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We model electrodeposition using a formalism developed to describe nucleation and growth processes. In particular, we calculate non-equilibrium, equal-time correlation functions that capture the kinetics of electrodeposition (with particular application to elemental metals) and highlight the evolving correlation lengths and associated roughness in a growing electrodeposited film. These results are interpreted for the case of diffusion-limited growth at late times and, via a phase-field model, for the case of interface-controlled growth. Finally, we discuss the analysis of experimental deposition data using the formalism outlined here and demonstrate that important kinetic information may be readily extracted. [ABSTRACT FROM AUTHOR]

Abstract: Grain growth experiments on thin metallic films have shown the geometric and topological characteristics of the grain structure to be universal and independent of many experimental conditions. The universal size distribution, however, is found to differ both qualitatively and quantitatively from classical curvature driven models of Mullins type, which reduce grain growth to an evolution of a grain boundary network, with the experiments exhibiting an excess of small grains (termed an “ear”) and an excess of very large grains (termed a “tail”) compared with the models. While a plethora of extensions of the original Mullins model have been proposed to explain these characteristics, none have been successful. In this work, large-scale simulations of a model that resolves the atomic scale on diffusive time scales, the phase field crystal model, are used to examine the complex phenomena of grain growth. The results are in remarkable agreement with the prior experimental results, recovering the characteristic “ear” and “tail” features of the experimental grain size distribution. The simulations also indicate that, while the geometric and topological characteristics are universal, the dynamic growth exponent is not. [Copyright &y& Elsevier]

Abstract: The underlying cause of stagnation of grain growth in thin metallic films remains a puzzle. Here it is re-visited by means of detailed comparison of experiments and simulations, using a broad range of metrics that, in addition to grain size, includes the number of sides and the average side class of nearest neighbors. The experimental grain size data reported is large and comprises nearly 35,000 grains from 27 thin film samples of Al and Cu with thicknesses in the range of 25–158nm. The size distributions for the Al and Cu films are remarkably similar to each other despite the many and significant differences in experimental conditions, which include sputtering target purity, substrate type, film thickness, deposition temperature, actual as well as homologous annealing temperatures, annealing time, absolute grain size, and the twin density within the grains. This similarity argues for a universal experimental grain size distribution, which for grain diameters is lognormal as found previously for thin films at stagnation. Comparison of the experimental grain size distribution with that for two dimensional grain growth simulations with isotropic boundary energy shows the distributions to differ in two regions, termed the “ear” and the “tail”. It is shown that the excess small grains in the region of the “ear” are primarily the 3 and 4-sided grains, whereas the excess of large grains in the “tail” region are grains with more than nine sides. The excesses in the ear and tail regions of the experimental distributions are necessarily balanced by a deficiency in the mid-sized grains with 6–8 sides. Five causes are examined to identify the puzzling difference between simulations with isotropic boundary energy and experiments. These are (i) driving forces other than grain boundary energy reduction, (ii) anisotropy of grain boundary energy, (iii) grain boundary grooving, (iv) solute drag and (v) triple junction drag. No single cause is seen to provide an explanation for the observed experimental behavior. However, it is speculated that a combination of causes that include the anisotropy of grain boundary energy will be needed to explain the experimental behavior. [Copyright &y& Elsevier]

Abstract: Relative free energies of 〈111〉 tilt boundaries in 1.7-μm-thick Al films were compared with boundary enthalpies obtained via molecular dynamics simulations. Grain growth studies in 25 and 100-nm-thick Al films were compared with simulations. The sources of the differences between experimental and simulational results are discussed. [Copyright &y& Elsevier]

The impact of 11 alloying elements, namely Mg, Ti, In, Sn, Al, Ag, Co, Nb and B, at two nominal concentration of 1 and 3 at%, and Ir and W, at only a nominal concentration of 3 at%, on the evolution of texture of Cu was investigated. The behavior of the alloy films was compared with that for a pure Cu film. The films were electron beam evaporated onto oxidized Si wafers and had thicknesses in the range of 420–560 nm. Annealing was carried out at 3°C/s to 400°C, 650°C and 950°C. For the lowest annealing temperature, the samples were held isothermally for 5 h, while for the higher annealing temperatures, the samples were cooled immediately after reaching temperature. In all cases, annealing resulted in the strengthening of film texture. For most of the films, the 〈1 1 1〉 component either remained or became the strongest fiber component with the increase in annealing temperature. The interesting exceptions were the two Mg-containing films for which the 〈1 1 0〉 component was the strongest. Whereas in the as-deposited state all alloy films, except the nominally 3 at% Nb film, had weaker textures than pure Cu, certain combinations of alloy concentration and annealing conditions resulted in more strongly textured films when compared with pure Cu. For example, the most strongly textured film after the 400°C and 950°C anneals were, respectively, Cu(Ti) and Cu(Nb), both nominally 3 at%. Film texture was also related to grain growth for the 400°C-annealed films. The behavior of the alloy films is discussed in terms of the various driving and pinning forces for grain growth and texture evolution in thin films. No simple correlations of alloy film behavior with atom size, electronegativity or the binary alloy phase diagram were found. [Copyright &y& Elsevier]

Detailed understanding of the connections between nanostructure and magnetic properties is key to the realization of optimal exchange-spring magnets. To this end, x-ray and electron diffraction and transmission electron microscopy were used to study the evolution of phases, microstructure and texture of model exchange-spring bilayers of L10 - CoPt/Co upon annealing at temperatures ranging from 300–550 °C. The work was motivated by previously—detailed changes in the magnetic exchange coupling of the system induced by the annealing treatments . Unannealed CoPt/Co bilayers comprised a <111> fiber-textured L10 CoPt layer and a <0001> fiber-textured Co layer. The Co layer predominantly consisted of the hcp (A3) form, but contained a minority fcc (A1) phase. Annealing the bilayers at low temperatures (300–450 °C) or for short times resulted in a strengthening of the hcp Co <0001> fiber texture and disappearance of the minor fcc phase. By contrast, annealing at higher temperatures (450–550 °C) or for longer times resulted in the interdiffusion of the Co and CoPt layers and the formation of new Co-Pt solid solutions. One of these solid solutions was found to be hcp in structure, while the other was fcc. The amount of the fcc solid solution increased at the expense of the L10 CoPt, hcp Co and hcp Co-Pt solid solution phases as annealing time and temperature were increased. [Copyright &y& Elsevier]

Abstract: Ternary FeCuPt alloys with 1–5at.% Cu produced no advantage over equivalent binary FePt alloys in terms of lowering the kinetic ordering temperature. The Curie temperature decreased with increasing Cu content. The transformation enthalpy and activation energy were not affected. [Copyright &y& Elsevier]

We outline a computational approach for the study of phase transformations in misfitting thin films and then investigate the kinetics of a transformation to assess the role of heterogeneous nucleation sites, formed in the vicinity of misfit dislocations, in the self-patterning of these systems. Both computer simulation and analytical methods are employed to analyze spatio-temporal correlations in the transforming phase as embodied, in particular, in the transformed volume fraction. To accomplish this, we first obtain an expression for the driving force for nucleation in terms of the strain energy stored in the film under site saturation conditions. This driving force forms the basis for simulations of nucleation and growth in films in which simulation parameters, such as film thickness and temperature, are systematically varied. We find that, in a fully coherent film, there is a retardation of the transformation at certain times that is associated with the constrained film geometry and that, in the presence of misfit dislocations, a range of kinetic behavior can be correlated with the relative magnitude of the driving forces and temperature. The implications of our results for pattern formation in these systems are then discussed. [Copyright &y& Elsevier]

Synthesis of a new tetragonal phase at the equiatomic composition in the archetypal binary Fe-Ni phase diagram is reported. This new phase is proposed as a transitional phase linking cubic FeNi with the chemically ordered tetragonal L1 0 FeNi compound, tetrataenite, of interest as a new advanced permanent magnetic material. This new tetragonal phase was created in a selection of nominally equiatomic FeNi alloys, made either from natural Fe and Ni or from natural Fe combined with the 62 Ni isotope, via application of high-strain processing methods followed by an annealing protocol. High-resolution neutron diffraction affirms that all unprocessed samples adopt the A1-type cubic structure (space group Fm 3 ¯ m ) while all fully processed samples adopt the chemically disordered A6-type tetragonal structure (space group I 4/ mmm ). Magnetic characterization documents a decrease in the initial magnetic susceptibility of deformed samples after annealing, evidencing a processing-induced increase in magnetic anisotropy that may be entirely accounted for by the measured tetragonal distortion. It is proposed that this new phase is a precursor to the formation of tetrataenite (L1 0 FeNi, space group P 4 /mmm ), a meteoritic mineral of high magnetization and appreciable magnetocrystalline anisotropy that requires extraordinarily long cooling periods to form in nature. These results furnish new fundamental information as well as engineering insight for terrestrial synthesis of tetrataenite on industrial timescales, with high relevance for the creation of next-generation permanent magnets comprised entirely of easily accessible, earth-abundant elements. [ABSTRACT FROM AUTHOR]

The thermodynamic and kinetic parameters describing the chemical disordering process of L1 0 FeNi (tetrataenite) are quantified through analysis of calorimetric data obtained from material (Fe 57 Ni 43 ) extracted from the NWA 6259 meteorite. The material presents an endotherm with peak temperatures of 800–860 K depending on heating rate and a transformation enthalpy of 4.0 ± 0.2 kJ/mol of atoms that corresponds to the L1 0 → A1 chemical order–disorder phase transformation. Using reported values of the enthalpy of mixing of the A1 phase and the enthalpy difference between the A1(γ) and the A2(α) phases of Fe, the enthalpy of formation of the L1 0 phase at the composition 43 at.% Ni constituted from Fe and Ni in their standard state is calculated as −4.4 ± 0.6 kJ/mol of atoms. These results indicate that the L1 0 FeNi phase is at the edge of enthalpic stability relative to a mixture of α-Fe and L1 2 FeNi 3 . The measured kinetic chemical-disordering transformation temperature is well above the reported order–disorder temperature of 593 K (320 °C) confirming that the disordering process is highly kinetically limited. The activation energy of chemical disordering of L1 0 FeNi (43 at% Ni) is 3.08 ± 0.07 eV/atom. Results obtained in this study are consistent with a model of one-dimensional growth of the disordered phase wherein the transformation rate is limited by the creation and migration of vacancies. Establishment of the enthalpy difference between the chemically-ordered and -disordered phases as well as determination of the activation energy for transformation provide guidance for laboratory synthesis of the L1 0 FeNi phase, which is of significant applied interest as a new advanced permanent magnet material. [ABSTRACT FROM AUTHOR]

Abstract: A transmission-electron-microscope-based orientation mapping technique that makes use of beam precession to achieve near-kinematical conditions was used to map the phase and crystal orientations in nanolamellar Cu/Nb composites with average layer thicknesses of 86, 30 and 18nm. Maps of high quality and reliability were obtained by comparing the recorded diffraction patterns with pre-calculated templates. Particular care was taken in optimizing the dewarping parameters and in calibrating the frames of reference. Layers with thicknesses as low as 4nm were successfully mapped. Heterophase interface plane and character distributions (HIPD and HICD, respectively) of Cu and Nb phases from the samples were determined from the orientation maps. In addition, local orientation relation stereograms of the Cu/Nb interfaces were calculated, and these revealed the detailed layer-to-layer texture information. The results are in agreement with previously reported neutron-diffraction-based and precession-electron-diffraction-based measurements on an accumulated roll bonding (ARB)-fabricated Cu/Nb sample with an average layer thickness of 30nm as well as scanning-electron-microscope-based electron backscattered diffraction HIPD/HICD plots of ARB-fabricated Cu/Nb samples with layer thicknesses between 200 and 600nm. [Copyright &y& Elsevier]

Abstract: Grain size data were taken from four three- and two-dimensional microstructures, including simulated grain growth, thin film and superalloy data sets. Probability plots revealed approximately log-normal distributions for experimental grain size data sets, but with systematic differences in the upper tails. A simulated grain size data set obtained from Potts model growth exhibited strong deviation from log-normality. A peaks-over-threshold analysis was applied to quantify the differences in the upper tails. Potts model simulation of normal grain growth shows the shortest tail, whereas the thin film data showed the longest tail (i.e. closest to log-normal), with an intermediate tail shape in the superalloy. [Copyright &y& Elsevier]

Precession electron diffraction (PED) is used to acquire orientation information in Cu–Nb nanolamellar composites fabricated by accumulative roll bonding (ARB). The resulting maps quantify the grain size, shape, orientation distributions and interface planes in the vicinity of nanometer-thick deformation twins. The PED-based texture results compare favorably with bulk textures provided by neutron diffraction measurements, indicating uniformity in the ARB Cu–Nb texture. Additionally, {112}Cu||{112}Nb interfaces are present, suggesting that ARB techniques can lead to stable interfaces with a special crystallography. [ABSTRACT FROM AUTHOR]