Residual Induction Br Research Articles

INVESTIGATION OF MAGNETIC HYSTERESIS PROPERTIES OF ISOTROPIC MAGNETICALLY HARD ALLOYS OF THE Fe-Cr-Co SYSTEM ALLOYED WITH TUNGSTEN

Hard magnetic alloys Fe-30Cr-20Co (wt.%) alloyed with tungsten in an amount of up to 3 wt.% were obtained by powder metallurgy. A study of magnetic properties showed that tungsten additions increase the values of the coercivity Hc and the maximum energy product (BH)max, but at the same time reduce the residual induction Br. This effect increases with increasing tungsten content in the material. The maximum values of Hc (55.8 kA/m) and (BH)max (17.2 kJ/m3) are observed in the alloy alloyed with 3 wt.% W. At the same time, the alloys studied in the work turned out to be sensitive to thermal conditions processing. According to X-ray phase analysis, after a full processing cycle, alloys contain a noticeable proportion of non-magnetic ɣ-phase, but the magnetic properties correspond to the level of cast analogues. During compression tests, all samples of tungsten alloyed alloys failed before reaching a deformation rate of 20%, while the unalloyed Fe-30Cr-20Co (wt.%) alloy deformed without failure under these conditions. Thus, tungsten additives reduce the ductility of the material.

Effect of Heat Treatment on the Magnetic Hysteretic Properties of an Anisotropic Hard Magnetic Fe–28Cr–10Co–0.5W Powder Alloy

Abstract—The magnetic hysteretic properties (residual induction Br, coercive force HcB, maximum energy product (BH)max) of an anisotropic hard magnetic Fe–28Cr–10Co–0.5W powder alloy are estimated after heat treatment under the conditions chosen by the Statgraphics XVI Centurion software. The magnetic hysteretic properties (Br = 1.336 T, HcB = 46.1 kA/m, (BH)max = 44.1 kJ/m3) reached after the optimum heat treatment exceed the analogous properties of one of the main industrial alloys, namely, 25Kh15KYuBF (State Standard GOST 24897–81), by more than 15%; in this case, the cobalt content in the alloy under study is one third less than that in the industrial alloy. Because of this, the hard magnetic Fe–28Cr–10Co–0.5W powder alloy can be recommended for industrial development.

Electro-discharge sintering of nanocrystalline NdFeB magnets: process parameters, microstructure, and the resulting magnetic properties

This study investigates the compaction of nanocrystalline NdFeB magnet powder by electro-discharge sintering (EDS). On this account, process parameters, microstructure, and the associated magnetic properties of the EDS-densified nanocrystalline NdFeB specimens were investigated by varying the discharge energy EEDS and compression load pEDS. Although optimized process parameters could be evaluated, three different microstructures (fully densified zone, insufficiently densified zone, and melted zone) are present in the EDS-compacted specimens. Thereby, volume fractions of these formed three different microstructures determine the resulting mechanical and magnetic properties of the specimens. For all specimens, the intrinsic coercivity Hc,J deteriorates with increasing discharge energy, as the generated Joule heat leads to microstructural changes (grain growth, dissolution of magnetic phases), which reduces the magnetic properties. The compression load has less influence on the coercivity Hc,J, as it only affects the initial resistance of the pre-compacted powder loose. The residual induction Br deteriorates with increasing the discharge energy due to microstructural changes. An increase in the compression load pEDS results in an increase in the specimens’ density and thus promotes the residual induction Br.

Method for permanent magnet undulator parameter stabilizing against temperature variation

Stability of undulator parameter (Kund) is very important for operation of synchrotron radiation sources. Because Kund defines radiation harmonics energies, its variation causes drift of harmonic energies and undesirable photon flux change during data collection.Very often, the origin of Kund drift is temperature change. To stabilize Kund, the temperature of the undulator and ambient should be kept constant with ∼±0.1 °C or better precision. Although keeping the temperature constant in a large space with such precision is a challenge, it can be done with adequate resources. However, the time needed to reach operating temperature with required precision after interruption of standard operation can be quite long. Observation made at Cornell High Energy Synchrotron Source (CHESS) indicated that this time can be ∼12 h or longer. During this time period, Kund of undulator magnets is drifting, causing variation of photon flux. This compromises beam line operation. Reducing the sensitivity of Kund to temperature variation would be beneficial.In this paper, we developed the concept of stabilizing of Kund against temperature change utilizing the effect of differential thermo-expansion. According to the concept, girders should include specific parts made of materials with different coefficients of thermo-expansion (CTE). When temperature changes, it will create the desired deformation which can compensate for the change in magnetic field caused by temperature sensitivity of permanent magnet residual induction Br. Engineering FEM modeling and analysis of the magnetic field of the specific girder design reveal feasibility and practicality of the concept.In the paper we present results of the engineering modeling, magnetic field analysis, and supporting experimental data.

A comparative study of BaxSr1−xFe12O19 ferrite permanent magnets prepared by ball milling and sol–gel routes

Given the huge and increasing global demand for permanent magnet supply, even slight improvements of the magnetic properties and cost effectiveness of permanent magnet materials could incur huge energy and money savings. This article is concerned with the optimization of the experimental conditions for the production of pure M-type BaxSr1−xFe12O19 hexaferrites with improved magnetic properties. X-ray diffraction analysis revealed the formation of a single M-type hexaferrite in the ball milling route at a sintering temperature of 1100 °C for the samples with x = 0.0 and 0.5, and at 1200 °C for x = 1.0. In the sol–gel route, however, a single M-type phase was successfully synthesized at a significantly lower temperature of 890 °C. The magnetic parameters of the samples prepared by ball milling exhibited an improvement at lower Ba contents. On the other hand, the samples prepared by sol–gel method exhibited a significant improvement of the intrinsic coercivity (HcM) compared with those prepared by ball milling, with the highest value of 5.9 kOe observed at x= 0.0 and sintering temperature of 1000 °C. The saturation and remnant magnetization, however, were not influenced significantly by the synthesis route, and remained relatively high, comparable with the best parameters for ferrite isotropic magnets. The sample with x = 1.0 prepared by sol–gel method and sintering at 890 °C exhibited the highest residual induction Br = 2509 G, practical coercivity HcB = 1919 Oe, and maximum energy product (BH)max = 9.9 kJ m−3.

Problems of Development of Mim Technology in Russia as Applied to Production of Permanent Magnets

Main problems arising in installation of novel processes of production of permanent magnets based on the Fe – Cr – Co and Sm – Co systems are presented. The technological possibilities of production of permanent magnets from an alloy of the Fe – Cr – Co system by methods of MIM technology and powder metallurgy are described. Methods of MIM-technology with the use of domestic granulate are used to fabricate permanent magnets based on alloy 25Kh15KA (Fe – Co – Cr system) with residual induction Br = 1.12 T, maximum energy product (BH)max = 23.0 kJ/m3 and coercivity HcB = 39.7 kA/m.

Synthesis of Hard-Magnetic Material of the Fe–Cr–Co System Made of a Spherical Powder

Abstract—A short-cut method of synthesis of a hard-magnetic material made of a spherical powder of the 25Cr–15Co–Al–Nb alloy obtained by spraying a melt with a stream of gas was proposed. It was established experimentally that uniaxial pressing of the powder in the initial state did not allow obtaining compacts without defects despite of the split die and pressing pressure up to 600 MPa. Application of powder annealing in hydrogen at 800°C decreases the hardness of the material particles. However, when compacting, the similar separation of compacts is observed as with the original powder. The use of a plasticizer gives a positive effect for improved compactibility, but it reduces the values of magnetic hysteresis characteristics. It is shown that the mechanical activation of spherical powder in a planetary mill allows obtaining the high-quality compacts and sintered specimens with high values of magnetic characteristics. The changes in the morphology of the powder particles during processing are revealed. Enlargement of powders due to cold welding is observed; the shape of particles changes dramatically as compared to the original powder. The particles size spread is substantially smaller in comparison with the original spheres; a heteraxial character is observed. Application of balls of larger diameter for grinding leads to better results. The magnetic hysteresis characteristics of hard-magnetic material synthesized from an alloy powder mechanically activated for 80 min are at a high level which ensures its technical application: residual induction Br = 1.18 T; coercive force НсВ = 43.1 kA/m; maximum magnetic product (ВН)max = 31.8 kJ/m3.

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.

Magnetic Characteristics of Sintered (Pr,Dy)–(Fe,Co,Cu)–B Materials with Various Copper Contents as Functions of the Annealing Temperature

The effect of copper alloying on the coercive force and the residual induction of sintered materials (Pr0.53Dy0.47)13(Fe0.64Co0.36)resCuxB6 (x = 0–3 at %) annealed at various temperatures is considered. The dependences of coercive force HcI and residual induction Br on the copper content are found to be nonmonotonic. This fact is explained by that alloying with copper leads to a change in the phase composition, which is accompanied by an increase in the coercive force and the residual magnetization of the alloy, while a change in the chemical composition and the thickness of intergranular interlayers upon copper alloying leads to a decrease in the values of HcI and Br as the copper content increases.

Influence of heat treatment on the magnetic properties of Fe-28%Cr-7%Co-2%Mo-0.5%Si powder hard magnetic alloy

The hard magnetic alloy Fe-28%Cr-7%Co-2%Mo-0.5%Si (in wt. %) was prepared by the methods of powder metallurgy. The maximum magnetic properties on the alloy was received after the TMT temperature of 540 °C and was the following: residual induction Br up to 1.3 T, coercive force Hc up to 40 kAm−1 and maximum energy product (BH)max up to 31 kJm−3. The hardness of the alloy increases from 228 to 250 HV 30 in the temperature range of spinodal decomposition at 600 – 660 °C. The coefficient of thermal expansion of the alloy is 13,1*10−6 K−1. It was found that the additional annealing of the alloy till 460 °C can increase the coercive force approximately for 6 kAm−1.

Magnetic Hysteretic Properties of a Powdered Fe–27Cr–10Co–1Mo Hard Magnetic Alloy

The magnetic hysteretic properties of an Fe–27Cr–10Co–1Mo (27Kh10K1M) magnetic hard alloy are studied. Residual induction Br (up to 1.36 T), coercive force HcB (up to 45.4 kA/m), and maximum energy product (BH)max (up to 44 kJ/m3) have been evaluated using the Statgraphics Centurion XVI software package after optimum heat treatment. The obtained data are higher than those of a commercial iron–chromium–cobalt 25Kh15KA alloy (Russian Standard GOST 24897–81) by 15–20% on average. Different optimum heat treatment of the alloy is shown to be required to obtain the optimum values of its residual induction Br, coercive force HcB, and maximum energy product (BH)max.

Densification of nanocrystalline NdFeB magnets processed by electro-discharge sintering – Microstructure, magnetic, and mechanical properties

This work investigates the densification process of nanocrystalline NdFeB powder by electro-discharge sintering (EDS) and the associated magnetic properties. The EDS technique is used as a fast and energy-saving compaction process for metal powders. A large current is discharged from capacitors into a pre-compacted loose powder, thus resulting in complete compaction. In this study, the microstructure, magnetic, and mechanical properties of the compacted, hard magnetic NdFeB specimens were investigated under variation of the energy EEDS and compression load pEDS. For all specimens, the intrinsic coercivity HcJ decreases on increasing the discharge energy. However, the compaction load has apparently no influence on the coercivity HcJ, whereas the residual induction Br decreases only with increasing discharge energy. An increase in the compression load pEDS causes an increase in the specimens’ density and thus promotes residual induction Br. The applied EDS parameters led to the formation of three different microstructures (insufficiently densified zone, fully densified zone, and remelted zone) along the cross-section of the EDS-densified specimens. Volume fractions of the three different microstructures that form during the EDS process determine the resulting mechanical and magnetic properties of the specimens.

Low-temperature magnetic properties of NiCrxFe2–xO4 ferrites

Nickel-chrome ferrites of general formula NiCrxFe2–xO4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) were produced using low-temperature sol-gel self-combustion technique. Magnetic hysteresis loop of the samples showed that due to a low coercive field Hc, in the range of 2484–4283 A/m at 77 K, the ferrites are soft magnetic materials. The residual induction Br of the magnetic field decreases with increasing the concentration of Cr3+ ions due to a weakening of the interaction between the tetrahedral and octahedral sublattices of the ferrite with the spinel structure. The specific saturation magnetization σs of NiFe2O4 ferrite is 33.9 A m2/kg. The blocking temperature Tb was determined; its average value was found to be 157 K.

Effect of gadolinium on the properties of Pr–Dy–Fe–Co–B materials

Sintered (Pr1–x–yDyxGdy)13–14(Fe1–zCoz)balB6–7 materials (x = 0.18–0.58, y = 0.05–0.33, z = 0.2–0.36) have been studied. The magnetic moments of gadolinium ions and those of the sublattice formed by Fe and Co ions are shown to be ordered antiferromagnetically. It is noted that an increase in the content of gadolinium, which substitutes for dysprosium, leads to an increase in residual induction Br, a decrease in coercive force HcJ, and an increase in the absolute value of the temperature coefficient of induction. The opposite effect takes place in the case of substitution of gadolinium for praseodymium in materials with a fixed dysprosium content.

Magnetic and structural properties of spark plasma sintered nanocrystalline NdFeB-powders

Near-stoichiometric NdFeB melt-spun ribbons have been subjected to spark plasma sintering varying the process temperature TSPS and pressure pSPS between 600 and 800°C and 50–300MPa, respectively. Produced bulk magnets were analyzed regarding microstructure and magnetic properties. For all samples the intrinsic coercivity Hc,J gradually decreases with increasing sintering temperature and pressure, while residual induction Br increases simultaneously with sample density. Densities close to the theoretical limit were achieved for pSPS≥90MPa and TSPS≥650°C. With increasing TSPS precipitations of Nd-rich and Fe-rich phases have been observed as a result of a decomposition of the hard magnetic Nd2Fe14B phase. Under optimum sintering conditions of pSPS=300MPa and TSPS=650°C high-density bulk magnets with Hc,J=652kA/m, Br=0.86T and (BH)max=106kJ/m3 have been produced.

Magnetic methods for estimation of load and damage levels in X70 steel

The paper studies the magnetic, mechanical and structural characteristics of X70 steel after controlled rolling. The coercive force Hc, residual induction Br, maximum permeability μmax and maximum permeability field Hμmax measured in situ in the loaded or unloading steel magnetized in different directions about the pipe axis are analyzed for applicability as parameters from which the working tensile stress in a pipeline and its preceding overload with attendant transition to the plastic range can be determined. An approach is proposed for estimating the accumulated damage level in the steel under tension or torsion from the coercive force Hc and/or saturation magnetization Jmax.

Hydrogen as a working atmosphere for manufacturing permanent magnets based on rare-earth metals

The phase compositions and magnetic properties of permanents magnets of the systems Sm – Co and Nd – Fe – B are analyzed. Features of the hydrogenation–disproportionation–desorption– recombination (HDDR) process in the Nd 2 Fe 14 B intermetallic are considered. Using the Dd – Fe – B system as an example, we assess stages of manufacture of commercial permanent magnets and show the prospect of using hydrogen as a working atmosphere for the manufacture of magnetic powder. It is established that the HDDR of Dd – Fe – B alloys leads to their homogenization, grain refinement to a grain size of 0.2 to 0.5 μm, and an increase in the volume content of the main ferromagnetic phase Dd 2 Fe 14 B. By optimizing such a treatment, we managed to increase the magnetic energy (by 10%) and the lift force (by 25 – 27%) of Dd – Fe – B commercial permanent magnets. In modern materials science, a new trend in chemicothermal treatment of metals that consists of using hydrogen as a working atmosphere is being intensively developed. Developed hydrogen technologies are based on the regularities of its effect on the phase transformations, specifically, atomic ordering and hydride formation, in metals [1 – 3]. Earlier, magnetic materials were treated in a hydrogen atmosphere to clear them from impurities by annealing at high temperatures (1100 – 1300°C) [4]. However, in the manufacture of permanent magnets based on rare-earth metals (REMs), the possibility of using hydrogen both during their milling (hydride embrittlement) and for the change of the phase–structural state arose. Optimizing conditions for such a treatment, one can increase the operating characteristics of magnets (the coercive force Hc and residual induction Br ) and decrease the consumption of energy in their manufacture. Rare-earth magnets based on samarium were first obtained in the early 1970s. Alloys of the samarium–cobalt (Sm – Co) system have high saturation magnetization, coercive force, heat resistance, and corrosion resistance. However, due to the high cost, their use in industry is limited to a range of elevated temperatures (150 – 500°C). At present, magnets based on the Nd – Fe – B system are most extensively used. Of all known ferromagnets they exhibit the highest value of the energy product ( BH ) max (to 50 MG ⋅ Oe), which is five times higher than those of the best Alnico type magnets (Al – Ni – Co) [4]. Moreover, the determining advantage of these magnets over other materials is the relatively low cost calculated per unit magnetic energy (Table 1).

Highly Anisotropic Powders of Alloys of Nd - Fe - B System with Magnetic Energy of Up to 27 MG · Oe Obtained by the Method of Hydrogenation-Dehydrogenation

The effect of additives of Nb, Ga, Co, Zr, Al, and Dy and of the temperature of hydrogen treatment on magnetic properties of powders of alloys based on the Nd2Fe14B compound and fabricated by the method of cyclic hydrogenation-dehydrogenation is investigated. Powders of an alloy with additives of Nb, Ga, and Dy fabricated in an optimum mode have maximum magnetic energy of 27 MG · Oe (216 kJ/m3). Plastomagnets from these powders with an epoxy binder have magnetic energy of 16 MG · Oe (128 kJ/m3) at residual induction B r = 8.35 kG, J H c = 14 kOe, and B H c = 7 kOe.

Optimization of the Mode of Isothermal Thermomagnetic Treatment of Magnetically Hard Alloy of the Fe – Cr – Co System with 8% Co

The magnetic properties of deformable magnetically hard alloy Fe – 27.5% Cr – 7.9% Co – 0.3% V – 0.65% Si – 0.4% Ti are studied after isothermal thermomagnetic treatment (ITMT) optimized using the method of experimental design. Mean values of residual induction Br, coercive forces Hci (with respect to induction) and Hcm (with respect to magnetization), and maximum energy product (BH)max after optimum ITMT are determined. A three-dimensional dependence of the coercive force Hcm on the temperature and time of the ITMT is plotted.

Preparation of barium hexaferrite by a hydrothermal method: structure and magnetic properties

Barium hexaferrite, BaFe12O19, was obtained in hydrothermal conditions from a water suspension of α-FeOOH and Ba(OH)2 · 8H2O at a temperature about 315° C. X-ray and Mossbauer spectroscopy as well as electron microscopy investigations demonstrated the appearance of α-Fe2O3 as an intermediate phase in the hydrothermal process. The magnetic characteristics of the obtained isotropic magnets are the following: coercive fieldH c ∼159 kA m−1, residual inductionB r ∼0.26 T, maximum energy product (BH) max∼12 kJ m−3. The hydrothermal procedure for the preparation of barium hexaferrite in comparison with the conventional one is discussed.