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.     

Influence of Al and Ni on the magnetic properties of Finemet alloys

Crystallization behavior and soft magnetic properties of the FeSiBCuNbM (M=Al or Ni) Finemet alloys are investigated by X-ray diffraction, differential scanning calorimetry, hysteresis loop tracer, and vibrating sample magnetometry. The nanocrystalline alloys are prepared by annealing melt-spun amorphous ribbons at different temperatures. Results indicate that the partial substitution of Ni or Al for Nb results in the increase of saturation magnetic induction density (B_s) of the alloys. The alloys with Al or Ni show favorable combination of soft magnetic properties. The partial substitution of Ni for Nb enhances the B_s value, while Al decreases coercivity. The mechanism underlining the magnetic behavior is discussed.     

Effect of alloying on the structure and phase transformations in Ni-Mn alloys alloyed by titanium

The crystal structure of NiMn alloy alloyed by titanium in a wide range of temperatures and compositions has been investigated using resistivity measurements, transmission electron microscopy, electron diffraction, and X ray diffraction. It is found that alloying by titanium not only decreases the martensitic transformation temperature but also changes the martensite crystal structure. The martensitic transformation temperatures are determined and the diagram of martensitic transformations for Ni₅₀Mn_{50 ? x} Ti _x alloys is constructed.     

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.     

On the magnetic properties of mechanosynthesized Co-Fe-Ni ternary alloys

X-ray diffraction, Mössbauer spectroscopy and magnetization measurements were used as complementary methods to obtain structural data and to determine magnetic properties of the mechanically synthesized and subsequently thermally treated Co-Fe-Ni alloys. New, however approximate, phase diagrams were established on the basis of X-ray diffraction investigations. Mössbauer spectroscopy and magnetization measurements allowed to reveal practically linear correlation between the average values of the hyperfine magnetic field induction, 〈B_hf〉, and the effective magnetic moments, μ_eff, of the alloys. The decrease in 〈B_hf〉 with the number of electrons per atom, e/a, was observed. Moreover, the dependence of μ_eff on the valence 3d and 4s electrons per atom follows the Slater-Pauling curve. Thermal treatment of mechanosynthesized Co-Fe-Ni alloys led to some changes in the phase diagrams, increase in the grain size and decrease of the level of internal strains in alloys. Dependencies of lattice constants, average hyperfine magnetic fields, effective magnetic moments and Curie temperatures on the number of electrons per atom have the same trends for mechanically synthesized as well as for thermally treated alloys.     

Structure and thermoelastic martensitic transformations in ternary Ni–Ti–Hf alloys with a high-temperature shape memory effect

The effect of alloying by 12–20 at % Hf on the structure, the phase composition, and the thermoelastic martensitic transformations in ternary alloys of the quasi-binary NiTi–NiHf section is studied by transmission electron microscopy, scanning electron microscopy, electron diffraction, and X-ray diffraction. The electrical resistivity is measured at various temperatures to determine the critical transformation temperatures. The data on phase composition are used to plot a full diagram for the high-temperature thermoelastic B2 ? B19’ martensitic transformations, which occur in the temperature range 320–600 K when the hafnium content increases from 12 to 20 at %. The lattice parameters of the B2 and B19’ phases are measured, and the microstructure of the B19’ martensite is analyzed.     

The magnetic structures of HoTiO3 and ErTiO3

The magnetic structures of rare-earth titanium perovskites, ErTiO₃ and HoTiO₃, have been determined at 4.2 K by neutron diffraction. The Er³⁺ moment of (8.5 ± 0.5) μ_B lies along [001] and is colinear with the titanium moment of (-0.7 ± 0.3) μ_B. The Ho³⁺ moment of (8.1 ± 0.5) μ_B is inclined at an angle of 24° to the bc plane and 32° to the ab pla so as to produce an antiferromagnetic ordering of the x component and a ferromagnetic ordering of the y and the z components. The titanium moment of (-0.55 ± 0.3) μ_B lies in the bc plane but its precise direction has not been determined.     

Ab-initio study of structural,electronic, elastic and mechanical properties of RuAl1−xGax (x=0, 0.25, 0.50, 0.75 and 1)

We have used special quasirandom structure to study the structural, electronic, elastic and mechanical properties of RuAl_1−xGa_x alloys for different compositions (x=0, 0.25, 0.50, 0.75 and 1) using a FP-LAPW method based on Density Functional Theory. The exchange and correlation potential is treated within the generalized gradient approximation. Ground state properties such as lattice constant (a₀), bulk modulus (B), its pressure derivative (B′) and elastic constants are calculated. The ductility of these alloys has been analyzed by calculating the ratio of B/G_H, Cauchy pressure (C₁₂–C₄₄) and Frantsevich rule. From this study RuAl and RuGa are found to be brittle, but their alloys show ductile behavior; RuAl_0.50Ga_0.50 is found to be most ductile. Mechanical properties such as Poisson's ratio (σ), Young's moduli (E), and the ratio of elastic anisotropy factor (A) are estimated. We have also correlated the ductility and bonding behavior of these alloys.     

Heterogeneous nucleation of martensite on precipitates and the martensitic-transformation kinetics in shape memory alloys

The formation of martensite in an elastic stress field near a disk-shaped coherent precipitate is discussed in terms of the theory of diffuse martensitic transformations. The heterogeneous martensite nucleation on precipitates is found to increase the characteristic martensitic-transformation temperature, which increases linearly with the volume density of precipitates. The theoretical results are illustrated quantitatively using the example of the B2 → R phase transition in titanium nickelide alloys.     

Formation of nanostructured states in ternary TiNiFe-based shape memory alloys during megaplastic deformation and subsequent heat treatment

The ternary metastable TiNiFe alloys that exhibit a low-temperature shape memory effect and are subjected to plastic deformation by rolling or high-pressure torsion followed by heat treatment are studied by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and electrical resistivity measurements. It is found that moderate plastic deformation of a Ti₅₀Ni₄₉Fe₁ alloy at room temperature initiates the thermoelastic B2 ? B19’ martensitic transformation and the formation of a developed banded dislocation and twin substructure in the B19’ martensite. This deformation of a Ti₅₀Ni₄₇Fe₃ alloy forms a similar dislocation substructure but in B2 austenite. Megaplastic deformation by high-pressure torsion causes amorphization in the Ti₅₀Ni₄₉Fe₁ alloy and nanofragmentation in the Ti₅₀Ni₄₇Fe₃ alloy. The evolution of the nanostructure and the martensitic transformations in TiNiFe-based ternary alloys is studied during plastic deformation and subsequent annealing at various temperatures.     

Investigation of X-ray diffraction and positron life times in Fe78Si9B13 alloys of amorphous and crystalline structures before and after hydriding

Measurements of mean positron life-times and X-ray diffraction were carried out in unhydrided alloys Fe₇₈Si₉B₁₃ of amorphous and crystalline structures, and after hydriding them. The process of hydriding was carried out at a pressure of 55.773 × 10⁵ N/m². during 168 h. The crystalline samples were obtained after annealing the amorphous alloy Fe₇₈Si₉B₁₃ at 673, 773 and 873 K, respectively. The results obtained after the hydriding process suggest thatan additional electron energy band is formed due to introducing hydrogen inside the samples. The annealing process shows that there exists a nonmonotonic relation between the concentration of free electrons and the degree of order to the structure.     

High pressure X-ray diffraction and electrical resistance study of the quasi-one-dimensional sulfide InV6S8

The ambient structural details and the results of room temperature high pressure angle dispersive X-ray diffraction and electrical resistance measurements on the quasi-one-dimensional sulfide, InV₆S₈, to a pressure of 25 GPa are reported. The material does not undergo a phase transition in this pressure range, though an anomaly in the c/a ratio has been observed around 10 Gpa. A fit of the Murnaghan equation of state to the V/V₀ versus pressure data, with the value of the derivative of B₀ with respect to pressure, B′₀, fixed at 4 has yielded a value of the bulk modulus, B₀, of 110 GPa. We also present data of the pressure dependence of the lattice constants, a and c, the ratio c/a, and the resistance at room temperature.     

High pressure X-ray diffraction study on icosahedral boron arsenide (B12As2)

The high pressure properties of icosahedral boron arsenide (B₁₂As₂) were studied by in situ X-ray diffraction measurements at pressures up to 25.5 GPa at room temperature. B₁₂As₂ retains its rhombohedral structure; no phase transition was observed in the pressure range. The bulk modulus was determined to be 216 GPa with the pressure derivative 2.2. Anisotropy was observed in the compressibility of B₁₂As₂—c-axis was 16.2% more compressible than a-axis. The boron icosahedron plays a dominant role in the compressibility of boron-rich compounds.     

Antiferromagnetic spin correlations in palladium-based Pd-Fe, Pd-Fe-Ag, and Pd-Fe-Rh magnetic alloys

The magnetic structure of Pd_1?x Fe_x (x=0.03, 0.06, 0.10, 0.15, and 0.20) alloys is investigated using the method of ⁵⁷Fe-Mössbauer spectroscopy. The distribution functions P(B _hf) of hyperfine magnetic fields have a discrete structure defined by variations of the contribution to B _hf from the magnetic moment of the neighboring Fe atoms. The anomalies of intensities of components of the functions P(B _hf), which increase with the concentration of iron, are indicative of the instability of configurations with a large total spin and of the formation of local spin configurations with the antiferromagnetic orientation of magnetic moments. The probability of formation of such configurations is defined by the competition of the ferromagnetic Fe-Pd exchange interaction with the direct antiferromagnetic exchange between the nearest neighboring atoms of Fe. An Ag or Rh impurity effectively induces the process of spin flipping, which explains the anomalously strong effect of impurities on the magnetic ordering temperature. The results confirm the presence in Pd-Fe alloys of perturbations of long-range ferromagnetic order revealed by neutron diffraction.     

Elastic properties and phonon dispersions of rhenium in hexagonal-close-packed structure under pressure from first principles

The elastic properties of the hexagonal-close-packed (hcp) structure rhenium (Re) and their behavior under pressure are investigated using the local density approximation (LDA) and the generalized gradient approximation (GGA). The obtained high pressure elastic constants are well consistent with previous theoretical date, while large discrepancies are found between theory and the high pressure experiments. The calculated isothermal bulk modulus B₀ (376 GPa for GGA and 389 GPa for LDA) and its initial pressure derivative (4.52 for LDA and 4.58 for GGA) compare favorably with the experimental values. Moreover, it is found that the value of c/a, B/G, Poisson's ratio, and B_c/B_a are virtually independent of pressure. We also performed calculation for phonon dispersions at high pressure. GGA in our calculation exhibits a same trend as the high pressure experimental curve.     

Enhanced superconductivity of the Ti-Zr alloys in the high-pressure BCC phase

A high-pressure study of the crystal structure and superconductivity of Ti-Zr alloys demonstrates an increase in the ω-β-transition pressure from about 30 to 43–57 GPa when the titanium content in the alloys increases from 0 to 50 at. %. The isobaric values of the BCC β-phase superconducting temperature (at 46 GPa) increase from 5.7 to more than 15 K between 0 and 50 at. % Ti, the latter value being the absolute maximum for BCC d-metal alloys. These data correlate with the earlier assumption of an s-d electron transfer in Zr under pressure.     

Short range order in (Ni65Fe35)77B23 metallic glass by neutron diffraction

The S(Q) structure factor of (Ni₆₅Fe₃₅)₇₇B₂₃ metallic glass was measured by time-of-flight neutron diffraction up to 24 Å^?1 momentum transfer. The distribution of transition metal-boron and transition metal-transition metal first neighbour atom pairs is resolved in the distribution function obtained from S(Q) by Fourier transformation. The distances of these first neighbours pairs, the width of their distribution, the partial coordination numbers and the short range order parameter are given. The results on (Ni₆₅Fe₃₅)₇₇B₂₃ and on the previously studies Fe₈₁B₁₉ amorphous alloys are compared.     

The magnetic entropy changes in Gd1−xBx alloys

A series of Gd_(1−x)B_x alloys have been prepared by arc melting method. After introducing small quantity of B atom in Gd, the Curie temperature of these alloys increase while the magnetic entropy changes are almost same as that of Gd. The refrigerant capacities of these alloys are also greater than that of Gd. These results suggest that Gd_(1−x)B_x alloys may be utilized as refrigerant in household magnetic refrigeration.     

Mössbauer and its r.f. sideband effects in iron-rich glassy alloys

Room temperature Mössbauer and its r.f. induced sideband effects are studied in glassy Fe₄₀Ni₄₀P₁₄B₆ and Fe₈₀P₁₆C₃B₁ alloys in ribbon forms. The direction of the magnetic anisotropy is found to be in the plane of the ribbon for the first alloy while the latter has some out-of-plane anisotropy component. The 3d electronic configuration for iron in the two alloys seems to be about the same in light of the observed isomer shifts and the electron donor model. The r.f. induced sidebands in the spectra are attributed to the magnetostriction of the present alloys.     

Structure of α-FeSi alloys with 8 and 10 at % silicon

The atomic structure of single-crystal samples of Fe_{1 ? x} Si _x (x = 0.08, 0.10) alloys has been investigated using X-ray diffraction. It has been shown that the body-centered cubic (BCC) lattice of these alloys contain clusters with local ordering of the B2 type, which are characteristic of alloys with depleted composition (x = 0.05?0.06). The Fe₃Si phase with the D0₃ structure has been revealed at silicon concentrations x = 0.08 and 0.10. The volume fraction of Fe₃Si-phase regions increases both with an increase in the silicon concentration in the Fe_{1 ? x} Si _x alloy and during annealing of the samples with this silicon concentration at a temperature of 450°C. Based on the results obtained, it has been concluded that the anisotropic distribution of the B2 clusters, which arises as a result of thermomagnetic or thermomechanical treatment, is responsible for the induction and stability of the uniaxial magnetic anisotropy in the Fe_{1 ? x} Si _x (x = 0.05?0.10) alloys.