X-ray diffraction studies of specific features in the atomic structure of Fe-Si alloys in the α area of the phase diagram

The atomic structure of Fe-Si alloys with a silicon concentration of 5–8 at % (α-area of the phase diagram) was studied using X-ray diffraction. The effect of quenching after annealing at a disordering temperature of 850°C on the structural state of the alloys was elucidated. It is shown that the quenched samples are characterized by a short-range ordering; namely, there is a local B2-type order at a concentration of 5–6 at % Si and, in addition, DO₃-phase clusters are formed at 8 at % Si. The atomic structure of B2 clusters and their nearest surroundings is established.     

Electronic structure and magnetism of Co–Fe alloys with short-range order

Using a model which considers the localized and itinerant nature of the 3d electrons, and short-range order correlations, we obtain Co_xFe_1−x binary magnetic alloys electronic structure for different values of concentration x for subsequently finding the magnetic moment behaviour of each of the alloy components as function of the Co concentration x. In this way we are able to obtain results that agree with experiments of polarized neutrons diffraction.     

First principles study on the electronic structure and magnetism of Fe1-xCoxSi alloys

Electronic and magnetic properties of Fe1-xCoxSi alloys were investigated by using a full-potential linear augmented-plane-wave method based on density functional theory. Electronic structure calculation demonstrates that half-metallic property appears in the Fe-rich region of 0 〈 x ≤ 0.25, while the alloys turn out to be a magnetic metal for x 〉 0.25. The concentration dependence of the magnetic moment of the alloys can be understood by the fixed Fermi level at minority band in Fe-rich region, as well as at the majority band in Co-rich region. In Fe-rich alloys, the electronic structure and the magnetic properties at Fe site depend mainly on the spin-polarization of nearest neighbouring Co atoms, while in Co-rich alloys, these features at Co site arise mainly from the neighbours of Fe atoms.     

Pressure dependence of the irradiation-induced ferromagnetism in Fe–Ni invar alloys

Pressure dependence of the irradiation-induced ferromagnetism recently found in Fe–Ni invar alloys was investigated under hydrostatic pressures up to 7.5 GPa. A rectangular sheet of Fe–30.2 at% Ni invar alloy was irradiated with 80 MeV Xe ions. The range was much smaller than the thickness of the sample. The Curie temperature of the irradiated part increased by 63 K, and the absolute value of the pressure coefficient, dT_C/dp   was smaller than that of non-irradiated part. The relation p≈(_TC0-_TC)ⁿ$p\approx (T_{{\mathrm{C}}_0}-T_{\mathrm{C}}{)}^n$ holds with n=2$n=2$ for both non-irradiated and irradiated part. The itinerant character was not so much modified by irradiation.     

Effect of gallium alloying on the structure,the phase composition,and the thermoelastic martensitic transformations in ternary Ni–Mn–Ga alloys

The effect of gallium alloying on the structure, the phase composition, and the properties of quasibinary Ni₅₀Mn_50–zGa_z (0 ? z ? 25 at %) alloys is studied over a wide temperature range. The influence of the alloy composition on the type of crystal structure in high-temperature austenite and martensite and the critical martensitic transformation temperatures is analyzed. A general phase diagram of the magnetic and structural transformations in the alloys is plotted. The temperature–concentration boundaries of the B2 and L2₁ superstructures in the austenite field, the tetragonal L1₀ (2M) martensite, and the 10M and 14M martensite phases with complex multilayer crystal lattices are found. The predominant morphology of martensite is shown to be determined by the hierarchy of the packets of thin coherent lamellae of nano- and submicrocrystalline crystals with planar habit plane boundaries close to {011}_B2. Martensite crystals are twinned along one of the 24 \(24\left\{ {011} \right\}{\left\langle {01\bar 1} \right\rangle _{B2}}\) “soft” twinning shear systems, which provides coherent accommodation of the martensitic transformation–induced elastic stresses.     

Effect of copper on the structure–phase transformations and the properties of quasi-binary TiNi–TiCu alloys

The effect of copper alloying up to 25 at % on the structure–phase transformations and the physicomechanical properties of ternary alloys from the quasi-binary TiNi–TiCu section is studied by measuring the physicomechanical properties, transmission electron microscopy, scanning electron microscopy, electron diffraction, and X-ray diffraction (XRD). The data of temperature measurements of the electrical resistivity and the magnetic susceptibility and XRD data are used to plot a general diagram for the thermoelastic B2 ? B19', B2 ? B19 ? B19', and B2 ? B19 martensitic transformations, which occur in the alloys upon cooling as the copper content increases in the ranges 0–8, 8–15, and 15–25 at % Cu, respectively. The experimental results are compared to the well-known data, including differential scanning calorimetry data, obtained for these alloys. The changes in the mechanical properties and the microstructure of the alloys in the state of B19 or B19' martensite are discussed.     

Magnetic Thermocouples Made of Co–Fe and Ni–Fe Permalloys

Technical Physics - Magnetized and unmagnetized Co–Fe and Ni–Fe alloys fabricated on a two-high casting installation in the form of thin flexible amorphous films are promising materials...     

Interdiffusion and solid solution strengthening in Ni–Co–Pt and Ni–Co–Fe ternary systems

Diffusion couple experiments are conducted in Co–Ni–Pt system at 1200?°C and in Co–Ni–Fe system at 1150?°C, by coupling binary alloys with the third element. Uphill diffusion is observed for both Co and Ni in Pt rich corner of the Co–Ni–Pt system, whereas in the Co–Ni–Fe system, it is observed for Co. Main and cross interdiffusion coefficients are calculated at the composition of intersection of two independent diffusion profiles. In both the systems, the main interdiffusion coefficients are positive over the whole composition range and the cross interdiffusion coefficients show both positive and negative values at different regions. Hardness measured by performing the nanoindentations on diffusion couples of both the systems shows the higher values at intermediate compositions.     

The effect of HCP on the formation of twin boundaries and dislocations in Ni–Co alloys

In this study, molecular dynamics (MD) was used to simulate the rapid solidification process of Ni₄₇Co₅₃ and Ni₄₈Co₅₂ alloys at a cooling rate of 10¹² K/s. The effects of HCP on the formation of twin boundaries and dislocations in two Ni–Co alloys are studied. It is found that the difference of HCP clusters is the main effect that producing discrepancies on microstructure of two alloys. The number of HCP clusters accounted for 9.23% in Ni₄₇Co₅₃ alloy. They are regularly arranged to form the number of single-layer twin boundaries, and each twin boundary ends in a dislocation. The FCC and HCP structures coexist in the same atomic layers, which is easy to create dislocations. The relatively standard FCC crystal and only 0.32% HCP clusters are formed in Ni₄₈Co₅₂ alloy at 300 K. That small amount of HCP clusters are dispersed on the surface, and cause the formation of dislocation in the border with FCC clusters.     

Structural and magnetic properties of Fe–Ni mecanosynthesized alloys

Fe_100???x Ni _x samples with x?=?22.5, 30.0 and 40.0 at.% Ni were prepared by mechanical alloying (MA) with milling times of 10, 24, 48 and 72 h, a ball mass to powder mass (BM/PM) ratio of 20:1 and rotation velocity of 280 rev/min. Then the samples were sintered at 1,000°C and characterized by X-ray diffraction (XRD) and transmission Mössbauer spectrometry (TMS). From the refinement of the X ray patterns we found in this composition range two crystalline phases, one body centered cubic (BCC), one face centered cubic (FCC) and some samples show FeO and Fe₃O₄ phases. The obtained grain size of the samples shows their nanostructured character. Mössbauer spectra were fitted using a model with two hyperfine magnetic field distributions (HMFDs), and a narrow singlet. One hyperfine field distribution corresponds to the ferromagnetic BCC grains, the other to the ferromagnetic FCC grains (Taenite), and the narrow singlet to the paramagnetic FCC grains (antitaenite). Some samples shows a paramagnetic doublet which corresponds to FeO and two sextets corresponding to the ferrimagnetic Fe₃O₄ phase. In this fit model we used a texture correction in order to take into account the interaction between the particles with flake shape and the Mössbauer $\upgamma$ -rays.     

The structure and composition of novel electrodeposited Sn–Fe and Sn–Co–Fe alloys from a flow circulation cell system

This study involved the use of a flow circulation cell, using varying circulation rates as a room temperature process (20°C). Mössbauer and XRD analysis were conducted to ascertain whether amorphous or microcrystalline structures could be obtained at 20°C using a range of current densities. Amorphous or microcrystalline structures of Sn–Fe and Sn–Co–Fe have potentially important industrial applications for energy efficient cells, for use as high performance electrodes in lithium batteries, as environmentally acceptable corrosion resistant materials and are derived from an energy efficient environmentally friendly electrolyte process which would be acceptable as an industrial process. $^{\it 57}Fe$ and $^{\it 119}Sn$ Mössbauer investigations supported by XRD analysis confirmed that the room temperature flow circulation cell gave rise to previously unknown non-equilibrium amorphous structures which do not occur in the corresponding thermally prepared alloys as shown in the thermal equilibrium diagrams. Mössbauer analysis shows these alloys to be both amorphous and ferromagnetic. It is shown that the flow circulation cell used at 20°C based on the environmentally friendly gluconate bath reported gives amorphous based Sn–Fe and Sn–Co–Fe alloys over a useful range of current densities facilitated by using a range of circulation rates.     

Precipitation and fracture behaviour of Fe–Mn–Ni–Al alloys

The effects of Al addition on the precipitation and fracture behaviour of Fe–Mn–Ni alloys were investigated. With the increasing of Al concentration, the matrix and grain boundary precipitates changed from L1₀ θ-MnNi to B2 Ni₂MnAl phase, which is coherent and in cube-to-cube orientation relationship with the α′-matrix. Due to the suppression of the θ-MnNi precipitates at prior austenite grain boundaries (PAGBs), the fracture mode changed from intergranular to transgranular cleavage fracture. Further addition of Al resulted in the discontinuous growth of Ni₂MnAl precipitates in the alloy containing 4.2?wt.% Al and fracture occurred by void growth and coalescence, i.e. by ductile dimple rupture. The transition of the fracture behaviour of the Fe–Mn–Ni–Al alloys is discussed in relation to the conversion of the precipitates and their discontinuous precipitation behaviour at PAGBs.     

Abnormal resistivity behavior of Cu–Ni and Cu–Co alloys in undercooled liquid state

The resistivity behavior of undercooled liquid Cu–Ni and Cu–Co alloys had been studied in the contactless method, to probe the structure transition in undercooled melts during the cooling process. Over the entire concentration range, linear behavior of resistivity with temperature was obtained in liquid and undercooled liquid Cu–Ni system. It implied that the formation of icosahedral order might not influence the electron scattering in undercooled liquid Cu–Ni alloys. Similar results were obtained in Cu–Co system in the vicinity of liquidus temperature. A turning point was obvious in temperature coefficient of resistivity for undercooled liquid Cu–Co alloys around the bimodal line, which was interpreted to be responsible for metastable liquid–liquid phase separation. During liquid phase separation process, resistivity decreased and the temperature coefficient of resistivity was larger than that of homogeneous melts. In combination with transmission electron microscopy and scanning electron microscope studies on the as-solidified microstructure, this was interpreted as the formation of egg-type structure and concentration change in Cu-rich and Co-rich phases. The mechanism controlling the separation and droplets motion was also discussed in undercooled liquid Cu–Co system.     

Synchrotron X-ray diffraction studies on the phase transitions in the spinel LixMn3−xO4 intercalation compounds

Detailed investigations have been undertaken of the lithium for manganese substitution effect on the LiMn₂O₄, in the system Li_xMn_3−xO₄, for 0.95≤x≤1.05, that is for the nearly stoichiometric lithium content. Synchrotron X-ray measurements have been performed in the temperature range 10–300 K. The diffraction experiments were carried out at the DESY-HASYLAB high-resolution powder diffractometer (beamline B2), equipped with a closed-cycle He-cryostat. Very small changes in the lithium content influence clearly the low-temperature crystal structure of Li_xMn_3−xO₄, spinels and the nature of phase transitions. It was found that for x=0.95 the sample remains tetragonal in the whole 10–300 K temperature range. The stoichiometric LiMn₂O₄ transforms from cubic to orthorhombic at about 280 K. For x=1.0125 the temperature of phase transition from cubic to orthorhombic decreases down to about 260 K, whereas for x=1.025 the transformation goes from cubic to tetragonal phase, at the temperature 220 K. No phase transition has been observed for the cubic sample with x=1.0375. These results partly explain the divergences in recent reports on the low-temperature structure and phase transformations of lithium manganese oxides.     

On the formation of a phase with tenfold symmetry in amorphous Ni–Zr alloys

The magnetic anisotropy energy (MAE) of 3d transition-metal wires, stripes, and films is calculated self-consistently as a function of stripe width and film thickness. The magnetization-reorientation transitions in stripes are determined along the crossover from the mono-atomic one-dimensional chain to the two-dimensional monolayer. It is shown that the MAE oscillates as a function of stripe width and depends strongly on the considered transition metal. The reorientation transitions in Co films deposited on a highly polarizable substrate such as Pd are discussed. A local analysis of the layer-resolved MAEs provides new insights into the off-plane magnetization observed in Pd-capped Co films on Pd(111). The interfaces responsible for the stability of the off-plane easy axis are characterized microscopically. An unexpected internal magnetic structure of the Co–Pd interfaces is revealed in which the magnetic moments and spin–orbit interactions at Pd atoms play a crucial role. The nature of the reorientation transition from perpendicular to in-plane magnetization with increasing film thickness is studied by means of full-vectorial calculations. The existence of a spin-canted phase at intermediate film thickness is demonstrated.     

Effect of gamma irradiation on the atomic ordering of Fe–Co alloys in nanocrystalline films

The effect gamma irradiation has on the room-temperature atomic ordering in Fe_0.5Co_0.5 and Fe_0.75Co_0.25 single-crystal films is investigated. The possibility of Fe–Co alloys in film samples becoming disordered under the effect of gamma irradiation is revealed. This effect is explained by the effect gamma irradiation has on atomic diffusion.     

Influence of temperature and alloying elements on the threshold displacement energies in concentrated Ni–Fe–Cr alloys

Concentrated solid-solution alloys(CSAs) have demonstrated promising irradiation resistance depending on their compositions. Under irradiation, various defects can be produced. One of the most important parameters characterizing the defect production and the resulting defect number is the threshold displacement energies(E_d). In this work, we report the results of E_dvalues in a series of Ni–Fe–Cr concentrated solid solution alloys through molecular dynamics(MD)simulations. Based on several different empirical potentials, we show that the differences in the E_dvalues and its angular dependence are mainly due to the stiffness of the potential in the intermediate regime. The influences of different alloying elements and temperatures on E_dvalues in different CSAs are further evaluated by calculating the defect production probabilities. Our results suggest a limited influence of alloying elements and temperature on E_dvalues in concentrated alloys. Finally, we discuss the relationship between the primary damage and E_dvalues in different alloys. Overall, this work presents a thorough study on the E_dvalues in concentrated alloys, including the influence of empirical potentials,their angular dependence, temperature dependence, and effects on primary defect production.