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A comprehensive investigation of metal–alloy induced crystallization (MAIC) of amorphous silicon (a-Si) is presented. The crystallization processes in three microstructurally principally different, representative types of metal(-alloy)/a-Si systems, Alx(Ge1−x)/a-Si, AgxAl1−x/a-Si, and AlxZn1−x/a-Si, have been monitored by in situ heating x-ray diffraction (XRD) from 25 °C up to 475 °C, until crystallization of a-Si was completed. The obtained experimental results have been systematically compared to predictions obtained by applications of thermodynamic models based on calculations of interface and crystallization energies for the determination of so-called critical thicknesses and initial crystallization temperatures. From the investigation of the MAIC processes in the metal–alloy/a-Si systems, it has been demonstrated that the crystallization temperature and the crystallization kinetics can be well tailored and optimized by controlling the composition and microstructure of the metal alloys. This research, on the one hand, exposes the fundamental, principal role of interface thermodynamics on the crystallization processes and, on the other hand, opens new possibilities for the growth of technologically important, pure, crystalline semiconductor thin films at very low temperatures, as compared to the crystallization temperature of isolated, bulk semiconductor materials. [ABSTRACT FROM AUTHOR]

A model was developed to predict quantitatively the influence of alloying element (Me) dissolved in the ferrite (α) matrix on the incubation time for iron-nitride layer formation upon gaseous nitriding of iron-based alloys. The model incorporates the coupled, concurrent processes of inward diffusion of nitrogen and the depth dependency of the time dependency of the precipitation of alloying-element nitride particles in theαmatrix. Experimental results were obtained by gaseous nitriding of an Fe-2.23 at.% V alloy. The incubation time for iron-nitride formation on Fe–Me alloy is generally much larger than that for iron-nitride formation on pure iron due to a pronouncedly lesser rate of increase of dissolved N content at the surface of Fe–Me alloy. The extent of segregation of N at the MeN/α-Fe interfaces has distinct influence on the incubation time. [ABSTRACT FROM PUBLISHER]

Elastic accommodation of precipitation-induced or thermally induced misfit leads to lattice-parameter changes in crystalline multi-phase systems. Formulae for calculation of such misfit-induced lattice-parameter changes are presented for the aggregate (matrix + second-phase particles) and for the individual matrix and second phase, recognizing the occurrence of either coherent or incoherent diffraction by the matrix and second-phase particles. An overview and an (re)interpretation on the above basis is presented of published lattice-parameter data, obtained by X-ray diffraction analyses of aggregates of matrix plus second-phase particles. Examples for three types of systems consisting of a matrix with misfitting second-phase particles are dealt with, which differ in the origin of the misfit (precipitation or thermally induced) and in the type of diffraction (coherent or incoherent diffraction of matrix plus second-phase particles). The experimental data are shown to be in good to very good agreement with predictions according to the current treatment. [ABSTRACT FROM AUTHOR]

Ambiguity exists in the literature on the crystal structure of Ag3Sn: no agreement on neither the type of orthorhombic distortion nor the presence of ordering exists. Therefore, the exact crystal structure of Ag3Sn has been reinvestigated using high resolution X-ray powder dffraction. By applying Rietveld refinements, it could be shown that Ag3Sn is orthorhombic, with an ordered crystal structure of *#946;-Cu3Ti-type (space group Pmmn). The lattice parameters of a Sn-rich and an Ag-rich sample are a = 4.78233(1) Å, b = 5.99752(1) Å, c = 5.16393(1) Å and a = 4.78291(2) Å, b = 5.98854(2) Å, c = 5.15686(2) Å, respectively. The lattice parameters indicate k-type orthorhombic distortion. [ABSTRACT FROM AUTHOR]

The presence of planar faults complicates the diffraction stress analysis enormously owing to fault-induced displacement, broadening and asymmetry of the Bragg reflections. A dedicated stress-analysis method has been developed for highly planar-faulted, fibre-textured thin films of cubic crystal symmetry, using only specific reflections for diffraction stress analysis. The effect of unjustified use of other reflections has been demonstrated in the course of application of the method to Ni and Ni(W) thin films exhibiting excessive faulting and subjected to (1) a planar, rotationally symmetric stress state and (2) a planar biaxial stress state. In case 1 the crystallite-group method has been used, whereas in case 2 the stress-analysis method based on X-ray stress factors had to be applied. The successful separation of stress- and fault-induced reflection displacements has enabled the investigation of the mechanical behaviour of Ni and Ni(W) thin films by in situ stress measurements during tensile loading, thereby exposing pronounced stiffness and increased strength by alloying with W. [ABSTRACT FROM AUTHOR]

The presence of planar faults complicates the diffraction stress analysis enormously owing to fault-induced displacement, broadening and asymmetry of the Bragg reflections. A dedicated stress-analysis method has been developed for highly planar-faulted, fibre-textured thin films of cubic crystal symmetry, using only specific reflections for diffraction stress analysis. The effect of unjustified use of other reflections has been demonstrated in the course of application of the method to Ni and Ni(W) thin films exhibiting excessive faulting and subjected to (1) a planar, rotationally symmetric stress state and (2) a planar biaxial stress state. In case 1 the crystallite-group method has been used, whereas in case 2 the stress-analysis method based on X-ray stress factors had to be applied. The successful separation of stress- and fault-induced reflection displacements has enabled the investigation of the mechanical behaviour of Ni and Ni(W) thin films by in situ stress measurements during tensile loading, thereby exposing pronounced stiffness and increased strength by alloying with W. [ABSTRACT FROM AUTHOR]

Pure thin tin films, electroplated on copper substrates, were investigated by in situ X-ray diffraction analysis during room-temperature aging, using a laboratory diffractometer equipped with a two-dimensional detector. Diffraction spots of single Sn grains in the Sn film could be observed and traced over time by using the diffraction method adopted. For the as-deposited specimens, striking changes of the Sn reflection spots, concerning their position and intensity, as well as sudden appearances and disappearances of additional diffraction spots, were observed. This could be ascribed to local microstructural changes in the films such as grain rotation, grain growth and grain dissolution. In contrast to the as-deposited specimens, so-called post-baked specimens ( i.e. annealed at 423 K for 1 h after layer deposition) exhibited a stable microstructure. The results obtained are discussed with respect to their relevance for the Sn whisker-growth phenomenon. [ABSTRACT FROM AUTHOR]

The development of uniquely octapod-shaped nanosized amorphous silicon–nitride precipitates in a ferrite matrix was observed upon nitriding of Fe–4.5at.%Si alloy. The legs of the amorphous precipitate are oriented along ⟨1 1 1⟩-directions of the ferrite. The occurrence of such peculiarly shaped amorphous silicon–nitride precipitates, which experience a volume misfit of more than 100% with the surrounding ferrite, was attributed to precipitate growth influenced by long-range diffusion within the evolving highly anisotropic stress field around the developing precipitates after nucleation. [ABSTRACT FROM AUTHOR]

A mixture of pure Ni powder and pure W powder with a nominal composition Ni–15 at.% W was subjected to ball milling in a planetary mill and in a shaker mill. The microstructural evolution upon milling and upon subsequent annealing in the temperature range from 25 to 800 °C was investigated using ex situ and in situ x-ray diffraction integral breadth (single-line and Williamson–Hall) methods and whole powder pattern modeling as well as scanning electron microscopy, transmission electron microscopy, and differential scanning calorimetry. A nanocrystalline Ni(W) solid solution phase develops upon ball milling, with a higher W content by milling in the shaker mill as compared to the planetary mill. Grain coarsening studies indicated a very high stability of the nanocrystalline state, up to almost about 500 °C. Results of annealing at higher temperatures showed that, while the dissolved W content increased in the Ni matrix, a high stability against grain coarsening occurs, which can be ascribed to the presence of (segregated) W atoms at the grain boundaries. [ABSTRACT FROM AUTHOR]

Ni3N was prepared by gaseous nitriding of nickel substrates using gas mixtures of high nitrogen activities, composed of NH3 and H2 at 1 atm and at temperatures between 175 °C and 550 °C. At least above 300 °C closed Ni3N layers developed, which possess distinct compressive macrostrain parallel to the surface. The observed hkl-anisotropy of the macrostrain could be ascribed to the elastic anisotropy as indicated by the single-crystal elastic constants of Ni3N obtained from first-principles calculations performed in this work. The macrostress originates from the thermal misfit between layer and substrate, developing upon cooling. The extent of macrostress is reduced by partial misfit accommodation by plastic deformation as well as by porosity. [ABSTRACT FROM PUBLISHER]

Silicon-nitride precipitation in ferritic Fe–2at.%Si alloy was investigated upon nitriding in NH3/H2 gas mixtures, using light microscopy, hardness measurements, scanning and transmission electron microscopy, X-ray diffraction and electron-probe microanalysis for microstructural characterisation. Surprisingly, ideally weak nitriding behaviour occurred upon nitriding thick (1 mm) recrystallised Fe–2at.%Si alloy specimens. This phenomenon can be attributed to the onset of silicon-nitride precipitation only after a certain degree of nitrogen supersaturation has been established at all depths in the specimen. Silicon-nitride precipitates formed inside the ferrite grains and also along the ferrite grain boundaries. The precipitates were amorphous and had a stoichiometry of Si3N4. The amorphous nature of the tiny precipitates has a thermodynamic origin. Nitride precipitation occurred very slowly due to the very large volume misfit of the nitride with the matrix. An anomalous non-monotonous hardness change occurred with increasing nitriding time, which was ascribed to the initially fully elastic accommodation of precipitate/matrix misfit. The nitrogen uptake rate increased upon continued nitriding as a result of “self-catalysis”. The possible, favourable application of amorphous silicon-nitride precipitates as grain-growth inhibitors in the production of grain-oriented electrical steel is discussed. [ABSTRACT FROM PUBLISHER]

The influence of substitutionally dissolved Al in ferritic Fe–4.75 at.% Al alloy on the nucleation and growth of γ′ iron nitride (Fe4N1− x ) was investigated upon nitriding in NH3/H2 gas mixtures. The nitrided specimens were characterised employing optical microscopy, scanning electron microscopy, transmission electron microscopy, electron probe microanalysis and X-ray diffraction. As compared to the nitriding of pure ferrite (α-Fe), where a layer of γ′ develops at the surface, upon nitriding ferritic Fe–4.75 at.% Al an unusual morphology of γ′ plates develops at the surface, which plates deeply penetrate the substrate. In the diffusion zone, nano-sized precipitates of γ′ and of metastable, cubic (NaCl-type) AlN occur, having, with the ferrite matrix, a Nishiyama–Wassermann orientation relationship and a Bain orientation relationship, respectively. The γ′ plates contain a high density of stacking faults and fine ε iron nitride (Fe2N1− z ) precipitates, although the formation of ε iron nitride is not expected for the employed nitriding parameters. On the basis of dedicated nitriding experiments it is shown that the unusual microstructural development is a consequence of the negligible solubility of Al in γ′ and the obstructed precipitation of the thermodynamically stable, hexagonal (wurtzite-type) AlN in ferrite. [ABSTRACT FROM AUTHOR]

Pure Ni and Ni-W thin films with different W contents (<22 at.%) and a thickness of 500 nm have been produced by (co)sputtering. The phase composition, changes in residual stress, crystallite size, microstrain, and texture have been investigated employing in situ x-ray diffraction measurements (25-550°C) and ex situ transmission electron microscopy analyses. For all compositions investigated, W dissolves substitutionally in Ni. The dissolution of W results in a highly columnar nanocrystalline microstructure with grain aspect ratios (height to width) exceeding 10. The Ni(W) solid solution exhibits a very high density of planar (twin and intrinsic stacking) faults oriented perpendicular to the growth direction. Whereas grain coarsening occurs for the nanocrystalline pure Ni thin films already upon heating to temperatures as low as about 125°C, the microstructure of the nanocrystalline Ni-W thin films remains stable up to much higher temperatures, that is, even exceeding 350°C. Above 350°C, a W depletion of the Ni-W layer as a result of W segregation at planar faults occurs, which is accompanied by a change in lattice constant and in-plane stress. [ABSTRACT FROM AUTHOR]

The time-resolved evolution of intermetallic phase formation in the system pure Sn (polycrystalline coating with a thickness of several microns) on pure Cu (polycrystalline bulk substrate) was investigated in detail by means of focused ion beam and transmission electron microscopy and x-ray diffraction during aging at room temperature for a period of about 1 year. The availability of this coherent data base allowed interpretation of the evolution of intermetallic compound (IMC) formation in terms of interface thermodynamics and interdiffusion kinetics. On this basis spontaneous Sn whiskering on the surface of the Sn coating as a consequence of intermetallic phase (Cu6Sn5) formation along, specifically, Sn grain boundaries intersecting the Sn/Cu interfaces could be discussed. Moreover, a treatment to mitigate spontaneous Sn whiskering on the basis of thermodynamic control of the IMC morphology was proposed. [ABSTRACT FROM AUTHOR]

The allotropic, martensitic phase transformation (hcp → fcc) in cobalt was investigated by differential scanning calorimetry (DSC) upon isochronal annealing at heating rates in the range from 10 K min-1 to 40 K min-1. The microstructural evolution was traced by optical microscopy and X-ray diffractometry. The kinetics of the phase transformation from hcp to fcc Co upon isochronal annealing was described on the basis of a modular phase transformation model. Appropriate model descriptions for athermal nucleation and thermally activated, anisotropic interface controlled growth tailored to the martensitic phase transformation of Co were implemented into the modular model. Fitting of this model of phase transformation kinetics to simultaneously all isochronal DSC runs yielded values for the energy of the interface separating the hcp and fcc Co phase and the activation energy for growth. [ABSTRACT FROM AUTHOR]

The activation energies of heterogeneous equilibrium phase transformations have been frequently determined by Kissinger(-like) analysis. This work demonstrates that the applicability of Kissinger(-like) method(s) to determine activation energies of heterogeneous phase transformations is justified if the phase transformation occurs far away from the equilibrium phase-transformation temperature but not if the phase transformation is investigated in the vicinity of the equilibrium phase-transformation temperature. Experimental results on the kinetics of the order-disorder transformation in NiSn, obtained both near the equilibrium phase-transformation temperature and considerably below it (using quenched samples), expose the non-validity and confirm the validity, respectively, of activation-energy values obtained by Kissinger(-like) analyses applied in the corresponding temperature ranges. Application of the Kissinger(-like) analysis in a temperature range close to the equilibrium phase-transformation temperature leads to erroneous, abnormally high values for the activation energy. [ABSTRACT FROM AUTHOR]

Massive cementite layers with a time-dependent thickness were grown on ferrite substrates by nitrocarburising in a dedicated NH3/H2/CO/N2-containing gas atmosphere at 783 K, 823 K and 843 K. Nitrogen diffusion through the cementite layer into the ferrite substrate took place in conjunction with growth of the cementite layer; a significant, i.e. measurable, solubility of nitrogen in cementite was not observed. The nitrogen concentration-depth profiles in the substrate, underneath the growing cementite layer, were quantitatively determined using a calibrated microhardness measurement technique. The nitrogen concentration-depth profiles were simulated on the basis of a model using an implicit finite-difference method. The simulation yielded values for the diffusivity of nitrogen through cementite, including its activation energy. [ABSTRACT FROM AUTHOR]

A general model to simulate the particle density distribution of a product phase upon phase transformation has been developed in a modular way. In particular, the influence of different nucleation and growth mechanisms known from solid-state phase transformations on the shape of the product phase particle density distribution has been investigated. The model has been fitted to experimental particle density distributions of nanoparticles of fcc Al developing in amorphous Al85Ni8Y5Co2 upon annealing for different times (1 minute to 2 hours) at various temperatures (473 to 508 K). Transient nucleation at a limited number of favored nucleation sites in combination with a two-stage growth mechanism (interface-controlled growth in the beginning and volume diffusion-controlled growth in the subsequent growth stage) very well describes the nanocrystallization process of amorphous Al85Ni8Y5Co2. [ABSTRACT FROM AUTHOR]