N. M. Kleinerman

Structure and magnetic properties of nanocrystalline FeCuNbSiB alloys after a thermomechanical treatment

The peculiarities of the formation of a nanocrystalline structure and induced magnetic anisotropy have been studied in Fe87−xCu1Nb3SixB9 alloys (x = 0, 4, 6, 8, 9.5, 11, 13.5 at. %) after thermomechanical treatment. Differences in the dynamics of the process of phase separation in the initial amorphous state, final phase composition, and magnitude and sign of induced magnetic anisotropy have been revealed depending on the initial content of silicon.

High-strength magnetically hard Fe-Cr-Co-Based alloys with reduced content of chromium and cobalt

Structure and magnetic and mechanical properties of precipitation-hardening Fe-Cr-Co-W-Ga alloys with reduced Cr and Co contents have been studied. The compositions studied go beyond the limits of the miscibility gap in the phase diagram for conventional Fe-Cr-Co alloys. It has been established that after cold plastic deformation and low-temperature annealing the alloys are characterized by high values of mechanical and magnetic characteristics, which are significantly higher than those of known analogs. It is demonstrated that the treatment suggested leads to the decomposition of homogeneous solid solution based on α-Fe with the precipitation of disperse particles of a tungsten-rich phase, which promotes strengthening of alloys.

Thermomagnetic and Mössbauer studies of structural transformations caused in the amorphous Nd9Fe85B5 alloy by severe plastic deformation and annealing

Thermomagnetic analysis and Mössbauer spectroscopy were used to study the effect of severe plastic deformation (SPD) by high-pressure torsion (HPT) and subsequent annealing on structural transformations and formation of magnetic properties of rapidly quenched Nd9Fe85B6 alloy. The HPT of the Nd9Fe85B6 amorphous alloy was found to result in the precipitation of α-Fe nanocrystals and in changes in the structural state of the residual amorphous phase A′. In the annealed samples, there was revealed a great amount of nonequilibrium phases with different magnetizations. The total content of nonequilibrium phases depends on the annealing temperature and affects the exchange interaction between magnetically soft α-Fe nanocrystals and Nd2Fe14B nanocrystalline grains. The results obtained in this study can explain the differences between the high level of hysteresis properties of nanocrystalline materials, which was predicted theoretically, and low magnitudes realized in practice.

Structural transformations in high-strength magnetically hard Fe-Cr-Co-W-Ga alloys

Processes leading to a high-coercivity state of W and Ga containing Fe-Cr-Co alloys that possess a required strength and plasticity have been investigated. The effect of W and Ga additions on the structural constituents formed due to the decomposition of a high-temperature solid solution has been studied by the methods of X-ray diffraction, electron microscopy, and Mössbauer spectroscopy. The role of cold deformation preceding low-temperature annealings has been clarified.

Mössbauer Studies of the Magnetic Phase Transition in La(Fe 0.88 Si x Al 0.12 - x ) 13 Compounds

Spectra of the nuclear gamma resonance for La(Fe0.88SixAl0.12 − x)13 compounds with different x values have been measured at 100 K. The compounds exhibit an antiferromagnetic ordering in the range of silicon concentrations x ≤ 0.024 and a ferromagnetic ordering at x > 0.024. Analysis of the spectra has been carried out with the use of a two-core distribution of quadrupole shifts. It has been demonstrated that upon a transition from antiferromagnetic to ferromagnetic ordering, the average hyperfine field at the Fe nuclei increases by almost 40 kOe. It has been found that antiferromagnetic compounds are mainly characterized by a positive quadrupole shift, and ferromagnetic ones by a negative quadrupole shift. A model of the formation of a magnetic structure that explains the appearance of a layered antiferromagnetic ordering in La(Fe0.88SixAl0.12 − x)13 compounds has been proposed.

Effect of tungsten and gallium on the structure and magnetic and mechanical properties of Fe-Cr-Co alloys

Effects of the alloying additions of W and Ga, cold deformation, and regimes of heat treatment on the magnetic and mechanical properties of precipitation-hardening Fe-Cr-Co alloys have been investigated. It has been shown that the alloying with tungsten leads to a strengthening of the α solid solution and an additional jumplike increase in strength after deformation and age hardening. The coercive force grows simultaneously with an increase in strength; the structure of the alloy in this case contains a large concentration of linear defects (dislocations), which indicates an important contribution of magnetoelastic energy to the formation of the high-coercivity state and of elastic strains to the increase in the strength properties. The character of fracture becomes brittle. The modifying of the alloy with gallium leads to an increase in plasticity due to the dispersion of the structure, formation of retained austenite in it, and formation of an interphase layer more uniform in composition. The character of fracture changes from brittle to brittle-ductile. A high-strength magnetically hard material has been obtained with Hc = 90–125 A/cm, σm = 120–130 G cm3/g, Br = 0.6–0.65 T, σ0.2 = 1300–1600 MPa, and δ = 2.0–4.6%.

Magnetic phase transitions in the Ce(Fe1 − xSix)2 compounds

The structure of the Ce(Fe1 − xSix)2 compounds (with x ≤ 0.075) has been studied and, magnetic susceptibility, heat capacity, and Mössbauer effect have been measured. The compounds with x ≥ 0.05 are antiferromagnetic at low temperatures; as the temperature increases, the compounds become, at first, ferromagnetic and next paramagnetic. The temperatures of magnetic phase transitions have been determined using data on the magnetic susceptibility, and the magnetic phase diagram of the system has been constructed. The heat capacity has been measured and the data were used to calculate the entropy change upon magnetic phase transitions; it is 7.9 and 6.0 J/kg K for CeFe2 and Ce(Fe0.93Si0.07)2, respectively. An analysis of Mössbauer spectra for the alloys in the paramagnetic state allowed us to find that silicon atoms statistically substitute for iron atoms in the crystal lattice intermetallic.

Structure of La(Fe0.88SixAl0.12 − x)13 compounds in the paramagnetic state

X-ray diffraction patterns and nuclear gamma resonance spectra of La(Fe0.88SixAl0.12 − x)13 compounds in the paramagnetic state at room temperature have been investigated. It has been found that all samples have a cubic structure of the NaZn13 type, in which Si and Al atoms disorderly substitute for iron in the crystallographic position 96i. An analysis of the Mössbauer spectra using the fitting with doublets with different quadrupole splittings has revealed that the distributions of the aluminum and silicon impurity atoms substituting for iron differ significantly. Aluminum is statistically distributed over nine positions of the 96i type in the generalized coordination sphere of the Fe2 atom, whereas silicon predominantly substitutes for only six of the nine positions.

The role of plastic deformation in the creation of high strength in hard magnetic alloys Fe-Cr-Co-W-Ga

The influence of plastic deformation preceding low-temperature aging on the structural factors that determine the strengthening of the Fe-15Cr-13Co-8W-0.5Ga and Fe-22Cr-l5Co-9W-0.5Ga alloys has been studied. The reasons are discussed for the necessity of employment of different strains to achieve the high-strength state in alloys with different contents of chromium and cobalt.

Moessbauer study of structure changes in Fe-Co-Cr alloys upon their alloying with W and Ga

Changes in the structure of the magnetically hard alloys Fe-Co-Cr alloyed with W and Ga to reach high mechanical properties were investigated. Moessbauer spectra processed in several steps present information on the influence of both different stages of treatment routine and concentration variations on the composition and fine peculiarities of the components that constitute the required structure states.