Hard Magnetic Alloys Research Articles

Structure and Properties of Additive Hard Magnetic Alloys 25Cr15Co and Alnico

It was studied the structure of hard magnetic alloys Fe-Cr-Co and Al-Ni-Cu-Co-Fe manufactured by selective laser melting (SLM) from spherical powders smaller than 80 microns on the RussianSLM FACTORY unit. Powders were manufactured by melt atomization. At various scanning speeds and laser powers, samples were made to study the structure, magnetic and mechanical parameters. By constructing a hysteresis loop, data were obtained indicating an increase in the magnetic characteristics in SLM samples in comparison with similar ones obtained by foundry technology.

The effect of high-pressure torsion on the structure and long-range order of ferromagnetic τ-MnAl alloy

The aim of this work was to study the effect of high-pressure torsion deformation method on the structure of τ-MnAl hard magnetic alloy. The long-range order parameter σ dependence on strain revealed nonmonotonical behavior with a minimum. A drastic fall in the long-range order parameter occurred due to accumulation of dislocations was detected for all samples deformed up to true strain ε = 4.93 where the minimum of σ = 0.49 was reached. The alloy undergone deformation ε > 4.93 was characterized by partial recovery of σ. Possible structural factors for the long-range order parameter behavior are discussed in the article.

δM plots of nanocrystalline hard magnetic alloys

Magnetic properties of nanocrystalline hard magnetic alloys such as coercivity and maximum energy product are strongly depended on microstructure and interactions between grains. There are a lot of advanced experimental techniques for microstructure characterization but the analysis of intergrain interactions is still challenging. One of the wide-spread methods for doing that is plotting δM(H). This work is aimed to elucidate how different factors effect δM(H) plots for high-anisotropy nanocrystalline alloys. Specifically, changes of δM(H) plots caused by both intergrain exchange and magnetostatic interactions, grain size dispersion, and demagnetization factor are analyzed systematically using macrospin-based simulations. It is demonstrated that all these factors should be considered for a reliable evaluation of exchange coupling in alloys. A concept of such analysis is presented and applied to rapidly quenched Nd-FeCo-B alloy.

The experience of magnets manufacturing from metal powder using a laser

The structure of hard magnetic and soft magnetic alloys manufactured on a RussianSLM FACTORY init by selective laser melting (SLM) from a spherical powder less than 80 μm in size has been studied. The powder is made by melt atomization from ingots. At various scanning speeds and laser power, additive samples were manufactured to study the structure, magnetic parameters, and also fractal analysis. According to the research results, recommendations were given on changing the melting modes and conducting thermal post-processing of materials. By constructing a hysteresis loop, data were obtained indicating the achievement of magnetic characteristics in additive samples that are close in magnitude to magnets of traditional founding technology. Prototypes of complex-shaped additive magnets have been made.

Multifractal analysis and magnetic properties of the "25Х15КА" additive hard magnetic alloy

The preparation of a hard magnetic alloy of the Fe—Cr—Co system by the additive method of selective laser melting of a metal powder obtained by melt atomization is considered. The structures and magnetic parameters of the additive samples are investigated. An increase in the magnetic characteristics of these samples in comparison with cast samples is established. Keywords: selective laser melting, metal powder, structure, multifractal analysis, magnetic properties. npk3@crism.ru

Al–Mn Hard Magnetic Alloys as Promising Materials for Permanent Magnets (Review)

Permanent magnets constitute an important base for advanced technologies. Rare-earth-based alloys are currently the main permanent magnet materials. Due to the limited availability and high costs, these magnets are, as a rule, used in small items. In large-scale equipment (e.g., in generators, motors, including magnetic levitation transport devices), more affordable and cheaper materials are addressed. Manganese-based alloys, in particular, AlMn, may be regarded as examples of these materials. In Russia, extensive research activity into aluminum–manganese alloys was during the period from the 1960s to the 1990s [1–3]. In other countries this research activity has continued till now. More than one hundred articles were published during the last decade. Most of them address bulk and film samples of the metastable magnetic phase τ-AlMn. Our review focuses on an analysis and systematization of contemporary studies into the preparation and properties of manganese–aluminum alloys; perhaps, it will serve to popularize research into manganese-based intermetallics as promising materials for permanent magnets in Russia.

SmFe12-based hard magnetic alloys prepared by reduction-diffusion process

High phase-purity Sm(Fe0.8Co0.2)11Ti and Sm0.8Zr0.2(Fe0.8Co0.2)11Ti powders with the tetragonal ThMn12 crystal structure have been synthesized by reduction-diffusion method. The average particle size is 1.47 ± 0.82 μm for the Zr-free and 2.29 ± 1.22 μm for the Zr-doped samples. The larger particles are multi-grain, without a chemically distinct grain boundary phase as revealed by TEM investigations. The intrinsic magnetic properties are μ0Ms= 1.42 ± 0.04 T, μ0Ha= 9.8 ± 0.4 T for Zr-free and μ0Ms= 1.37 ± 0.04 T, μ0Ha= 9.7 ± 0.4 T for Zr-doped samples. Temperature-dependent XRD studies show that the ThMn12-type phase begins to decompose around 500 °C which presents difficulties for further development into fully dense bulk magnets. Successful introduction of grain boundary phase with good wettability has been realized by infiltrating low-melting eutectic alloys, resulting in fully dense bulk samples. However, coercivity remains low, μ0Hc = 0.34 T. The underlying microstructural reasons for not achieving large Hc are discussed.

Chemical synthesis and research nanopowder of magnetic hard alloy Nd15Fe78B7

Hard magnetic nanopowders of the Nd15Fe78B7 alloy were synthesized by the reduction-diffusion reaction of a stoichiometric mixture of Nd, Fe, and Fe-B oxides with CaH2 in a hydrogen atmosphere at 800 ° C. Nd, Fe, Fe-B oxides were obtained by precipitation and had the form of granules with an average particle size of neodymium oxide - 50 nm, iron oxide - 95 nm, iron borate - 57 nm. The particle size of the Nd15Fe78B7 alloy was 45-140 nm. It is shown that the proposed method is suitable for obtaining nanopowders of hard magnetic alloys of the Nd-Fe-B system.

Structural studies of additive hard magnetic alloy Alnico24

The structure of the hard-magnetic alloy Alnico24 manufactured on the Russian SLM FACTORY selective laser melting unit was studied. Powder for alloying with a fraction of up to 80 μm was obtained by melt atomization from ingots on a HERMIGA 75 / 3VI unit. At various scanning modes and laser power, additive samples were manufactured to the structure studies. Detailed structural studies were performed using multifractal parameterization.

Magnetic properties of the Fe-24%Cr-15%Co-3%Mo-1.5%Ti hard magnetic alloy in anisotropic and isotropic states

The magnetic properties of the Fe-24%Cr-15%Co-3%Mo-1.5%Ti (in wt. %) hard magnetic alloy in anisotropic and isotropic states after various heat treatments were studied. The alloy was prepared by the methods of powder metallurgy. The relative density was 98 %. The coefficient of thermal expansion of the alloy during heating and cooling was 17, 4*10 6 K−1 and 19, 0 *10− 6 K1 in the temperature range of 100 °C - 1300 °C. The kinetics of o-phase formation caused by an isothermal annealing at T = 750 ºC was investigated by means of the hardness measurements. The best magnetic properties of the alloy in anisotropic state were obtained after thermomagnetic treatment with cooling rate 200 ºC/h as Br = 1.22 T, Hc = 42.2 kAm-1 and (BH)max = 31.2 kJm- 3 and on the alloy in isotropic state with cooling rate 40 ºC/h.

Magnetic Hysteretic Properties of an Fe–25Cr–12Co Powdered Hard Magnetic Alloy

The magnetic hysteretic properties of an Fe–25Cr–12Co powdered hard magnetic alloy have been studied as a function of heat-treatment conditions. The optimization of heat treatment, including thermomagnetic process, and the determination of the optimum magnetic hysteretic properties have been performed using the Statgraphics Centurion XVI software. The following parameters are obtained after the optimum heat treatment: the residual induction is up to Br = 1.425 T, the coercive force is HcB up to 46.45 kA/m, and the maximum energy product is (BH)max = 45.2 kJ/m3. Various optimum heat-treatment conditions are required to achieve the optimum values of Br, HcB, and (BH)max.

Features of structure-sensitive hard magnetic alloy Fe – 25 wt. % Cr – 15 wt. % Co manufactured by Laser Powder Bed Fusion

It was studied the structure of alloy manufactured on the RussianSLM FACTORY unit by laser powder bed fusion. The powder was produced by gas atomization from ingots on a HERMIGA 75/3VI unit. By constructing a hesteresis loop, data were obtained that indicate an increase in the magnetic characteristics (Br, Bd, Hcb, Hcm and BHmax) in additive samples in comparison with similar ones obtained by foundry technologies.

Sputtered high perpendicular magnetic anisotropy CoPt thin film on flexible substrate at low temperature

In this study, CoPt alloy thin films with alternative sputtering of 0.4 nm-Co and 0.5 nm-Pt layers, [Co0.4/Pt0.5]n, on Pt underlayers were sputtered on rigid glass and soft PI (Polyimide) substrates at 100°C. The effects of repetition (n) of the [Co0.4/Pt0.5]n films on the magnetic properties and microstructures of [Co0.4/Pt0.5]n films were investigated. Results showed that [Co0.4/Pt0.5]4 film had a high perpendicular magnetic anisotropy (PMA (S⊥>0.98)) and a magnetocrystalline anisotropy constant (Ku∼1.12×107 erg/cm3), which were close to the properties of L11-CoPt film prepared at higher temperatures (∼300°C) as seen in previous works. Increasing repetition also increased residual stress and further reduced perpendicular magnetic properties. Thus, better magnetic properties would be obtained in the thinner case. The outstanding PMA properties of CoPt film still well kept as the rigid glass was replaced by flexible PI substrate. In this work, perpendicular magnetic CoPt film could be prepared at lower temperatures (∼100°C) on soft PI substrate. It strongly enhanced low temperature applications of hard magnetic alloy thin films, such as magnetic electronic components with high Ku and PMA on flexible substrate.

Phase Transformations and Properties of Concentration-Inhomogeneous Magnetic Materials Based on the Fe–30% Cr–27% Co System

The phase and structural transformations of a powder hard magnetic alloy of the Fe–30% Cr–27% Co–1% Si–0.07% B system with a metastable α1 + α2 phase composition, elevated cobalt content, and high level of magnetic properties are studied. The density and variation coefficient of the concentration of main elements of sintered billets at a level of deformable analogs are attained by sintering in the α phase with contact melting in the presence of a “vanishing” liquid phase formed due to the addition of silicon and boron ferroalloys. A kinetic approach to the development of a competitive hard magnetic alloy with a high fraction of a strong magnetic phase is proposed. The influence of boron additives on the incubation period of the formation of the undesirable σ phase and the temperature range of the concentration stratification of the α solid solution into the strong magnetic α1 phase and weak magnetic α2 phase are established. Optical microscopy, X-ray phase analysis, and differential scanning calorimetry are used to determine the temperature–temporal parameters of the thermal treatment of the alloy, including quenching, thermomagnetic treatment (TMT), and final aging, which provide the required combination of Hc and Br due to an increase in stability of a metastable α phase up to 20 min in a temperature range of spinodal decomposition α → α1 + α2. The largest increase in magnetic properties after TMT observed at the first and second stages of final aging is associated with the supplementary decomposition of the α solid solution and the formation of subgrain boundaries. Elements of the formed structure have submicron and nanometer sizes that correlate with the results of studying the deformable alloys based on the Fe–Cr–Co system. The anisotropic α1 + α2 structural state attained by thermomagnetic treatment provides an increase in characteristics of magnetic properties of the studied 30Kh27KSRA powder alloy to 30% and squareness ratio of the magnetic hysteresis loop of 0.82.

Effects of Sm on structural, textural and magnetic properties of Fe–28Cr–20Co–3Mo–2V–2Ti hard magnetic alloy

Present work elaborates the development of 45-xFe-28Cr–20Co–3Mo–2V–2Ti-xSm; x = 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 wt% hard magnets using traditionally induction melting and casting, isothermal magnetic annealing and multiple aging treatments. The crystal structure, magnetic phases, crystallographic texture, microstructure and magnetic characteristics of processed magnets have been systematically investigated and their results are discussed. Studies showed that magnetic characteristics of the processed magnets rely on the alloy chemistry, nature of phases, metallurgical structure and heat treatment procedure. Magnetic hardening in 45Fe–28Cr–20Co–3Mo–2V–2Ti magnet resulted from the shape magnetic anisotropy of {110}<001> textural Fe–Co–V (55.8%) and Cr–Mo–Ti (44.2%) nanoscale structures which leads to maximum (BH)max of 33.4 kJ/m3, Br of 0.71 T and Hc of 114 kA/m. The micro-addition of 2 wt% Sm to 45Fe–28Cr–20Co–3Mo–2V–2Ti alloy caused to improve magnetic characteristics as much as (BH)max of 63.2 kJ/m3, Br of 1.04 T and Hc of 148 kA/m due to conjunction of shape magnetic anisotropy of Fe–Co–V (58.2%), Cr–Mo–Ti (23.8%) phases and magnetic field anisotropy of SmCo5 (18%) phase.

Microstructure Evolution and Some Properties of Hard Magnetic FeCr30Co8 Alloy Subjected to Torsion Combined with Tension.

The hard magnetic alloy FeCr30Co8 alloy was subjected to severe plastic deformation (SPD) by torsion combined with tension in the temperature range of 750 °C to 850 °C. This range of deformation temperatures corresponds to the α solid solution on the Fe–Cr–Co phase diagram. The study of the alloy after SPD by means of X-ray diffraction (XRD) and scanning and transmission electron microscopy techniques showed the formation of a gradient microstructure with fine grain size in the surface layer and precipitation of the hard intermetallic σ-phase. Next, the magnetic and mechanical properties of the deformed alloy after short annealing at 1000 °C and magnetic treatment were studied. A slight decrease in coercive force was found, along with a significant gain in plasticity and strength. The effective deformation temperature was determined to obtain the optimal magnetic and mechanical characteristics of the alloy. This method of deformation can be applied for the improvement of the mechanical properties of some magnets (high-speed rotors) which should have good magnetic properties within their volume while maintaining good mechanical properties on the surface.

HDDR treatment of Ce-substituted Nd2Fe14B-based permanent magnet alloys - phase structure evolution, intergranular processes and magnetic property development

Aiming for cost-efficiency through balanced utilization of rare-earth resources, the use of Ce, the cheapest and most abundant of all rare-earth elements, as potential candidate to substitute the expensive and resource-critical Nd in Nd2Fe14B hard magnetic alloys was tested in this work. Emphasis is put on the effects of substitution on the alloys structural properties and the related response to hydrogen treatment, one of the main processing routes in the production of Nd2Fe14B-based permanent magnets. The study follows the influence of Ce substitution on the phase structure and magnetic property development in hydrogen decrepitated and HDDR processed (Nd1-xCex)15Fe79B6 (x = 0, 0.1, …, 0.6) strip-cast alloys. Intergranular CeFe2 segregates in the as-cast alloys from x = 0.3, increases in proportion with x at the expense of the hard magnetic phase and replaces the rare-earth-rich grain boundary phase. Upon hydrogen absorption, CeFe2 transforms in amorphous CeFe2Hx which further decomposes into CeHx and α-Fe. The rare-earth components from CeHx and the rare-earth-rich hydrogenated phase melt upon hydrogen desorption, enabling the redistribution of the intergranular material among the Nd2Fe14B grains upon the desorption and recombination stage of the HDDR treatment, thus facilitating grain decoupling and coercivity development. Within a generally decreasing trend, at x = 0.2 and 0.3 Ce ratios, coercivity (μ0HC) and remanence (Br) of the HDDR powders remained rather stable despite the segregation of CeFe2 phase occurring at x = 0.3. Significant texture and very reasonable magnetic properties were obtained at x = 0.3 (μ0HC = 1.05 T and Br = 0.88 T), attributed to a favorable phase composition with Ce mainly concentrated in the intergranular material.

Effect of a high magnetic field on hard magnetic multilayered Fe-Pt alloys

Abstract Fe-50 vol%Pt multilayers that were prepared by accumulative roll-bonding were annealed in vacuum for 2 h at various temperatures between 723 K and 823 K. Some samples were annealed without any high magnetic field (HMF). Others were subjected HMF up to 31.2 T, applied in either in-plane or out-of-plane directions. The annealing partially transformed the original multilayered structure into a polycrystalline hard-magnetic FePt magnetic phase with ordered L10 structure. Textured FePt/Fe nanocomposite foils were formed under HMF. Magnetic anisotropic behavior was observed in the annealed FePt/Fe composite because of the textured nanostructure. HMF annealing decreased grain size and increased the (0 0 1) texture along the HMF direction. In the sample annealed with out-of-plane HMF, both coercivity and maximum energy product were enhanced because of higher (0 0 1) out-of-plane texture and finer nanoscaled grain sizes compared to other samples. An in-plane HMF appeared to strongly inhibit phase transformation. This inhibition likely resulted from a change in Gibbs free energy and the diffusion inhibition caused by HMF.

Magnetic Properties of Hard Magnetic Powder Alloy Fe – 27% Cr – 10% Co (27Kh10KA)

Magnetic hysteresis properties (residual induction Br, coercivity Hc and maximum energy product (BH )max) of Fe – 27% Cr – 10% Co (27Kh10KA) hard magnetic powder alloy are assessed after different heat treatments. Optimum modes of heat treatment are determined using TRM251 programmed derivative-proportional-integral controllers. The magnetic characteristics of the specimens exceed those of the widely used alloy 25Kh15KYuBF with a higher cobalt content. The prospects of the Fe – 27% Cr – 10% Co (27Kh10KA) powder alloy for commercial production are considered.

Noncollinear spin structure in Fe3+xCo3−xTi2 ( x=0,2,3 ) from neutron diffraction

Neutron powder diffraction has been used to investigate the spin structure of the hard-magnetic alloy $\mathrm{F}{\mathrm{e}}_{3+x}\mathrm{C}{\mathrm{o}}_{3\ensuremath{-}x}\mathrm{T}{\mathrm{i}}_{2}$ ($x=0,2,3$). The materials are produced by rapid quenching from the melt, they possess a hexagonal crystal structure, and they are nanocrystalline with crystallite sizes $D$ of the order of 40 nm. Projections of the magnetic moment onto both the crystalline $c$ axis and the basal plane were observed. The corresponding misalignment angle exhibits a nonlinear decrease with $x$, which we explain as a micromagnetic effect caused by Fe-Co site disorder. The underlying physics is a special kind of random-anisotropy magnetism that leads to the prediction of $1/{D}^{1/4}$ power-law dependence of the misalignment angle on the crystallite size.