Natalia B. Kolchugina

Electron microscopy, X-ray fluorescence, gas, and X-ray diffraction analyses, and magnetometry are used to study the chemical and phase compositions and magnetic properties of a powder prepared by crushing and subsequent milling of end-of-life Nd–Fe–B sintered magnets, which is performed in an isopropyl alcohol medium. The milling processes used for the preparation of powder are among those comprising the manufacturing procedure of sintered NdFeB permanent magnets by powder metallurgy and should not change the phase composition of the alloy. The maximum powder particle size obtained after milling of the waste sintered permanent magnets is 50 μm. The prepared powder is found to be characterized by an increased oxygen content. The phase composition (wt %) comprises 82.0 % Nd₂Fe₁₄B, 9.7% Nd(OH)₃, 8.0% α-Fe, and 0.3% Nd₂O₃. The oxide phases are present at the powder particle surface. The powder material is shown to have the sufficiently high level of magnetic properties. The possibility of application of the powder in manufacturing sintered permanent magnets, in particular, by 3D printing technology is discussed.

Manufacturing foundations for maintaining a single-crystal structure in rolled thin sheets (0.5 mm thick) prepared from a high-purity [110] molybdenum single crystal grown by electron-beam zone melting are reported. The sheets are manufactured from plate workpieces cut from the single crystal using cold rolling (350°C); a reduction per pass of 5, 10, and 15% to a total strain of 50–75%; and intermediate and final annealing. The maximum scatter of the [001] orientation in the rolled sheets is 3.42°; after final annealing, it is 2.64°. The substructure is studied, and the microhardnesses of the single-crystal plate workpieces (≈177 HV0.5), the final-thickness rolled sheets (≈199 HV0.5), and the sheets subjected to final annealing (≈190 HV0.5) are estimated.

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At the end of lifetime of various facilities, a great amount of worked-out permanent magnets forms, which no longer in practice and are industrial wastes. The reuse of these wastes in manufacturing NdFeB sintered permanent magnets (so-called recycling) would substantially decrease the cost of the magnets, which are usually prepared from not only expensive but also deficient initial components. The modern research methods, such as the electron microscopy, X-ray fluorescence, gas, and X-ray diffraction analysis and magnetometry are used to study the chemical and phase compositions and magnetic properties of powder prepared by crushing and subsequent milling in an isopropyl medium of waste NdFeB sintered magnets. The used crushing and milling processes are one of processes comprising the manufacturing procedure of sintered permanent NdFeB magnets by powder metallurgy and should not change the phase composition of the alloy. The maximum powder particle size obtained after milling the waste sintered permanent magnets was 50 µm. The prepared powder was found to be characterized by the increased oxygen content. The phase composition (wt. %) comprises 82.0 % Nd2Fe14B, 9.7 % Nd(OH)3, 8.0 % α-Fe, and 0.3 % Nd2O3. The oxide phases are present at the powder particle surface. The powder material is shown to be characterized by sufficiently high level of magnetic properties. The possibility of application of the powder in manufacturing sintered permanent magnets, in particular, by 3D printing technology is discussed.

The finite element micromagnetic simulation is used to study the role of complex composition of 2:17R-cell boundaries in the realization of magnetization reversal processes of (Sm, Zr)(Co, Cu, Fe)_z alloys intended for high-energy permanent magnets. A modified sandwich model is considered for the combinations of 2:7R/1:5H phase and 5:19R/1:5H phase layers as the 2:17R-cell boundaries in the alloy structure. The results of the simulation represented in the form of coercive force vs. total width of cell boundary showed the possibility of reaching the increased coercivity at the expense of 180°-domain wall pinning at the additional barriers within cell boundaries. The phase and structural states of the as-cast Sm_1-xZr_x(Co_0.702Cu_0.088Fe_0.210)_z alloy sample with x = 0.13 and z = 6.4 are studied, and the presence of the above phases in the vicinity of the 1:5H phase was demonstrated.

We show here that palladium-lutetium foil Pd–11.2 wt % Lu membrane can be efficiently used for hydrogen separation via its diffusion at temperatures 300–500°С. Several correlations of the membrane structure morphology and the specific permeability of the membranes are considered. Particular attention is placed in analysis of the membrane surface studied by atomic force microscopy using the phase contrast mode. The studies performed are addressed the problem of the membrane durability for the cyclic operation up to 40 h in hydrogen atmosphere.

In present study, X-ray diffraction and local electron probe microanalysis are used to identify microstructural and phase features of as-cast (Sm,Zr)(Co,Cu,Fe)_z alloys used for manufacturing high-coercivity permanent magnets. The structure of the as-cast alloys, which were prepared in the wide composition range corresponding to the coexistence of the 2:17 and 1:5 phases, is studied in detail. The 2:17R, 1:7H, 1:5H, 5:19R, 2:7R, 2:7H, 1:3R, and 1:3H phases were identified and are shown to be simultaneously present in the as-cast state owing to the nonequilibrium phase transformations occurred upon solidification of the ingots.

X-ray diffraction and differential thermal analyses are used to study multicomponent Nd–R–Fe–B (R = Pr, Ce, La) alloys prepared by induction melting in an inert gas atmosphere and subsequent forced cooling upon casting in a massive cast iron mold. The effect of substitution of light rare-earth metals for neodymium on the phase composition and morphology of the cast alloys with 0–6.9 wt % Pr, 0–10.0 wt % Ce, and 0–9.0 wt % La, which are used as precursors in manufacturing sintered permanent magnets with high hysteretic characteristics, is studied. The main structural constituents of the alloys are shown to be a magnetic phase with the Nd₂Fe₁₄B-type structure and Nd-rich, R_1.1Fe₄B₄, and R₂Fe₁₇ phases. The phase transformation temperatures of the alloys are determined, which allow us to correct the sintering temperatures of permanent magnet powder blanks prepared from the cerium- and lanthanum-containing alloys.

The purity of hydrogen, which is an alternative energy carrier in powder sources of distributed energy resource systems and, in particular, is the feed stock for fuel cells, should be no less than 99.9999 vol % purity High-purity hydrogen can be prepared only via its separation as a result of selective diffusion through metallic membranes manufactured from specific membrane palladium-based alloys prepared in the form of thin foils. In the present work, the combination of deformation and annealings under different conditions is used to prepare the Pd–7.70 wt % Lu alloy in the form of foil 50 µm thick, whose specific hydrogen permeability is studied in the course of cyclic heating and cooling in a hydrogen atmosphere in a temperature range of 300–500°С. The Pd–7.70 wt % Lu membrane is shown to demonstrate high and stable hydrogen permeability. The evolution of the surface structure of the membrane in the course of its operation in the hydrogen atmosphere is studied by atomic force microscopy using the phase contrast mode.

Experimental series of alloys for (Sm,Zr)(Co,Cu,Fe)_Z permanent magnets are presented in the concentration ranges that provide wide variations of (4f)/(4d)/(3d) ratios of comprising elements. Optical metallographic analysis, observation of the surface domain structure upon magnetization reversal (Kerr effect), electron microprobe analysis, and measuring the major hysteresis loops of samples at different stages of heat treatment are used to study processes related to the development of the highly coercive state of these samples. It was found that the volume fractions of two main structural components A and B, which comprise 90% of the total sample volume, rigorously control the coercivity at all stages of thermal aging. At the same time, structural components A and B themselves in samples being in the high-coercivity state differ qualitatively and quantitatively in the chemical composition, domain structure and its development in external magnetic fields and, therefore, are characterized by different morphologies of the phases comprising the structural components. Two stages of phase transformations in the sample structure are observed. During isothermal annealing, the cellular structure develops within the B component, whereas, during stepwise (slow) cooling or quenching from the isothermal aging temperature to 400 °C, a phase structure evolves within both the cell boundaries in B and the structural component A. The degree of completion of the phase transformations within micro- and nano-volumes of the components determines the ultimate hysteretic characteristics of the material.