Vladimir P. Menushenkov

Microstructure and Magnetic Properties of Melt-Spun Nd-Rich Nd-Fe Alloys

The effect of composition on the magnetic properties and microstructure of Nd-rich Nd-Fe alloys prepared by melt-spinning were investigated. Several magnetic phases with ordering temperatures at about 10, 37, 48, and 420-480 K were detected from the temperature dependence of magnetization. The first transition is due to the presence of the double-hexagonal-close-packed Nd phase. The magnetic transitions at 37 and 48 K may be related to the face-centered-cubic Nd-based phase and the Nd-rich nanocrystals. The high-temperature ferromagnetic-paramagnetic transitions at 420-480 K may be connected with the amorphous-like Fe-Nd phase enriched in Fe, which is observed by transmission electron microscopy in the intergranular regions. At temperatures below 100 K, the magnetization of the Nd-Fe ribbons did not saturate in a magnetic field as high as 7200 kA/m. The correlations between the microstructure and coercivity of the Nd-rich Nd-Fe ribbons are discussed.

Mechanochemical Synthesis of Nanocrystalline (Fe,Co)3О4-Based Alloys and their Magnetic Properties

The structure of nanocrystalline Fe-Co-O alloys produced by high-energy ball milling and subsequent low-temperature annealing were investigated by X-ray diffraction analysis, scanning and transmission electron microscopy. The magnetic properties were measured in vibrating sample magnetometers at room temperature. The mixtures of FeO and Co powders were used as starting materials. The nanocrystalline composite alloys, obtained as a result of the milling, contained FeO and -Fe with the crystallite size of 12-18 nm as well as an amorphous phase. However, alloys subjected to subsequent annealing contained Fe3O4 and -Fe phases with crystallite size of 10-30 nm, in which Co is dissolved. Unlike the starting materials the produced powders exhibit properties typical of magnetically hard alloys. The intrinsic coercive force of the annealed powders increases with increasing (Fe,Co)3O4 phase content and reaches approximately 800 Oe.

Local structure of high-coercivity Fe-Ni-Al alloys

Results of hard magnetic Fe-Ni-Al alloys after various thermal processing local structure researches by method of EXAFS-spectroscopy with use of synchrotron radiation at temperature 77 K are presented. It is established, that during cooling a firm solution with critical speed reorganization of a local environment of nickel relative to quickly tempered sample owing to stratification of a firm solution is observed. The subsequent aging at 780?C practically restores local structure, characteristic for quickly tempered sample, keeping thus rather high coercitive force.

Phase Composition and Magnetic Properties of Nd2Fe14B/α-Fe Nanocomposites Prepared by Mechanical Alloying

Combined studies of hard magnetic Nd2Fe14B/α-Fe nanocomposites are performed. They were prepared by mechanical alloying of melt-quenched Nd7.4Pr2.0Fe76.6Co4.2Zr3.4B6.4 and Nd5.8Fe80Co4.9Ti1.5Si2.5B5.3 alloys taken in mass proportions of 90/10 and 70/30. It is found that, after mechanical alloying, an amorphous–crystalline structure is formed; it consists of the hard magnetic Nd2Fe14B and soft magnetic (amorphous and α-Fe) phases. Subsequent annealing at ~500°C initiates the decomposition of the amorphous phase and the formation of the nanocrystalline Nd2Fe14B and α-Fe phases. This leads to an increase in the coercivity and the residual magnetization-to-saturation magnetization ratio (σr/σs ≥ 0.5). It is assumed that the magnetic hardening of powders is due to the formation of an exchange-coupled state, which results from the exchange interaction between α-Fe nanocrystals and the Nd2Fe14B phase.

Structural and Magnetic Properties of As-Cast Fe–Nd Alloys

The effect of composition on the magnetic properties and microstructure of as-cast Nd–Fe alloys was investigated. The temperature dependence of the hysteresis loops was studied. The magnetic phases with ordering temperatures in the range from 7 to 50 K and from 420 to 580 K are detected from zero-field cooled (ZFC) and field cooled (FC) dependencies of magnetization. At temperatures below 100 K, the increase of the magnetizing field leads to a sharp increase of the magnetization, which does not saturate in the magnetization field 90 kOe. The correlations between the microstructure and coercivity of the as-cast Nd–Fe alloys are discussed.

Formation of iron borides and iron nitrides in interaction of iron powder with boron nitride powder

ABSTRACT The paper considers a way of iron nitrides production in monolithic specimens. The relevance for iron nitrides production is conditioned by the promise in using phase Fe16N2 (α’’-phase) as a hard-magnetic material due to the high value of the saturation magnetization (2.3 T at 4.2 K). By means of X-ray diffraction analysis, scanning electron microscopy, and magnetic parameter measurements, the study analyzes the structure and magnetic properties of metal alloy based on iron, obtained as a result of interaction between iron and boron nitride powders after their mixing, pressing, and heat treatment at 1550°C in the atmosphere of nitrogen. The heat treatment results in metal fragments exudation from the ceramic part of the briquette. The microstructure of the fragments is composed of primary deposited iron, eutectic colonies of Fe – iron boride type, and incorporation of iron nitrides. The obtained metal fragments are characterized by high coercivity (0.50 kOe).

Structure and magnetic properties of the Nd 9.5 Fe 84.5 B 6 alloy subjected to severe plastic deformation and annealing

The effect of severe plastic deformation (SPD) by torsion and subsequent annealing on the structure and magnetic properties of the cast Nd9.5Fe84.5B6 alloy is studied. SPD by torsion is shown to lead to partial amorphization of the Nd2Fe14B phase and the precipitation of α-Fe; subsequent annealing results in the crystallization of the amorphous phase and the formation of a nanocomposite Nd2Fe14B/α-Fe structure. After SPD by torsion at 20 revolutions and annealing at 873 K, the (101) texture is formed; in this case, the coercive force is Hc = 360 kA/m and the maximum energy product is (BH)max = 166 kJ/m3. The residual magnetization and the squareness ratio of the hysteretic loop of the textured alloy decrease as the ambient temperature decreases.

Formation of High-Coercivity State in Fe2NiAl Alloy During Decomposition of Solid Solution Under Quenching from Liquid State and Subsequent Annealing

The methods of transmission electron microscopy, atomic force microscopy, x-ray diffraction, and magnetic measurements were used to study the laws of formation of the microstructure and magnetic properties in Fe2NiAl (alni) alloy after quenching from liquid state and subsequent annealing at 500 – 780°C. The microstructure of rapidly hardened flakes is characterized by the presence of inhomogeneities less than 10 nm in size and boundaries of anti-phase domains. Annealing of the flakes is accompanied by their discontinuous decomposition, which causes growth of the colonies comprising alternating plates of β′ andβ2′

Investigation of the structure and magnetic properties of metastable phases in Fe–B alloys melt spun

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