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The microstructure and chemical composition of white layers (WLs) formed during hard turning of AISI 52100 steel were studied using atom probe tomography (APT) and transmission electron microscopy (TEM). APT analyses revealed a major difference in the re-distribution of the carbon (C) atoms between WLs formed above and below the A c1 temperature, i.e. T-WL and M-WL, respectively. In T-WL, the C-atoms segregate to grain boundaries (GBs) forming interconnected or isolated C-rich clusters, ∼5 nm, with a concentration of 9.8 ± 0.3 at.%C. Apart from the GB segregation, in M-WLs, large C-rich regions were found with 24.8 ± 0.4 at.%C. Owing to the chemical composition (stoichiometry) and element partitioning of such regions, they were assigned as θ -carbides (cementite). The APT results reveal that the original θ -carbides remain un-dissolved in the M-WLs, but might be plastically deformed due to the excessive strain that exists in hard machining process. The obtained results are in good agreement with the temperatures that are reached during formation of M-WLs. The isolated nano-sized C-clusters were assigned as off-stoichiometric carbides whereas the interconnected C-rich clusters were attributed to Cottrell atmospheres, evident by the linear shape of the C-enrichment as observed in the APT reconstructions. The C-contents in the nano-sized martensitic and ferritic grains were estimated to 0.50 ± 0.06 at.%C and ∼0.46 ± 0.02 at.%C, respectively. The C-content in the ferritic grains, beyond the C-solubility limit in ferrite (<0.1 at.%) is governed by the high dislocation density inside the grains, supported by the favorable binding energy between dislocations and C-atoms compared to C-atoms and Fe in carbides. No other evidence of redistribution of the substitutional alloying elements was observed. TEM analyses showed that T-WLs comprises of an equiaxed and nano-sized grains with well-defined cell boundaries, whereas the structure in the M-WLs comprised of elongated sub-grains formed via re-orientation of the original martensite followed by breakage/partitioning into elongated sub-grains. [ABSTRACT FROM AUTHOR]

We have investigated the physical origin of anomalous in-plane thermal expansion (TE) anisotropy leading to invar-like behavior and negative TE in nanostructured NiTi sheets manufactured via severe cold-rolling. The roles of grain size (GS), crystallographic texture, thermally-induced phase transformation, and intrinsic (lattice level) TE of austenite (B2) and martensite (B19′) phases on the macroscopic TE behavior are addressed. It is shown that by controlling the cold-rolling thickness reduction and heat-treatment temperature the coefficient of thermal expansion (CTE) can be controlled in a wide range from positive ( α ∼ 2.1 × 10 −5 K −1 ) to negative ( α ∼ −1.1 × 10 −5 K −1 ) via in-plane anisotropy of TE. A very small CTE of α ∼ −5.3 × 10 −7 K −1 (invar-like behavior) in a wide temperature window of 230 K (353–123 K) is obtained at an angle of 33.5° to the rolling direction (RD) of the severely cold-rolled sheet. TEM and XRD studies show that the microstructure underlying such anomalous TE behavior consists of a mixture of B2 nano-grains and retained/residual deformation-induced martensite and that the observed anomalous TE anisotropy is due to the intrinsic anisotropic TE of residual martensite. The invar-like behavior is the result of the cancellation of the positive TE of austenite phase with the negative TE of residual martensite along 33.5° to the RD. A simple rule of mixture model incorporating the intrinsic TE of B2 and B19′ lattices and the texture coefficients of the sample is proposed which successfully captures the anomalous in-plane TE anisotropy. The discovery of high dimensional stability over a wide temperature window along with temperature insensitive non-hysteretic linear superelasticity of the severely-deformed NiTi opens up a new route for designing stable SMAs for applications in ragged environments. [ABSTRACT FROM AUTHOR]

Abstract: Rapid annealing (4–10s) induced primary crystallization of soft magnetic Fe–Si nanocrystals in a Fe73.5Si15.5Cu1Nb3B7 amorphous alloy has been systematically studied by atom probe tomography in comparison with conventional annealing (30–60min). It was found that the nanostructure obtained after rapid annealing is basically the same, irrespective of the different time scales of annealing. This underlines the crucial role of Cu during structure formation. Accordingly, the clustering of Cu atoms starts at least 50°C below the onset temperature of primary crystallization. As a consequence, coarsening of Cu atomic clusters also starts prior to crystallization, resulting in a reduction of available nucleation sites during Fe–Si nanocrystallization. Furthermore, the experimental results explicitly show that these Cu clusters initially induce a local enrichment of Fe and Si in the amorphous matrix. These local chemical heterogeneities are proposed to be the actual nuclei for subsequent nanocrystallization. Nevertheless, rapid annealing in comparison with conventional annealing results in the formation of ∼30% smaller Fe–Si nanocrystals, but of identical structure, volume fraction and chemical composition, indicating the limited influence of thermal treatment on nanocrystallization, owing to the effect of Cu. [Copyright &y& Elsevier]

Abstract: This work quantifies the effect of grain size on grain boundary diffusivity. Diffusion of Au into Cu thin films of varying grain size is measured using secondary ion mass spectroscopy depth profiles. Appropriate models for fitting the composition profiles to analytical solutions to diffusion equations are identified by characterizing the microstructure both before and after the diffusion anneal. Finite-element numerical simulations are also employed to extract the diffusion coefficients directly from fits to experimental data. The results indicate that factors such as non-columnar grains, migrating grain boundaries, dislocations and stress gradients must be appropriately accounted for in order to obtain meaningful results. Overall, a strong scaling effect is not observed, which suggests that the atomic structure of boundaries in nanocrystalline thin-film materials probably resembles that of their coarse-grained counterparts. [Copyright &y& Elsevier]

Abstract: One of the toughest challenges that hinders the application of ceramic coatings is their poor damage tolerance. Addressing this problem requires the development of novel micro- or nanostructures that would impart to these coatings both high hardness and high toughness. In this paper, CrAlN coatings, with varying Al contents up to 30at.%, were engineered onto steel substrates using the magnetron sputtering technique. Whilst the addition of Al does not significantly alter the columnar microstructure, it does change the preferred grain orientation and increase the compressive residual stress. Moreover, the hardness, elastic strain to failure (H/E) and plastic deformation resistance (H 3/E 2) of the resultant CrAlN coating with the highest Al content were found to increase ∼47, ∼29 and ∼140%, respectively, as compared to CrN. Evidence collected from transmission electron microscopy and X-ray photoelectron spectroscopy experiments shows that AlN, existing in an amorphous state at the columnar CrN grain boundaries, has a crucial role in providing the unusual combination of high hardness and exceptional damage resistance. The results provide a new pathway to developing durable ceramic coatings suitable for applications involving severe loading conditions. [Copyright &y& Elsevier]

Abstract: We study two-dimensional grain growth at the nanoscale using the phase field crystal (PFC) model. Our results show that for circular grains with large misorientations the grain area decreases linearly with time, in good agreement with classical grain growth theory. For circular grains with small initial misorientations, grain rotation occurs as a result of the coupled motion between the normal motion of the grain boundary and the tangential motion of the adjacent grains. Despite this rotation and its effect on the grain boundary energy, the grain area decreases linearly with time. In addition, for intermediate initial grain misorientations, we find a repeating faceting–defaceting transition during grain shrinkage and a different relationship between the grain area and time, which suggests a different grain growth mechanism than that for small and large misorientations. For a circular grain embedded between a bicrystal with a symmetric tilt boundary, we find that the evolution of the embedded grain closely depends on dislocation reactions at triple junctions. [Copyright &y& Elsevier]

Abstract: Thin film components of conventional and flexible solid-state devices experience mechanical strain during fabrication and operation. At the bulk scale, small values of strain do not affect thermal conductivity, but this may not true for grain sizes comparable with the electron and phonon mean free paths and for higher volume fraction of grain boundaries. To investigate this hypothesis, thermal and electrical conductivity of nominally 125-nm-thick aluminum films (average grain size 50nm) were measured as functions of tensile thermo-mechanical strain, using a modified version of the 3-ω technique. Experimental results show pronounced strain–thermal conductivity coupling, with ∼50% reduction in thermal conductivity at ∼0.25% strain. The analysis shows that mechanical strain decreases the mean free path of the thermal conduction electrons, primarily through enhanced scattering at the moving grain boundaries. This conclusion is supported by similar effects of mechanical loading observed on the electrical conduction in the nanoscale aluminum specimens. [ABSTRACT FROM AUTHOR]

Abstract: Both pulsed-DC biased and commercial ion-beam sputtered VO x thin films maintain a face-centered-cubic nanocrystalline phase, even for stoichiometries of x >1.5, which is well outside the bulk equilibrium solubility range for cubic VO x . Many of these highly nonstoichiometric films exhibit a high density of microtwins, which give rise to unusual fine structure in the selected-area electron diffraction patterns, namely: an additional defect ring; a significant broadening of the {200} ring; pairs of parallel rod features which are tangent to the additional defect ring; and additional fine-structure features between the {200} and {220} rings. The formation of the microtwins is correlated with the coalescence of vanadium vacancies along the {111} twin planes in the crystalline lattice. [Copyright &y& Elsevier]

Abstract: Transmission electron microscopy, electrical resistivity measurements and mechanical testing were employed to investigate the evolution of microstructure and functional superelastic properties of 0.1mm diameter as-drawn Ni–Ti wires subjected to a non-conventional heat treatment by controlled electric pulse currents. This method enables a better control of the recovery and recrystallization processes taking place during the heat treatment and accordingly a better control on the final microstructure. Using a stepwise approach of millisecond pulse annealing, it is shown how the microstructure evolves from a severely deformed state with no functional properties to an optimal nanograined microstructure (20–50nm) that is partially recovered through polygonization and partially recrystallized and that has the best functional properties. Such a microstructure is highly resistant against dislocation slip upon cycling, while microstructures annealed for longer times and showing mostly recrystallized grains were prone to dislocation slip, particularly as the grain size exceeds 200nm. [Copyright &y& Elsevier]

Abstract: Blends consisting of doped silicon nanocrystals (Si-ncs) and two conjugated polymers (poly(3-hexylthiophene) (P3HT) and poly(methoxy ethylexyloxy phenylenevinilene) (MEH PPV)) with improved photostability were fabricated. We show that a top-down approach by electrochemical etching is suitable for preparing doped (boron and phosphorus) freestanding and surfactant-free Si-ncs. The doping of Si-ncs was confirmed by low temperature photoluminescence and electron spin resonance analysis. It is demonstrated that such Si-ncs can be successfully used for the fabrication of room temperature photoluminescent and photosensitive blends. We argue that the luminescence and transport properties of the blends are controlled by the Si-ncs properties and could be assigned to quantum confinement of excitons in nanocrystalites with an energy band gap of ∼2eV. Furthermore, the blending of doped Si-ncs in both conjugated polymers led to the establishment of a bulk heterojunction between the Si-ncs and polymer. The difference in electron affinity and ionization potential between nanocrystals and polymer dissociated the excitons. Those blends showed increased carrier transport and photoconductivity under ambient conditions. It was found that introduction of less defective p-type doped Si-ncs significantly improved overall photostability of the blend. The Si-ncs non-toxicity and easy integration into well-established silicon technologies might bring considerable benefit for hybrid optoelectronic and photovoltaic device development. [Copyright &y& Elsevier]

Abstract: The microstructural evolution of Cr–Si–N films deposited by a hybrid arc ion plating and magnetron sputtering process was investigated by varying the sputtering power of Si target and substrate bias voltage. Detailed nanocomposite microstructures of the films were studied by high-resolution transmission electron microscopy. The results indicated that the incorporation of Si into the growing CrN films at 0V led to the formation of a nanocomposite containing CrN nanocolumns embedded in amorphous SiN x matrix or near-amorphous microstructure. For the films having a Si content of ∼10at.% and ∼15at.%, a negative bias voltage of −50V resulted in the aggregation of nanocolumns in the amorphous matrix. Further increase of negative bias voltage to −250V led to the formation of a three-dimensional CrN/a-SiN x nanocomposite microstructure. The mechanism of microstructure evolution is discussed by considering the thermodynamic and kinetic factors. [Copyright &y& Elsevier]

Abstract: We report on the synthesis of some novel organic–inorganic hybrid 2D perovskite semiconductors (R-(CH2) n NH3)2PbX4. These semiconductors are self-assembled intercalation nanolayers and have a multi-quantum-well energy level structure. We systematically vary the characteristic of organic groups (R-(CH2) n ) to study the relationship between their structures and the optical properties of (R-(CH2) n NH3)2PbX4. From optical absorption and photoluminescence spectroscopy experiments performed on series of samples, we find some trends of choosing the organic groups to improve the optical performance of (R-(CH2) n NH3)2PbX4. A new organic group, which allows synthesis of nanolayer perovskite semiconductors with quite high photoluminescence efficiency and better long-term stability, has been found. [Copyright &y& Elsevier]

Abstract: Materials synthesized by deposition techniques are often plagued by high levels of residual stress. While the origin and control of this stress in thin (sub-micron) films has been an active area of research, it is not clear how the results extrapolate with thickness. In the present work, in situ residual stress measurements are performed during the sputter deposition of beryllium, spanning the transition from thin to thick. Variables including sputtering gas pressure and substrate biasing are shown to strongly affect both the average and instantaneous stress levels measured during film growth. Detailed microstructural characterization is performed to assess the grain structure, surface morphology, and crystallographic growth texture of representative specimens. The microstructure is correlated with theoretical models of stress generation to interpret experimental measurements. A stress map is also constructed, generalizing the effects of processing and material parameters on stress state. [Copyright &y& Elsevier]

Abstract: The realtime evolution of stress during metal-induced crystallization (MIC) in amorphous Ge/crystalline Al bilayers was explored by an in situ X-ray diffraction technique in the temperature range of room temperature to 250°C. The realtime stress developments, in combination with ex situ microstructural and thermal characterizations, revealed complex, distinct correlations of, on the one hand, stress generation and stress relaxation, and, on the other hand, microstructural evolution during the MIC process. MIC in this system is revealed to proceed by rapid crystallization of amorphous Ge at 150°C and subsequent growth of the crystallized Ge nano-grains at temperatures between 150°C and 250°C, in association with a gradual exchange of the positions of the Al and crystallized Ge sublayers. The development of the microstructure and the state of residual stress was interpreted in terms of acting driving forces and operating mechanisms. [Copyright &y& Elsevier]

Abstract: Theoretical models are suggested that describe the effects of stress-driven migration of grain boundaries (GBs) on both the formation of nanoscale cracks (nanocracks) and the growth of comparatively large cracks in deformed nanocrystalline ceramics and metals. The GB migration under consideration is driven by the applied stress, carries plastic flow and produces quadrupoles of disclination defects in nanocrystalline materials. The disclinations create high local stresses capable of initiating the formation of nanocracks. In this paper, the conditions at which the formation of nanocracks is energetically favorable are theoretically described. The external stress values needed to initiate nanocrack formation near the disclinations in nanocrystalline metals (Al and Ni) with the finest grains and nanoceramics are estimated. In addition, we estimated the effect of the stress-driven migration of GBs on the growth of pre-existing, comparatively large cracks in nanocrystalline Ni with the finest grains. [Copyright &y& Elsevier]

Abstract: On a thermodynamic foundation, in particular for interface energetics, the initial oxide overgrowth on a bare metal surface can be predicted to be either amorphous or (semi-)coherent crystalline, as function of the oxidation temperature and substrate orientation. Model calculations were performed for a range of metal/oxide systems (oxidation of Al, Ni, Cu, Cr, Fe, Mg, Zr and Ti) on the basis of the sum of the surface, interfacial and bulk energy differences between the competing amorphous and crystalline oxide overgrowths on the same metal substrate. It follows that an amorphous state for the initial oxide overgrowth can be thermodynamically (instead of kinetically) preferred as long as the higher bulk Gibbs energy of the amorphous oxide overgrowth is overcompensated for by its low sum of surface and interface energies. The dominating factors, which thermodynamically favour the formation of an amorphous oxide overgrowth, are exposed and discussed. [Copyright &y& Elsevier]

Abstract: Tungsten oxide (WO3) thin film mesophases encompassing a well-organized network of grains with a triclinic phase and pores with diameters in the range of 2–5nm were generated at room temperature by template-assisted electrodeposition involving a novel combination of ionic and polymeric surfactants. Electron microscopy studies revealed the surface texture of the films annealed at 250 and 500°C to be primarily composed of randomly oriented rod and sheet-like shapes and the bulk structure of these films to ensconce fibril-like shapes and distinct spherical nanoparticles, along with elongated pores. Coloration efficiency, transmission modulation and charge density for lithium insertion are greater, switching rates are faster (colors in 8.8s and bleaches in 1.5s for a 50% transmittance change) and cycling stability is superior for the as-deposited film as compared with the annealed WO3 films. The superior electrochromic performance characteristics of the as-deposited WO3 coatings are a direct manifestation of the mesoporosity over multiple length scales, a good lateral organization of grains and pores which facilitate ion insertion and extraction, and a large number of accessible surface sites which ensure a high proportion of W5+ color centers in the film upon lithium intercalation. In spite of the retention of a porous structure by the film annealed at 500°C, the poor electrochromic response of the annealed films is attributed to the coarse grain rod-, sheet- and fiber-like framework, which efficiently obstructs lithium ion movement and uptake. [Copyright &y& Elsevier]

Abstract: Fe91– x Mo8Cu1B x (x =12, 15, 17, 20) amorphous and nanocrystalline alloys were studied to examine the influence of B content on their microstructure and magnetic behaviour. Changes in the magnetic properties provoked by microstructural evolution upon thermal treatments of as-cast samples were also analyzed. Nanocrystallization kinetics can be described by an isokinetic approach except for the 20at.% B content alloy. The Curie temperature of the amorphous as-cast samples increases with the alloy’s B content. Mössbauer results suggest the presence of Mo atoms in the nanocrystals. Crystalline volume fraction and mean grain size of the nanocrystals at the end of the nanocrystallization process are higher for the lowest B content alloy. The 20at.% B content alloy develops a boride phase just after the early stages of the nanocrystallization process, which provokes a magnetic hardening in this alloy. The softest magnetic behaviour of the studied compositions corresponds to nanocrystallized 17at.% B content alloy. [Copyright &y& Elsevier]

Abstract: Using the unique capabilities and high time resolution of dynamic transmission electron microscopy (DTEM), the fast kinetics of α→β-phase transformation in nanocrystalline Ti films were investigated using single-shot electron diffraction and bright-field TEM images. From quantitative analysis of the diffraction patterns, the transformation rates were determined for temperatures between transition start (1155K) and melt temperature (1943K). The experimental data were summarized in a time–temperature-transformation (TTT) curve with nanosecond time resolution. Theoretical TTT curves were calculated using analytical models for isothermal martensite and available thermodynamic data. Above 1300K, there is excellent agreement between the experiment and the discrete–obstacle interaction model, suggesting that the nucleation rate and thermally assisted motion of the martensite interface are controlled by interface–solute atom interactions. However, theory predicts much slower transformation rates near the transition temperature than experiment. Experimental data fits using the Pati–Cohen model suggests that an increase in autocatalytic nucleation may partially account for the fast transformation rates at lower temperatures. [Copyright &y& Elsevier]

Abstract: Nanocomposite CrAlSiN compounds prepared by the cathodic arc evaporation technique were subjected to structural and mechanical characterization tests. X-ray diffraction, X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM) were employed to investigate the effects of Si addition on the structure and phase development of the metastable NaCl structure of high aluminum CrAlN films. TEM studies revealed that partial substitution of the metal component by Si in CrAlN results in the nucleation of a wurtzite h-AlN phase even for amounts of silicon as low as ∼2–3at.%. XAS measurements at the Cr and Si K-edges indicated that the local environment of Cr atoms is strongly affected by the Si addition, and that silicon may also be part of the crystalline phase. These results indicate the formation of complex Cr–Si–X compounds, where X can be N, Al or both, and the formation of composite nanocrystalline CrAlSiN films. [Copyright &y& Elsevier]

Abstract: An approach based on the grain coalescence mechanism is developed to explain and predict the elastic behavior (and stress) of nanocrystalline films. The model explains how, under an external strain, coalescence and decoalescence at grain boundaries alter the stress state of the film, thereby reducing the film’s effective Young’s modulus. An assessment of the effect of coalescence at grain boundaries could be made on the basis of the analysis of the contributions of grain boundary and strain energies. The estimations of Young’s modulus and stress based on the model are in agreement with the data experimentally observed for sputtered iron nanocrystalline films. [Copyright &y& Elsevier]

Abstract: Nanostructured tungsten oxide (WO3) thin films have been electrochemically grown from a self-assembly of sodium dodecyl sulfate–tungsten oxide aggregates at the electrode–electrolyte interface. The nanoparticulates embedded in a quasi-layered structure of the as-deposited WO3 film with a single-crystalline hexagonal phase transform to a hybrid microstructure encapsulating both nanoscaled particles and rods with a tetragonal modification at 100°C, reverting again to orthorhombic single-crystalline nanoplatelets and bunches of tangled nanowires at 250°C and finally coarse nanoparticles at 500°C. The WO3 film annealed at 100°C shows the fastest color-bleach kinetics, highest optical modulation and coloration efficiency, which is a repercussion of the pentagonal channels equipped with the tetragonal phase, the mesopore structure and the channeled porosity. In spite of perpendicularly oriented hexagonal channels, which facilitate ion insertion, the switching performance of the as-deposited films comes a close second owing to extremely random pore morphology. Poor color-bleach rates observed for the films annealed at 250 and 500°C are attributed to pore shrinkage, high density and crystallinity. [Copyright &y& Elsevier]

Abstract: High-resolution transmission electron microscopy and three-dimensional atom probe observations show clearly that a reverse transformation of body-centred cubic ferrite to face-centred cubic austenite occurs during severe plastic deformation of a pearlitic steel resulting in a nanocrystalline structure, something that never occurs in conventional deformation of coarse-grained iron and steels. The driving force and the mechanisms of this reverse transformation are discussed. It is shown that nanostructure and shear stresses are essential for this process, and the results confirm molecular dynamics predictions of such transformations in nanocrystalline iron. [Copyright &y& Elsevier]

Abstract: The superplastic deformation of nano-sized (∼68nm) Si3N4 ceramics has been studied in compression over a wide range of strain rates and temperatures. The experimental results revealed, for the first time, a transition in the stress exponent (n) at each temperature. The n values decreased from ∼2 to ∼1 with increasing stress. The activation energy was also different for the two regions, decreasing from 858.2kJ/mol in the n ∼2 region to 571.8kJ/mol in the n ∼1 region. Concurrent grain growth occurred during deformation tests; however, grain growth was not accompanied by obvious strain hardening due to the strong texture developed. Assessment of possible rate controlling deformation mechanism indicated that in the n ∼2 region, superplastic behavior was considered to be controlled by the interface-reaction controlled solution-precipitation process with two-dimensional nucleation, whereas deformation in the n ∼1 region was controlled by a grain boundary sliding process accommodated by a diffusion-controlled solution-precipitation. [Copyright &y& Elsevier]

Abstract: A new approach is proposed for the study of crystallization processes under the hypothesis of isokinetic behavior. From a direct extension of the Avrami theory to non-isothermal regimes, an expression of the local Avrami exponent as a function of the crystalline volume fraction is obtained from a single DSC run performed at a constant heating rate and a raw estimation of the activation energy (a variation of the activation energy value between 3 and 5 eV produces a change on the Avrami exponent smaller than ±0.1). This approximation was applied to the nanocrystallization process of a FeCoNbB(Cu) alloy series and the results found are in good agreement with previous isothermal analysis on the same alloys. The kinetics is characterized by an initial Avrami exponent close to unity, which decreases down to values below 0.5 as the crystalline volume fraction increases. [Copyright &y& Elsevier]

Abstract: The martensitic phase transformation of nanocrystalline NiTi causes a unique “herring-bone” microstructure of B19′ not encountered in the coarse grains. The constraints of the grain boundaries make a nanoscale compensation of the transformation strains necessary that is obtained by the autocatalytic formation of self-accommodated lamellae containing (001)m compound twins. The coherent junction planes of the twinned lamellae were analysed by high-resolution transmission electron microscopy. Alternating segments of the interface are composed of lattice planes of matching nanotwins that are structurally very similar and almost parallel. The compensation of transformation deformations is facilitated by invariant interfaces yielding energy minimization and strain compatibility. Using the geometrically nonlinear theory of the martensitic transformation, a systematic classification of the interfaces is proposed that is based on crystalline symmetry and predicts the observed geometry of both straight and curved junction planes of the “herring-bone” microstructure. [Copyright &y& Elsevier]

Abstract: A filamentary composite elaborated by cold drawing was processed by high pressure and torsion (HPT). The nanostructure resulting from this severe plastic deformation (SPD) was investigated thanks to scanning electron microscopy, transmission electron microscopy, X-ray diffraction and 3D atom probe. Although the mutual solubility of Cu and Fe is extremely low at room temperature in equilibrium conditions, it is shown that nanoscaled Fe clusters dissolve in the Cu matrix. The non-equilibrium copper supersaturated solid solutions contain up to 20at.% Fe. The driving force of the dissolution is attributed to capillary pressures and mechanisms which could enhance the atomic mobility during HPT are discussed. We conclude that the interdiffusion is the result of a dramatic increase of the vacancy concentration during SPD. [Copyright &y& Elsevier]

Abstract: The partial substitutions of Co for Fe and Ge for B are studied for a Fe83−xCoxZr6B10−yGeyCu1 alloy series (x=0, 5 and 20; y=0 and 5) as a possible way of enhancing the high temperature applicability of NANOPERM alloys. The devitrification process, the nanocrystallization kinetics and the nanocrystalline microstructure are similar for all the studied alloys. Good soft magnetic properties are observed even at a high crystalline volume fraction of body-centered cubic α-Fe nanocrystals, which are stable up to ∼1000 K. The partial substitution of Co for Fe is very effective to increase the Curie temperature of the residual amorphous matrix . Although the substitution of Ge for B is ineffective to increase , a clear increase of the saturation magnetization with respect to the Ge-free alloy can be observed. [Copyright &y& Elsevier]

Abstract: From the quaternary Ti–Zr–Hf–Ni phase diagram, the cross-section at 20 at.% Ni was selected for investigation. The icosahedral quasicrystalline, crystalline and amorphous phases were observed to form in nine kinds of rapidly solidified (TixZryHfz)80Ni20 (x+y+z=1) alloys at different compositions. The quasilattice constants of 0.519 and 0.531 nm were obtained for the icosahedral phase formed in the melt-spun Ti40Zr20Hf20Ni20 and Ti20Zr40Hf20Ni20 alloys, respectively. The icosahedral phase formed in the melt-spun Ti40Zr20Hf20Ni20 alloy especially is thermodynamically stable. The supercooled liquid region of the Ti20Zr20Hf40Ni20 glassy alloy reached 64 K. From these results a comparison of quasicrystal-forming and glass-forming abilities was carried out. The quasicrystal-forming ability was reduced and glass-forming ability was improved with an increase in Hf and Zr contents in the (TixZryHfz)80Ni20 alloys. On the other hand, an increase in Ti content caused an improvement in quasicrystal-forming ability. [Copyright &y& Elsevier]

Molecular dynamics (MD) simulations, employing semi-empirical glue-type (similar to embedded atom method) many-body potentials, have been used to model the melting behavior of nanosized Pb particles embedded in an Al matrix. All the Pb particles studied melt well above the bulk melting temperature, with the melting point elevation displaying a damped periodic trend with increasing Pb particle size. By inspecting snapshots derived from the simulations, it is also possible to conclude that melting occurs via nucleation at {1 0 0} interfaces. A phenomenological model, based on the consideration of interfacial energy, volume expansion and lattice mismatch, has been developed to describe this interesting melting behavior. Our model leads to the conclusion that the periodic variation of melting point with size is due to an oscillatory strain energy contribution arising from the large size mismatch of Pb and Al atoms. [Copyright &y& Elsevier]

In the previous papers, we reported the synthesis of nickel nanocrystals encapsulated in an amorphous carbon matrix by a method that consists in the sonochemical decomposition of the Ni(COD)2 organometalic precursor followed by a heating treatment in vacuum. Both as-prepared and heated samples have been further characterised in the present paper by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) to determine the microstructure and the stability of the nickel nanocrystals for long periods of air storage. It has been shown that carbon is protecting the nickel nanocrystals from oxidation leading to a magnetic behaviour of the sample congruent with the superparamagnetic properties of single domain particles. The analysis of the frequency-dependent ac susceptibility leads to two well-defined distributions of particle size consistent with those observed in TEM experiments. The effective anisotropy constant has been determined for the two particle sizes of nickel nanoparticles. [Copyright &y& Elsevier]

Using both conventional and high-resolution transmission electron microscopy (HRTEM), the effect of bending at room temperature on the microstructure of amorphous Al90Fe5Gd5 was investigated. In the compressive region, nanocrystallites formed at shear bands, along small cracks and at the fracture surface; in the tensile region, nanocrystallites were observed only at the fracture surface. Combining HRTEM with frequency filtering, low-density, nanoscale defects at shear bands were imaged. In the compressive region, both the shear bands and the undeformed matrix contain few defects. In the tensile region, there is a uniform distribution of defects within the shear bands. The preferential precipitation of nanocrystallites in the compressive region is attributed to a kinetic effect due to the uniformly distributed free volume in the shear bands. In contrast, the formation of the nanocrystallites at the fracture surfaces is likely due to adiabatic heating induced by fracture. [Copyright &y& Elsevier]