Positron annihilation study of ageing precipitation in deformed Fe–Cu–B–N–C

The role of deformation-induced defects and carbon addition on copper precipitation during ageing at 550?°C is investigated in high-purity Fe–Cu–B–N–C alloy samples by positron annihilation spectroscopy. Complementary small-angle neutron scattering (SANS) and hardness tests are utilized to characterize the size distribution of the Cu precipitates formed and their influence on the mechanical properties. Samples with 0 and 8% cold pre-strain are utilized to study the influence of prior tensile deformation on the precipitation kinetics of copper. The time evolution of the coincidence Doppler-broadening spectra indicates that deformation-induced defects enhance the Cu precipitation kinetics, which is confirmed by the SANS results. In the S–W plot, a clear reduction in open volume defects is accompanied by a strong increase of Cu signature during the initial stage of ageing, implying that the open volume defects (mainly dislocations) act as nucleation sites for Cu precipitation. A comparison between the precipitation behaviour of Fe–Cu, Fe–Cu–B–N and Fe–Cu–B–N–C indicates that the addition of carbon does not alter the Cu precipitation mechanism but decelerates the kinetics. Hardness results confirm that carbon counteracts the acceleration of Cu precipitation caused by the addition of B and N.     

The heat treatment response of semisolid formed Al–5Fe–4Cu alloy

The effect of heat treatment on both microstructures and performances of semisolid Al–5Fe–4Cu alloy was investigated with scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) and tensile test. The results showed that the semi-solid Al–5Fe–4Cu alloy’s response to the solution heat treatment (SHT) is abnormal compared with the conventional semi-solid Al alloys, i.e. the tensile properties of the semi-solid Al–5Fe–4Cu alloy decreased significantly after SHT. Nevertheless, the semi-solid Al–5Fe–4Cu alloy subject to direct ageing without SHT could exhibit conspicuous improvement of the tensile properties. And, the reason of the abnormal results has been analysed and discussed in detail.     

Diffusion paths in single-phase ternary metal systems

An analysis of diffusion paths in single-phase ternary metal systems Co–Fe–Ni and Cu–Fe–Ni on the basis of the phenomenological interdiffusion model using effective interdiffusion coefficients is presented. The peculiarities of practical application of effective interdiffusion coefficients of components for calculating diffusion paths in ternary systems are analysed. It is done on the basis of the relationship between effective interdiffusion coefficients and the diffusion paths. The results were found to be in good agreement with experimental data for the ternary systems Co–Ni–Fe and Cu–Ni–Fe. It is shown that deviation of the diffusion path from linearity in ternary single-phase diffusion couple in the system Cu–Ni–Fe mainly depends on the thermodynamic properties of the system.     

Influence of the thermal power of a Fe atomic flux on the formation of Cu/Fe nanofilms on a Si(001) substrate

The growth of a Fe sublayer 1.5–14.0 monolayers (MLs) thick and a Cu film (about 5 MLs) on this sublayer is studied at a reduced temperature (1240°C) and an elevated temperature (1400°C) of a Fe source and at a reduced temperature (900°C) of a Cu source. The films are examined by Auger electron spectroscopy, low-energy electron diffraction, and atomic force microscopy. As metal sources, thin Fe and Cu strips on a Ta foil are used. It is shown that a nonequilibrium 2D phase forms in the Fe-on-Si(001) film up to a thickness of 4–5 MLs. This phase appears as closely packed atomically smooth nanoislands. When the thickness of the film exceeds 4–5 MLs, the nonequilibrium Fe phase changes to the bulk (3D) phase of Fe and its silicide Fe _x Si. At Fe source temperatures of 1240 and 1400°C, the nonequilibrium phase consists of Fe with Si segregated on the Fe surface, and a Fe-Si mixture. Copper on the nonequilibrium Fe and Fe-Si phases grows, respectively, as a smooth layer Cu with Si segregated on the top and in the form of Cu-Fe and Cu-Si mixtures. Cu islands growing on the bulk Fe and Fe _x Si phases have smaller and larger sizes, respectively.     

Monte Carlo simulations of copper clustering in Fe–Cu alloys under irradiation

We present the computational approach for studying the microstructures of Cu clusters in Fe–Cu alloys by combining the molecular dynamics (MD) simulation and Monte Carlo methods. The MD simulation is used to characterize the primary damage resulting from the displacement cascade in Fe. Then, using the Metropolis Monte Carlo methods, the microstructure of the Cu clusters is predicted under the assumption that the system will evolve towards the equilibrium state. The formation of the Cu clusters is apparent for Fe–Cu alloys of a higher Cu content (1.0 w/o), whereas the degree of Cu clustering is not significant for the lower Cu content (0.1 w/o) alloys. The atomic configuration of the Cu–vacancy complex under irradiation, produced by this simulation, is in a fair agreement with the experiments. The simulation is expected to provide important information on the Cu-cluster morphology, which is useful for experimental data analysis.     

Mössbauer study of magnetic ordering and superconductivity in YBa2(Cu1−xFex)3O7

We have made superconducting samples of the Y?Ba?Cu?O system with Fe substituted for the Cu. The percentage of Fe substituted varied from 2 to 100. The samples have been verified by x-ray diffraction to be single-phase 1–2–3 compounds. The 6% Fe substitution reduces T_c from 94 K to 80 K. The room temperature Mössbauer spectrum shows two pairs of doublets, indicating there are two distinct Cu sites in the sample. The most surprising result is that magnetic ordering of the Fe coexists with superconductivity of the material at 4.2 K.     

Effects of damage rate on Cu precipitation in Fe–Cu model alloys under neutron irradiation

The formation of Cu precipitates and point defect clusters was investigated in two Fe–Cu binary model alloys, Fe–0.3Cu and Fe–0.6Cu, irradiated at 573?K at three different damage rates, namely 3.8?×?10^?10, 1.5?×?10^?8 and 5?×?10^?8?dpa (displacements per atom)/s, up to about 1.6?×?10^?2?dpa. Results of positron annihilation experiments indicated that Cu precipitates were formed in these irradiations with different damage rates. The growth of Cu precipitates does not increase monotonously with increasing irradiation dose, but it rather depends on the nucleation and growth of microvoids. It is also clear that the nucleation and growth of microvoids are influenced by the irradiation dose rate.     

Magnetic and electronic properties of Fe/Cu multilayered nanowires: A first-principles investigation

By using the first-principles calculations, we have systematically investigated the equilibrium structure, magnetic and electronic properties of one-dimensional Fe/Cu multilayered nanowires. We find that the stability of the Fe/Cu multilayered nanowires decreases with increasing concentration of nonmagnetic Cu layers, suggesting that rich Fe nanowires are more stable. Analysis of the average magnetic moment (μ_av) per Fe atom in the Fe/Cu multilayered nanowire suggests that there is a slight increase in μ_av with the increase in the number of nonmagnetic Cu layers, which was attributed to the increased Fe–Cu distance with increase in the Cu layers at interfacial layers. Furthermore, analysis of the band structures of these nanowires suggests strong dependence of conductance on the nonmagnetic Cu spacer layer thickness and a half-metallic character is observed for moderate Cu atoms substitutions, opening up the possibility for their application in magnetoelectronics or spintronics.     

Hydrothermal conversion of graphite to carbon nanotubes (CNTs) induced by bubble collapse

Cu–Fe–CNTs and Ni–Fe–CNTs coatings were deposited on gray cast iron by a hydrothermal approach. It was demonstrated that, the flaky graphite of gray cast iron was exfoliated to graphene nanosheets under hydrothermal reactions, and graphene nanosheets were scrolled to CNTs. After high temperature treatments, the volume losses of Cu–Fe–CNTs and Ni–Fe–CNTs coatings were 52.6 % and 40.0 % of gray cast iron substrate at 60 min wear tests, respectively, obviously increasing the wear properties of gray cast iron. During hydrothermal reactions, water jets and shock waves were produced by bubble collapse. Induced by the water jets and shock waves, exfoliation of flaky graphite was performed, producing exfoliated graphene nanosheets. Attacked by the radially distributed water jets and shock waves, graphene nanosheets were curved, shaped to semicircle morphology and eventually scrolled to tubular CNTs.     

Phase transformation of quasicrystals in aluminium-transition metal alloys

Quasicrystals in Al–Mn, Al–Cu–TM (TM = Fe, Cr, Mn and Ru) and Al–Cu–Fe–Cr alloys can undergo two different modes of phase transformation. Discontinuous transformations of quasicrystals are characterized by the existence of a definite reaction front separating the quasicrystalline phase from the resulting crystalline one; the kinetics are controlled by the migration of the reaction front. Continuous transitions, on the other hand, proceed by structural evolution such as modulation or chemical ordering inside the quasicrystalline phase without creating any high-energy interfaces. Both types of transformations are thermally activated and need atomic diffusion.     

Effects of magnetic field on shape evolution of Fe–Co particles in a Cu matrix

The effects of magnetic field on the shape evolution of ferromagnetic fcc Fe–Co particles in Cu–0.83 at.% Fe–1.37 at.% Co alloy single crystals were examined using magnetic anisotropy measurements. The Cu–Fe–Co single crystals were aged at 993 K for 2 h to 24 h under a magnetic field of 10 T parallel to either the [001] or [011] direction. The magnetic anisotropy was examined by measuring magnetic torque around the (100) plane. It was found that the fcc Fe–Co particles are elongated in the direction parallel to the magnetic field. Furthermore, the elongation along [001] is more remarkable than that along [011]. The results are explained quantitatively by considering the minimization of the sum of the interface energy, elastic strain energy and magnetostatic energy of spheroidal particles.     

High-Energy Ball Milling of Some Intermetallics

High-energy ball milling of metallic powders has been used in recent years for the synthesis of alloys through reactions mainly occurring in solid state. The diffusive phenomena accompanying and promoting the reactions of formation are related to the microstructure acquired by the powders as a consequence of the intense mechanical deformations. The process induces a remarkable comminution of powder particles, inside of which domains of nanometric size are formed and compositional variations often occur. Several analytical techniques are suitable for following the structural evolution of the powders during milling. Among them, Mössbauer spectroscopy is suitable for obtaining detailed local information on the atomic arrangement of the treated materials, if one of the constituents is a Mössbauer isotope, and for detecting little changes occurring at an atomic scale. For these reasons Mössbauer spectroscopy is more sensitive than other analytical techniques especially in the early stages of the process. Some recent results are presented regarding in particular the Fe–Cu, Fe–Al, Fe–Al–Cu, NiAl(Fe) and Fe–Mn systems.     

Thermo-physical properties of ternary Al–Cu–Fe alloy in liquid state

ABSTRACT

The thermodynamic and surface properties of the ternary Al–Cu–Fe alloy in the liquid state have been computed using different models. The thermodynamic properties, such as activity and excess free energy of mixing and the surface properties, such as surface tension have been calculated. The temperature dependence of activity and surface concentration of the components of the ternary Al–Cu–Fe alloy in fixed proportion of any two components have also been calculated. The surface tension of the alloy with respect to the change in temperature in the range 1823–2073?K has also been studied.     

Precipitate characterisation in metallic systems by small-angle X-ray or neutron scattering

Small-angle scattering enables the extraction of precise, quantitative information about nano-scale precipitate microstructures. It can be used with X-rays (SAXS) or neutrons (SANS). This paper presents simple methods for extracting information on the precipitate size and volume fraction from SAS spectra. The various possibilities for obtaining precipitate size are reviewed, and the meaning of their differences is discussed. Examples of applications for complex precipitate microstructure measurements are given in the following areas: kinetic in-situ measurements in Fe–Cu and Fe–Nb–C alloys, non-stoichiometric precipitation in an Al–Zn–Mg–Cu alloy studied by anomalous SAXS (ASAXS), and precipitation mapping in weld cross-sections.     

Monte Carlo simulation of the kinetics of decomposition and the formation of precipitates at grain boundaries of the general type in dilute BCC Fe–Cu alloys

The kinetics of decomposition of a polycrystalline Fe–Cu alloy and the formation of precipitates at the grain boundaries of the material have been investigated theoretically using the atomistic simulation on different time scales by (i) the Monte Carlo method implementing the diffusion redistribution of Cu atoms and (ii) the molecular dynamics method providing the atomic relaxation of the crystal lattice. It has been shown that, for a small grain size (D ~ 10 nm), the decomposition in the bulk of the grain is suppressed, whereas the copper-enriched precipitates coherently bound to the matrix are predominantly formed at the grain boundaries of the material. The size and composition of the precipitates depend significantly on the type of grain boundaries: small precipitates (1.2–1.4 nm) have the average composition of Fe–40 at % Cu and arise in the vicinity of low-angle grain boundaries, while larger precipitates that have sizes of up to 4 nm and the average composition of Fe–60 at % Cu are formed near grain boundaries of the general type and triple junctions.     

Effect of very small additions on the coercivity of Dy-free Nd–Fe–(Co)–B-sintered magnets

The effect of small substitutions on the coercivity of Nd–Fe–B and Nd–Fe–Co–B-sintered magnets has been investigated. Addition of 0.18 at% Ga was found to be the most effective for improving the coercivity in both Nd–Fe–B and Nd–Fe–Co–B without decreasing much the remanent magnetization. Scanning electron microscopy on Ga-free and Ga-added magnets did not reveal a noticeable difference in phase morphology. However, Fe and especially Co concentrations in the intergranular Nd-rich phase were found to be markedly increased after the small Ga addition. Combined addition of Co with a small amount of Cu did not increase the coercivity of the Dy-free magnets. However, none of the examined very small additives can yet be considered as an alternative to Dy for extending operating temperature range of the high-energy Nd–Fe–B magnets.     

On additional aging-induced hardening of textured ribbon substrates prepared from binary copper-based alloys

The structure and microhardness of textured ribbon substrates made of binary copper-based alloys and annealed in the temperature interval 400–600°C is investigated. The optimal temperature of additional annealing at which the strength of Cu–Fe and Cu–Cr alloys reaches a maximum is determined. From experimental data, recommendations on the optimal deposition temperature of epitaxial buffer layers and superconducting films can be developed.     

The deposition of Fe or Co clusters on Cu substrate by molecular dynamic simulation

A molecular dynamic method is used to simulate the film growth process of Fe or Co clusters depositing on Cu substrate with low energy. The tight-binding (TB-SMA) many-body potential is used to simulate the interaction between atoms. The effects of different incident energies and/or substrate temperatures on the surface roughness, layer coverage function, radial distribution function (RDF), and residual stress are investigated. From the simulation results, as the substrate temperature and/or incident energy is increased, the surface roughness of the grown film could be reduced, and the interface intermixing is increased. Also, as compared to Co–Cu system, Fe–Cu system has better surface roughness, less interface intermixing, and similar radial distribution function as well as average stresses.     

Magnetic and Superconducting Properties of the Heterogeneous Layered Structures V/Fe0.7V0.3/V/Fe0.7V0.3/Nb and Nb/Ni0.65(0.81)Cu0.35(0.19)

Journal of Experimental and Theoretical Physics - The heterogeneous ferromagnetic–superconducting layered heterostructures V/Fe0.7V0.3/V/Fe0.7V0.3/Nb and Nb/Ni0.65(0.81)Cu0.35(0.19), which...     

Structural and Mössbauer studies of aerosol FeCu nanoparticles in a wide composition range

Structure and magnetic state of aerosol FeCu nanoparticles of 10–30 nm size with Cu content of 0.6–92.1 at.% have been examined by X-ray diffraction and Mössbauer spectroscopy. The FeCu particles have been shown to consist of an iron core surrounded by a copper and Fe oxide shell. With increasing Cu content the iron core having a bcc structure is reduced down to its complete disappearance followed by vanishing ferromagnetism of the particles. Within the copper content from 4.9 to 74.3 at.% the bcc and fcc phases coexist, with the fcc phase having a lattice constant close to that of pure copper and the bcc lattice constant being slightly higher than that for pure Fe due to embedding Cu atoms into the Fe lattice. At Fe-rich FeCu samples a presence of two-spin (ferromagnetic and paramagnetic) components of the fcc Fe is also observed. In the case of a thin copper shell there is only the ferromagnetic fcc Fe, whereas with further thickening of the shell both spin states of the fcc Fe appear existing up to a 20% Cu content. For FeCu samples with a higher Cu content they disappear due to oxidation of the copper grains. The Cu-rich samples with Cu content higher 80 at.% have a fcc structure, with the lattice constant being slightly higher than that of copper and they are paramagnetic. A slight increase of the lattice constant is due to the penetration of small iron aggregations into the Cu grains. In contact with air, the FeCu particles become covered with Fe₃O₄ and Cu₂O. Their long-term exposure to ambient conditions leads to further oxidation process of Cu₂O to CuO.