRACT FROM AUTHOR]

An analytical model for dissolution kinetics of secondary phase particles upon isothermal annealing has been proposed. Considering the interactions of solute diffusion fields in front of the secondary phase/matrix interface upon dissolution, a Johnson-Mehl-Avrami type equation, subjected to necessary modification, was derived, in combination with a classic dissolution model for single-particle system. Compared with the semiempirical dissolution models, which are used to fit the experimental results and phase-field method simulation, the current model follows an analogous form, but with the time-dependent kinetic parameters. Distinct from the model fitting work published recently, the current model is derived from the diffusion-controlled transformation theory, while the modeling quality is guaranteed by the physically realistic model parameters. On this basis, the current model calculation leads to a clear relationship between the secondary phase volume fraction and the time. Accordingly, model predictions for isothermal θ′ dissolution in Al-3.0wt%-Cu alloy and silicon dissolution in Al-0.8wt%-Si alloy were performed; good agreement with the published experimental data has been achieved. [ABSTRACT FROM AUTHOR]

The soft impingement effect at the later stage of partitioning phase transformations has been modeled both for the diffusion-controlled growth model and for the mixed-mode model. Instead of the linear and exponential approximations for the concentration gradient in front of the interface used in the past, a general polynomial method of dealing with the diffusion field is proposed. The linear and exponential diffusion field approximations are two specific cases of the polynomial diffusion field approximation. The effect of soft impingement on the overall partitioning phase transformation is only related to the degree of the super-saturation in case of the diffusion-controlled growth model, while it is determined by both the growth mode and the degree of super-saturation in case of the mixed-mode model. [ABSTRACT FROM AUTHOR]

This paper presents a simple technique for preparation of yttria-doped ceria (YDC) coated tetragonal zirconia polycrystal (3Y-TZP) powder and its phase development upon firing. The coating solution was prepared using yttrium nitrate hexahydrate and cerium nitrate hexahydrate as starting reagents. Thermochemical reactions of the coated powder were studied using TGA and FTIR while phase development upon firing was examined using XRD. Inward diffusion of the coating YDC into the TZP particles was monitored by observing the change of crystal structure and lattice parameter as a function of sintering temperature and time. At sintering temperature of 1300 °C for 1 h, crystal structure of the sample was still tetragonal (t-ZrO2). Increasing sintering time to 5 h at 1300 °C, diffusion of YDC into TZP particles occurred drastically and the structure was changed to cubic (c-ZrO2) as indicated by the disappearance of (002)/(200) peak splitting. Increasing sintering temperature to 1400 and 1500 °C, however, resulted in the co-existence of tetragonal and cubic phases as indicated by the appearance of triples around 72.5–74° 2 θ and also the decrease of cubic lattice parameter. When the sintering temperature was further increased to 1600 °C, lattice parameter was only slightly changed, suggesting that inward diffusion of YDC reached saturation point around this temperature. [ABSTRACT FROM AUTHOR]

Spark Plasma sintering (SPS) technique allows powders to be compacted at low temperature with a very short holding time. The powder loaded into a carbon die is heated via direct current pulses and simultaneously submitted to an uni-axial pressure of several MPa. Full density of the sample is achieved within minutes. This process is used to study Cu and Ag metals interactions with V2O5 oxide. Syntheses of M x V2O5 phases (M = Cu, Ag) have been achieved within minutes. Thus Cu and Ag atoms penetrate microcrystals of V2O5 oxide at a high speed, shearing its crystal network and simultaneously rebuilding the crystal structures of the prototype networks β, β′, ε or δ M x V2O5. To account for the formation of these phases identified by X-ray diffraction, structural mechanisms are proposed. Cu and Ag atomic diffusion parameters have been determined from energy dispersive X-ray spectroscopy (EDX) and electron micropobe analysis (EPMA) line scans. High values of diffusion coefficients have been determined. Cu atoms diffuse faster than Ag, D Cu ≈ 4 × 10−8 m2/s and D Ag ≈ 0.5–1 × 10−9 m2/s in ε and δ M x V2O5 phases, respectively. Their formation may also be used as a model for further investigations into the diffusion mechanisms of atoms in solids and for a better understanding of the SPS process. [ABSTRACT FROM AUTHOR]

The effect of pulsed DC current on the atomic diffusion of an Nb–C system using Spark Plasma Sintering (SPS) was investigated. In all experiments, a current density of approximately 723 A/cm2 was applied to the specimen and used in a temperature range of 1,673–1,973 K. From the results of X-ray diffraction analysis, the product phases formed between Nb and C were found to be Nb2C and NbC. The growth of product layers significantly increased in the presence of current. However, the thickness of the product layer did not change in the current direction in the SPS. The activation energies for the formation of the Nb2C and NbC layers were calculated to be 298 ± 4 kJ/mol and 282 ± 3 kJ/mol in the presence of current, which were similar values compared to the activation energies of 300 ± 5 kJ/mol and 285 ± 2 kJ/mol in the absence of current, respectively. [ABSTRACT FROM AUTHOR]

This article discusses crystal rotations in micro-compressed single copper columns that are dislocation-induced. Although flow stress of such single crystal compression samples has been found to be size dependent through the use of a focused ion beam, no model has been proposed to explain this unusual behavior. Experiments with dislocation starvation, surface image stresses, and consideration of stochastic single-ended dislocation sources have also failed to develop a model. This study applies an in situ set-up for the loading experiments and, subsequently, local crystal orientation of the deformed samples is analyzed by electron backscatter diffraction to examine the microstructural development.

This work deals with the development of Mg-based alloys with enhanced properties at elevated temperatures. This is achieved by precipitation of binary phases such as MgZn2 and Mg2Sn during the aging of these alloys. The aim of the present work is to develop and calibrate a model for precipitation hardening in Mg-based alloys, as different types of precipitates form simultaneously. The modified Langer-Schwartz approach, while taking into account nucleation, growth and coarsening of the new phase precipitations, was used for the analysis of precipitates’ evolution and precipitation hardening during aging of Mg-based alloys. Two strengthening mechanisms associated with particle-dislocation interaction (shearing and bypassing) were considered to be operating simultaneously due to particle size-distribution. Parameters of the model, R N i and k σ i , were found by fitting of calculated densities and average sizes of precipitates with ones estimated from experiments. The effective diffusion coefficients of phase formation processes, which determine the strengthening kinetics, were estimated from the hardness maximum positions on the aging curves. [ABSTRACT FROM AUTHOR]

The role of grain boundary constraint in strain localization and concomitant constitutive response was examined by performing a series of uniaxial compression tests on a tantalum bicrystal. Tantalum single crystals were diffusion bonded to form a (011) 90^∘ twist boundary that was compressed along the common [011] direction. The plastic deformation resulted in the creation of deformation bands away from the highly constraining grain boundary, resembling those bands known from single crystal plastic deformation. Near the grain boundary, such deformation band formation could not be detected. Instead a distinctive pattern of crystal lattice rotation was observed that filled a rather large volume (several millimeters in size) around the bicrystal grain boundary. The internal deformation band structure as well as the crystal lattice rotation pattern near the bicrystal grain boundary were characterized and found to give greater rates of work hardening in the neighborhood of the grain boundary. [ABSTRACT FROM AUTHOR]

Nanosized solid Pb inclusions in Al have fcc structure and perfect cuboctahedral shape. When the inclusions melt they attain a rounded equilibrium shape and due to the low miscibility between the two elements, the liquid inclusions are retained as individual nanosized droplets located inside the solid Al matrix. As the temperature is increased the smaller liquid Pb inclusions are observed to move in a three-dimensional random walk over distances that can be orders of magnitude larger than their size. Inclusions attached to dislocations exhibit a similar type of random walk confined to long-distance one-dimensional movement along the dislocation lines and short-range two-dimensional vibrations perpendicular to the dislocation lines. The diffusion coefficients of the moving inclusions can be obtained from an Einstein-Smoluchowski analysis of the inclusion traces providing input for information on the mechanisms responsible for the movements. [ABSTRACT FROM AUTHOR]

The diffusion coefficients of carbon and titanium in γ -iron were measured in a 6T magnetic field and in magnetic field gradients ranging from 30 to 45 T/m. We have found that the diffusion of carbon in γ -iron is retarded by application of a 6T magnetic field. In contrast with carbon diffusion, no noticeable effect of a magnetic field on the diffusivity of titanium in γ -iron is observed. On the other hand, the diffusion of carbon in γ -iron can be enhanced in a magnetic field gradient when carbon atoms move towards the direction with a higher magnetic field strength. The higher the magnetic field gradient strength becomes, the more the carbon diffusion is enhanced. Nevertheless, a magnetic field gradient causes a decrease in diffusivity of carbon in γ -iron when the opposite magnetic field gradient is applied. [ABSTRACT FROM AUTHOR]

Simultaneous growth of solid and gas phases from gas supersaturated melt is the basis of a relatively new method for the production of ordered porosity materials. Such phase transformation is called gas-eutectic reaction. The structure obtained mainly depends on thermal and gas diffusion phenomena at solid/liquid interface. It is difficult to control this phase transformation but it is very important to the eventual structure. The development of a general mathematical model of the entire physical process will help for better understanding of the structure formation and will allow effective control to be provided. This paper presents a mathematical description of the complex physical phenomena during gas-eutectic transformation. Analyses for heat transfer, solidification kinetics and gas diffusion were coupled to describe the formation of the gas reinforced structure. The model was applied for simulation of structures after some special processing regimes. The structure sensitivity with respect to the different components of gas pressure is discussed. [ABSTRACT FROM AUTHOR]

Diffusion in material of inhomogeneous composition can induce phase changes, even at a constant temperature. A transient liquid phase (TLP), in which a liquid layer is formed and subsequently solidifies, is one example of such an isothermal phase change. This phenomenon is exploited industrially in TLP bonding and sintering processes. Successful processing requires an understanding of the behaviour of the transient liquid layer in terms of both diffusion-controlled phase boundary migration and capillarity-driven flow.In this paper, a numerical model is presented for the simulation of diffusion-controlled dissolution and solidification in one dimension. The width of a liquid layer and time to solidification are studied for various bonding conditions. A novel approach is proposed, which generates results of a high precision even with coarse meshes and high interface velocities. The model is validated using experimental data from a variety of systems, including solid/solid diffusion couples. [ABSTRACT FROM AUTHOR]

Solid state spreading of copper particles on a copper polycrystalline substrate was analysed at 1050°C. A specific procedure was settled to produce pure monocrystalline and nearly spherical copper particles. Spreading dynamics were analysed from SEM images and preferential particle/substrate orientations were identified by EBSD. The effect of a preferential orientation on the spreading kinetics is limited, if any. A general agreement is found between the kinetic results and numerical calculations of Mullins [1] for mass transport by surface diffusion under the action of surface curvature gradients. The experimental kinetics are however significantly more rapid, due to the contribution of other mechanisms like volume diffusion. [ABSTRACT FROM AUTHOR]

The peritectic transition, where d -ferrite and liquid transform into ? -austenite, is an important aspect of product quality and process control in many ferrous and non-ferrous alloys. Due to the high temperatures at which the transition takes place, relatively little experimental work has been carried out to quantify the underlying phenomena. This paper presents recent work in visualizing the peritectic reaction stage of the transition. The visualization was carried out on the surface of hyperperitectic Fe-4.7 wt% Ni samples using a Confocal Scanning Laser Microscope (CSLM) equipped with a gold-image furnace. The focus of the research is to quantify the rate and shape evolution of the ? -austenite phase as it envelopes the d -ferrite grains. Tip radii of 8 and 5 µ m were witnessed and it was found that, as these tips approached one-another their shape was altered and their growth rates decreased due to soft impingement of their respective diffusion fields. Comparing the separation distance at the point of soft impingement with the tip radius suggested a proportionality constant between tip radius of curvature and diffusion field size of between 1.1 and 1.3. [ABSTRACT FROM AUTHOR]

Grain growth of ZnO during liquid-phase sintering of binary ZnO-V2O5 ceramics has been studied for V2O5 contents from 0.5 to 4 mol% and sintering from 900°C to 1200°C. The results are discussed and compared with previous studies in terms of the phenomenological kinetic grain growth expression: Gn - Gon = Kot exp(-Q/RT). Addition of V2O5 is found to decrease the ZnO grain growth exponent, n, as well as the apparent activation energy, Q. The activation analysis also reveals a change in the rate-controlling mechanism for ZnO grain growth. Following a low-V2O5-content (≤2 mol%) of nearly constant Q values of about 88 kJ/mol, further V2O5 additions cause an increase of the Q value to about 115 kJ/mol. Consistent with accepted models of liquid-phase sintering, it is concluded that the rate-controlling mechanism of ZnO grain growth during liquid-phase sintering in the presence of V2O5 changes from one of a phase-boundary reaction at low V2O5 levels to one of diffusion through the liquid phase at more than 2 mol% V2O5 levels. [ABSTRACT FROM AUTHOR]

A theoretical model of grain growth in sintering of clustered powder compacts is outlined, showing that the microstructure evolution is stepwise continuous in time and its general trends can be predicted independently of the particular system and process being considered. The dependence of coarsening on densification can be accounted for by introducing a densification-scaled time variable (intrinsic time). The theory is successively applied to systems where particular local mechanisms of matter transport are supposed to operate, respectively in the initial/intermediate and the intermediate/final stage of sintering. The obtained mathematical models are solved numerically to follow the evolution of three regularly packed clusters. The model predictions are in good agreement with experimental data obtained by other researchers. [ABSTRACT FROM AUTHOR]

Studies the lattice variation and thermal parameters of pure and impurity-added calcium tartrate tetrahydrate crystals. Estimation of the Debye temperatures using semiempirical relations; Performance of test tube diffusion method in growing calcium tartrate single crystals in a gel medium; Analysis of thermal parameters for pure and impurity added calcium tartrate tetrahydrate crystals.