Search

This work presents unique microstructure and thermal properties of the Fe55Ni20Cu5P10Si5B5 alloy produced by novel modification of the melt-spinning method, where two precursor alloys are simultane...

An elemental powder mixture of Fe-50 at.%Al with addition of 30 vol% of B was subjected to mechanical alloying (MA). Phase transformations occurring in the material throughout MA were investigated by Mossbauer spectroscopy. Examination of thermal behaviour of the MA product by differential thermal analysis revealed four exothermic peaks. Structural and phase transformations induced in the MA powders by heating in a calorimeter up to 530, 630, 730 and 1000 °C were investigated by X-ray diffraction and Mossbauer spectroscopy. The powders containing 30% of B in the as-milled state and after heating up to 1000 °C were examined by scanning electron microscopy. Magnetic properties of the MA product before and after heating up to 1000 °C were investigated. It was found that MA of the (Fe-Al)-30 vol%B powders resulted in the formation of a composite structure with boron particles embedded in the predominantly amorphous Fe-Al-B matrix. Additional Mossbauer measurements performed on MA products with a smaller boron content of 5, 10 and 20 vol% evidenced the crucial role of boron addition in promoting the formation of Fe-Al-B amorphous phase by MA process. The structure of the (Fe-Al)-30 vol%B powders after their controlled heating comprised of fine B particles distributed in the two-phase matrix of nanocrystalline (FeAl or AlFe2B2-type) and amorphous phases or in the nanocrystalline matrix (AlFe2B2 + Al13Fe4), depending on the temperature up to which the material was heated. To the best of our knowledge, the nanocrystalline AlFe2B2 phase was obtained for the first time by mechanical alloying followed by heat treatment.

The paper presents a new approach to selective laser melting (SLM) of alloys with low glass-forming ability and the basics of microstructure evolution during SLM of iron-based metallic glasses. After extensive parameters optimization, a novel scanning strategy, involving two-step melting, comprising preliminary laser melting, followed by short-pulse amorphization, has been introduced to maximize the glassy phase fraction and ensure good magnetic properties. Single melted samples show poor amorphization with well separated amorphous regions and coercivity of 1032 A/m. Second melting increased the glassy phase content by over an order of magnitude - up to 89.6% and reduced coercive force over four-times to 238 A/m. X-ray diffractions show significant difference between, arising from melt, disordered Fe(Si) phase and devitrified, ordered Fe3Si. Coexistence of those phases has been shown in heat affected zone by electron diffraction. Beneficial effect of the novel remelting strategy has been explained on the basis of restricted crystallization in heat-affected zone and reduction of sample overheating, by application of the Point-Random strategy.

Soft magnetic composites (SMCs) are usually prepared from microcrystalline Fe, Fe-Si or Fe-Si-Al powders. Other powders, including nanocrystalline ones, are relatively rarely used. The objective of this work was to prepare SMCs from milled Fe-Si-B-Nb-Cu nanocrystalline ribbon and study their magnetic properties. These SMC cores exhibited very low coercivity and, despite no synthetic oxide layer, relatively high resistivity. A combination of these properties resulted in exceptionally low core loss at low frequency and in some initial tests at higher frequencies. Moreover, the influence of powder size fraction on the magnetic properties was also investigated, leading to a conclusion that the use of coarser particles resulted in higher permeability. Further increase in permeability was achieved by mixing the coarsest powder size fraction with the finest one. The presented results show a promising future for this kind of materials.

Crystalline-amorphous matrix composites preserve the amorphous material high strength and additionally gains on plasticity. Substituting hard crystalline precipitates with soft ones should even more improve the latter. Therefore, this work was aimed at verifying, whether Ag and Ni-Si-B alloy shows liquid immiscibility and consequently, if they might form crystalline Ag/Ni-Si-B amorphous/crystalline composite. Firstly, a mixture of 95 wt% of Ni-Si-B (1559-40) and 5 wt% of Ag powders was arc-melted in argon and cooled at copper plate. The solidification process was documented by IR mid-wave camera and Time/Temperature graph. The microstructure of the ingot was studied using a scanning electron microscope (SEM) and light microscope (LM). Secondly, the powders mixture was plasma sprayed on a cooled copper plate. The cross-section microstructure and the phase composition of the plasma spray deposit were analyzed with a transmission electron microscope (TEM), scanning electron microscope (SEM) and X-ray diffractometer (XRD). The thermal characteristics of the plasma sprayed deposit and the Ni-Si-B powder were analyzed using differential thermal analysis (DTA) and compared. The results show that the melted Ag and Ni-Si-B powders form immiscible liquids at high temperatures used both during arc-melting and plasma-spraying. The proved that that the plasma spraying enables production of a Ni-Si-B/Ag composite with high strength Ni-based matrix with dispersed in it fine soft Ag-FCC flake-like particles.

Nanocrystalline Fe80-x-yCoxNiyCu1Nb3Si4B12 alloys were prepared by the annealing of amorphous ribbons. Primary crystallization of the alloys annealed at temperatures of between 500 and 550°C was studied by X-ray diffraction and Mössbauer spectroscopy. Magnetic properties of the alloys were investigated using a hysteresis loop tracer and vibrating sample magnetometer. The annealed ribbons are composed of a two-phase nanostructure consisting of bcc Fe-based grains embedded in an amorphous matrix. Conversion electron Mössbauer spectroscopy (CEMS) measurements reveal a more advanced crystallization process in the surface layers when compared with the volume of the ribbons. The degree of saturation magnetization of the nanocrystalline alloys is of about 1.5 T. The coercive field varies from 1.0 to 6.5 A/m and peaks at an annealing temperature of 525°C. Magnetic softening of the nanocrystalline alloys observed after annealing at 550°C is correlated with a volume fraction of the nanocrystalline bcc phase.

Cryogenic thermal cycling (CTC, between room temperature and 77 K) of a (Cu,Zr)-based bulk metallic glass (MG) leads to substantial reductions in the initial yield load Fy observed on instrumented indentation, and can reverse annealing-induced increases in Fy. In contrast, for hardness and elastic modulus, CTC has much less effect and can only partially reverse annealing effects. The distribution of Fy values is wide, reflecting heterogeneity in the MG. For a melt-spun Fe-based glass, CTC with more cycles induces similar changes in Fy, and has almost no effect on the magnetic properties. Such differing effects of CTC can be consistently interpreted in terms of its preferential effect on soft spots in a relatively rigid glass matrix. The capability for targeted stimulation of shear-transformation zones permits tailoring of MG properties, clearly facilitates initiation of plastic flow, and offers the prospect of improved plasticity and toughness even in annealed samples.

Results concerning the influence of deposition conditions (effective power, P eff , pulse length, τ , and working gas pressure, p ) as well as of thermal treatments on the properties of Fe 73.5 Cu 1 Nb 3 Si 15.5 B 7 thin films, deposited by high power impulse magnetron sputtering (HiPIMS) technique, are presented. The P eff , τ and p values were varied in the range of 30–90 W, 4–20 μs and 8–60 mTorr respectively. According to the XRD analysis, in as-deposited state, all the prepared samples are amorphous. For P eff constant the coercive magnetic field, H c , increases whit τ , while for τ constant H c decreases when P eff increases. The lowest H c values have been obtained after the samples were annealed at temperatures between 450 °C and 480 °C, when the average size of the α-Fe(Si) grains and the crystalline volume fraction increase about 45% and 20% respectively.

Studies of rapidly solidified Pr9−xDyxFe60Co13Zr1+yTi3−yB14 (where x = 0, 1 and y = 0, 1) thick ribbons, 1 mm diameter (dia.) rods and 3 mm outer diameter (o.d.) tubes show good hard magnetic properties in as-cast state. Change of Ti to Zr ratio results in variation of the glass forming abilities that has significant impact on magnetic properties. Low temperature annealing at 573 K/10 min of the Pr9Fe60Co13Zr1Ti3B14 alloy samples resulted in an improvement of their coercivity field. The X-ray diffractometry and Mossbauer spectroscopy allowed determining the volume fractions of constituent phases formed during rapid quenching.

The reflection and absorption properties of powdered nanocrystalline FeSiBCuNb (“Finemet”) alloy at microwaves have been presented. To visualize the shielding ability of this material, the complex permittivity and permeability of pulverized Finemet in the frequency range from 0.2 to 10 GHz have been studied. To measure the permittivity and permeability of powdered Finemet, the modification of the Nicolson, Ross, and Weir method was presented. The modification of this method was mainly based on the unwrapping technique of the measured S-parameter phases. The investigation of permittivity and permeability was realized for pure powders. Four groups of powders with different particle sizes below 200 μm have been investigated. To assess the shielding effectiveness of the nanocrystalline Finemet, two attempts were analyzed. The investigation of the reflection loss of material layer with metal sheet attached to the backside as a reflector was investigated. On the other hand, the reflection and absorption factors of 3-mm-thick layer in free space were additionally analyzed. The obtained results show that the pulverized nanocrystalline Finemet alloy with particle size below 25 μm possesses good absorption properties and, for such particles, the absorption factor is significantly higher than the reflection factor.

Iron-based bulk metallic glasses have been known for several attractive properties, such as high mechanical strength and magnetic softness. They also exhibit sensitivity of magnetic properties to stress, which is the result of magnetoelastic coupling. In this paper, these combined features were exploited to build a simple, but effective magnetoelastic force sensor. It was found that when rods made of glassy (Fe,Co,Ni)-Nb-Si-B alloys, used as cores in a transformer, are subjected to compressive stress, voltage on secondary winding changes with the application of force. When proper measurement conditions are met, the dependence of output voltage versus force is nearly linear. Furthermore, rods with 2 mm in diameter are able to withstand forces reaching 8 kN, which gives an opportunity to design small-sized, high-load magnetoelastic force sensors.

Structure as well as magnetic and magnetoelastic properties of nanocrystalline (Fe,Co)-(Hf,Zr)-Cu-B alloys (HITPERM-type) were investigated in order to find out which factors are responsible for the magnetic hardening of these magnetically soft materials. Magnetoelastic anisotropy, caused by the presence of cobalt, was found to play the predominant role in the observed increase of coercive field. On this basis, guidelines on chemical composition and crystallisation process selection were suggested for two fields of application: soft magnetic cores and sensors or actuators cores.

Hysteresis loops of nanocrystalline samples of Fe 39 Co 39 Nb 6 B 16 − y Cu y ( y = 0, 1) HITPERM-type alloys were measured from room temperature up to 773K. The alloy with Cu shows a nearly constant value of coercivity (∼ 135A/m) in all the studied temperature range, whereas for the Cu-free alloy, the coercivity increases from 125A/m at 300K up to 190A/m at 773K. Room temperature Mossbauer spectra can be interpreted on the basis of the presence of three different regions: amorphous, crystalline and interface. The observed nanocrystalline microstructure is similar for the two alloys, although bigger crystallites are found in the alloy without Cu. The very small grain size ensures the averaging out of the magnetocrystalline anisotropy but, as the expected value of magnetostriction constant for the crystalline phase is ∼ 60ppm, the magnetoelastic anisotropy cannot be neglected.

As-quenched and nanocrystalline HITPERM-type (Fe1−xCox)86Hf7B6Cu1 alloys were investigated by conventional Mossbauer spectroscopy. The spectrum of as-quenched alloy presents a typical broadened and overlapped sextet, which confirms that the as-quenched alloy in fully amorphous state. After nanocrystallization, each spectrum of the alloys studied consists of three components: crystalline phase, interface and residual amorphous matrix except x = 0.8 alloy. Co addition increases the hyperfine field and the maximum value exhibits in the x = 0.2 alloy. The Fe concentration in bcc-FeCo crystals and the fraction of crystalline phase influenced by Co addition are opposite. The forming of boride phases after prolonged annealing decline the soft magnetic properties of the alloy studied.

It is known that Hf addition reduces the coercivity of nanocrystalline soft magnetic alloys more effectively than Zr and Nb as the inhibitor of grains growth. In this paper, the differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM) were used to evaluate the influence of Co content on the crystallization process, soft magnetic properties and structure of (Fe 1− x Co x ) 86 Hf 7 B 6 Cu 1 ( x =0–1) alloys. The coercivity was determined from the quasi-static hysteresis loop measured at room temperature and high temperatures. The Fe-containing alloys studied exhibit typical two-phase structure of nanocrystals embedded in an amorphous matrix with high crystalline volume fraction after the primary crystallization. The moderate Co addition enhances the saturation magnetization, but the coercivity also increases with Co addition. Among the alloys studied, the x =0.4 and 0.5 alloys exhibit both the low coercivity with good thermal stability and large saturation magnetization at high temperatures, which are excellent candidates for the high temperature applications in temperature range from 500 to 550 °C.

The crystallization process, structure and high temperature magnetic properties of (Fe 0.6 Co 0.4 ) 86 Hf 7 B 6 Cu 1 alloy have been investigated. The alloy after annealing at 550 °C for 1 h exhibits the good soft magnetic properties with both small local coercivity and large magnetization. Furthermore, the coercivity measured at heating temperature point of this nanocrystalline alloy holds the value below 40 A/m until the onset of secondary crystallization corresponding to the formation of high coercivity phases. Nanocrystalline (Fe 0.6 Co 0.4 ) 86 Hf 7 B 6 Cu 1 alloy is one of the excellent candidates for soft magnetic materials used at high temperature applications with the range of 500–550 °C.

The relationship between coercivity and structure in nanocrystalline (Fe1-xCox)(86)Hf7B6Cu1 (x = 0-1) alloys was surveyed. It was found that the increase of Co content in the alloys studied was accompanied by the increase of coercivity. However, we suggest that the factors influencing the coercivity change with the concentration of cobalt in these nanocrystalline alloys. In the iron-rich alloys, the average grain size and magnetostriction play predominant roles in the coercivity. On the other hand, in the case of cobalt-rich alloys, the coercivity mostly originates from the FCC-Co phase with large magnetocrystalline anisotropy and the weak exchange coupling between BCC-Fe(Co) and FCC-Co(Fe). (c) 2005 Elsevier B.V. All rights reserved.

The newest class of magnetically soft materials are the nanocrystalline iron alloys obtained by partial crystallisation of metallic glasses. Within this group, FINEMET (Fe–Si–Nb–Cu–B) and NANOPERM (Fe–Zr–Cu–B) alloys exhibit the unique combination of interesting magnetic properties. These materials may be used at temperature below 230 °C. For high-temperature applications, the HITPERM alloys (Fe–Co–Zr–Cu–B) are used. Their optimisation should lead to good (i) magnetic properties at working temperature and (ii) thermal stability of structure and properties. The alloys’ properties are the function of chemical composition and heat treatment. This work is related to the optimisation of heat treatment conditions of HITPERM alloys. High operating temperature may induce further crystallisation of amorphous matrix. It is suggested that the nanocrystallisation temperature should be as high as possible, and the optimisation of HITPERM-type alloys should focus on their chemical composition.

(Fe1−xCox)86Hf7B6Cu1 ( x = 0 – 1 ) alloys were investigated as candidates for soft magnetic materials for elevated temperature applications. The lattice parameter of nanoscale precipitate decreases with the increasing of Co content because of the large Co solubility in the α ( α ′ ) -Fe(Co) solid solution. However, it is a little larger than that of the crystalline phase in the Fe(Co) binary alloy. The Curie temperature of amorphous alloys studied monotonously increases with the increase of Co content. The nanocrystallized alloy with Co content of x = 0.4 exhibits both the higher magnetization and lower coercivity at the elevated temperature, being the optimum alloy among the alloys studied for high temperature applications.

The investigation presented in this paper was carried out on ribbon ring samples annealed for 1 hour at various temperatures (T a = 410, 440, 470, 500 and 580 °C) in order to achieve different stages of nanocrystallization and different magnetic properties. To achieve the full description of crystallization process, both X-ray diffraction method (XRD) as well as differential scanning calorimetry (DSC) were utilized. For magnetoelastic tests, nonmagnetic cylindrical backings were used in order to obtain uniform compressive stresses and enable sample to be wound. In this paper the changes of flux density B as a function of compressive stresses σ (for constant values of the magnetizing field H) for samples at different stages of nanocrystallization are presented.

This paper presents the results of investigation of the influence of nanocrystallization process on magnetoelastic properties and structure of Fe73.5Nb3Cu1Si16.5-xB6+x (x=0; 3) alloys. The magnetoelastic investigation was carried out on ring cores. During the magnetoelastic tests the compressive force (F) was applied perpendicularly to the direction of the magnetizing field (H) in the sample. In the paper the stress dependences of magnetic hysteresis loops as well as changes of flux density B as a function of compressive stresses σ (for constant values of the magnetizing field H) are presented. The experiment was carried out on both alloys after different stages of nanocrystallization. The obtained results confirmed that heat treatment influences not only magnetic but also magnetoelastic properties of Fe73.5Nb3Cu1Si16.5-xB6+x (x=0; 3) alloys.

Amorphous cast irons (with carbon content varying from 12.01 to 15.01 at.%) containing 1 and 2 wt.% of boron, were produced by rapid quenching from the melt in the form of ribbons with thickness of 40–75 μm. The crystallisation process of the amorphous alloys was studied using differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and transmission electron microscopy (TEM).Very strong influence of boron content on thermal stability and crystallisation process of the alloys studied was observed. The increase of boron content from 1 to 2 wt.% resulted in the increase of crystallisation onset temperature by about 100 K and in the change of crystallisation mode. The number of crystallisation stages, observed during calorimetric studies at temperatures reaching 1000 K, drops from three to one when boron content increases from 1 to 2 wt.%. This indicates a change from primary to eutectic mode of decomposition of the amorphous phase, although in both cases similar crystallisation products are formed: α-Fe(Si) and Fe 3 (C,B). In primary crystallisation mode, dendritic crystals of α-Fe(Si) are formed and in eutectic crystallisation of both phases, small elongated crystallites are observed.

High temperature nanocrystalline alloys were prepared by partial replacement of iron by cobalt in the Finemet type alloy. The (Fe1–xCox)73.5Cu1Nb3Si13.5B9 (x=0.136–0.68) ribbons were obtained by melt-spinning technique and their chemical composition was determined by means of X-ray microanalyser. The effect of heat treatment, within the temperature range of 733–833 K, on magnetic properties of the alloys was examined. The structure of partially crystallized alloys was investigated using differential scanning calorimetry (DSC), X-ray diffractometry (XRD), and transmission electron microscopy (TEM). The AC (50 Hz) magnetic properties (coercivity, magnetic induction) of the Fe–Co–Cu–Nb–Si–B alloys were also studied. The effect of partial substitution of iron by cobalt on the structure and magnetic properties of the (Fe1–xCox)73.5Cu1Nb3Si13.5B9 alloys annealed in various temperatures and the thermal stability of magnetic properties of the alloys have been discussed.

(Fe 1-x Co x ) 73.5 Si 13.5 B 9 Nb 3 Cu 1 (x = 0-0.8) nanocrystalline alloys were prepared by annealing melt-spun amorphous precursor. According to X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies, the nanocrystalline phase consist of Fe-Co-Si bcc nanocrystals (10-20 nm). The room temperature properties have been studied in the whole compositional range. The coercive field remains low (< 10 A/m) up to x = 0.2 and jumps to values higher than 40 A/m for higher Co content. However, the annealed Co-rich alloys exhibit a better high temperature behaviour: the induction and coercivity were found to vary little up to 300 C and even 500 C in some cases. This result confirms that these alloys are good candidates for high temperature applications provided the composition and treatment are optimized for this purpose.

Magnetically soft nanomaterials obtained by controlled crystallisation of metallic glasses are the newest group of materials for inductive components. In particular, research is carried out in the field of alloys for high temperature applications. This kind of materials must meet two basic requirements: good magnetic properties and stability of properties and structure. In the present work the magnetic properties and structure of Fe-Co-Hf-Zr-Cu-B (HITPERM-type) alloys were investigated, as well as their stability. Differential thermal analysis, (DTA), X-ray diffractometry (XRD), transmission electron microscopy (TEM), magnetometry (VSM) and quasistatic hysteresis loop recording were used to characterise structure and properties of the alloys investigated. Optimisation against properties and their stability was performed, resulting in formulation of chemical composition of the optimum alloy, as well as its heat treatment.

In the present study, Fe 4 1 Co 4 1 B 1 0 Zr 7 Cu 1 alloy has been investigated in order to evaluate its thermal stability and structure after heat treatment, as well as the impact of heat treatment on magnetic properties. X-ray diffractometry, differential scanning calorimetry, chemical composition microanalysis, transmission electron microscopy, and magnetic hysteresis loop measurement techniques were employed. The crystallisation temperature of the as-quenched alloy is 490°C (continuous heating at 5°C/min). The melt-spun ribbon having 27 μm in thickness was annealed for 1 hour at temperatures from 400 to 700°C. The alloy after treatment at about 550°C underwent primary crystallisation, with the average size of crystals under 20 nm. This specimen shows the coercive field of 38 A/m, as compared to about 160 A/m reported for a similar alloy (Fe 4 4 Co 4 4 B 4 Zr 7 Cu 1 ) with a similar structure, annealed at 600°C.

This work presents the results of the study of the magnetically soft, iron-based bulk metallic glasses, from the viewpoint of their ability to deform in the supercooled liquid region and to resist the tendency to crystallise. The calorimetric measurements of glass transition and crystallisation temperatures (Tg and Tx1 respectively) were employed, accompanied by the measurements of magnetic properties as the monitor of structural changes after heat treatment. It was found that the widest supercooled liquid region was obtained when zirconium was selected as one of the alloying elements, yielding the Tx1–Tg span of about 70 °C. Also, it was observed that the values of Tg and Tx may be controlled by the proportions of the main elements (Fe, Co, Ni), and the glass forming elements (such as B, Nb, Zr). As a guideline, it is suggested that the glassy Fe-based alloys may be maintained in the supercooled liquid state without crystallisation for several minutes, if Tx1–Tg is wider than 50 °C. Basing on this estimation, calorimetric measurements may be a good indicator of the ability of bulk metallic glasses to be suitable for superplastic compaction into larger shapes.

Temperature evolution of the coercivity of nanocrystalline samples of Fe 60 Co 18 Nb 6 B 15 Cu 1 alloy with different crystalline fractions was measured from room temperature up to 690 K. Although room temperature coercivity increases as the nanocrystallization progresses, the thermal stability of the magnetic properties of the system is clearly enhanced as the crystalline volume fraction increases. Microstructure was characterized using room temperature Mossbauer spectra which can be interpreted on the basis of the presence of three different regions: amorphous, crystalline and interface.

The magnetoelastic investigation presented in this paper was carried out on ribbon ring samples made of Fe41,5Co41,5Cu1Nb3B13 amorphous alloy annealed for 1 h in different temperatures ( Ta = 20 , 360, 380, 460 and 540 ∘ C ) in order to achieve different stages of nanocrystallization. During the magnetoelastic tests, nonmagnetic cylindrical backings were used in order to obtain uniform compressive stresses and enable sample to be wound. The changes of flux density B as a function of compressive stresses σ (for constant values of the magnetizing field H) for samples at different stages of nanocrystallization are presented. The results indicate, that both magnetic and magnetoelastic characteristics of Fe41,5Co41,5Cu1Nb3B13 alloy are slightly dependent on annealing process.

(Fe,Co)–Zr,Hf)–Cu–B (HITPERM-type) alloys with variable Hf, Zr and Co content were isothermally crystallised at 500–650 °C for 1 h, and the optimum nanocrystallisation temperature was selected on the basis of the minimum coercive field at room temperature. The quasistatic hysteresis loops were measured at temperature from 20 to 650 °C. Subsequently, the optimally annealed alloys were subjected to long-term annealing at 500, 550 and 600 °C. Working temperature of 600°C is too high for the investigated alloys to maintain stable magnetic properties. Temperature of 550 or 500 °C permits the material to be magnetically stable for a long period. The magnetic hysteresis loops recorded for the nanocrystalline alloys, where Fe:Co ratio is close to 1 and refractory metals content is 7 at.%, prove that coercive field increases slightly with temperature, but remains in the range of 20–40 A/m (depending on the alloy composition) from 20 to 550 °C. This proves that the investigated alloys, after optimisation of chemical composition, may be suitable for high temperature use.

The electric and magnetic properties of the magnetically soft Fe-Si-B-Nb-Cu alloy (Finemet), as a candidate on the absorber at microwaves, have been studied in the frequency range from 0.2 to 10 GHz. Measurements were achieved with the use of the coaxial line technique, where the scattering parameters at broadband frequency range were determined. In this method, using the signal flow graph representation, a method of measuring of the powders inserted in between two plastic walls has been discussed. Based on this attempt, values of relative permittivity (e’, e”) and permeability (μ’, μ”) of the powdered amorphous and nanocrystalline Finemet were shown for four groups of powders with different particle sizes. The measured data refers to pure pulverized Finemet without insulating resin or wax. The obtained results show that the powdered nanocrystalline Finemet containing particles below 25 μm in diameter can have good shielding / absorbing properties (EMC).

FeCo-based soft magnetic alloys of compositions Fe/sub 45/Co/sub 43/Cu/sub 1/B/sub 3.6/Zr/sub 7.4-x/AM/sub x/, where x=3.7 at.% and 7.4 at.%, and the alloying metals (AM) are Nb and Hf and were prepared in the form of amorphous ribbons by a melt-spinning technique. A two-phase microstructure, consisting of /spl alpha/-FeCo nanocrystals and amorphous matrix, was created by partial devitrification of the amorphous alloys during annealing for 1 h at temperatures 500/spl deg/C-600/spl deg/C. The crystallization process of the amorphous alloys was studied using differential scanning calorimetry, X-ray diffractometry, and transmission electron microscopy. The quasi-static hysteresis loop was measured using an inductive method. Partial replacement of zirconium by hafnium improved thermal stability of the amorphous structure and the magnetic properties of the alloys studied. The effect of niobium is opposite. The best magnetic properties were found in the alloy Fe/sub 45/Co/sub 43/Cu/sub 1/B/sub 3.6/Zr/sub 3.7/Hf/sub 3.7/. It was found that the nanocrystallization temperature strongly influences the thermal stability of the magnetic properties of the alloys studied.

Nanomaterials for high-temperature applications must meet two basic requirements: (i) very soft magnetic behaviour at elevated temperature, and (ii) stable properties at elevated temperature for a long time (application time). The latter requirement is related to thermal stability of nanocrystalline structure of these materials. The paper presents the current status of research in the field of magnetically soft nanocrystalline materials, highlighting the influence of alloy composition on magnetic properties and their stability at elevated temperatures during very long time annealing (several thousands of hours at temperature up to 550 °C). It was found that modification of the alloys allows to tailor their chemical composition and manufacturing process to particular application temperature requirements. FINEMETs are the most suitable materials for application at temperature, T , up to 300 °C, FINEMET modified by cobalt (Fe 0.6 Co 0.4 ) 73.5 Cu 1 Nb 3 Si 13.5 B 9 (at.%) for T = 300–350 °C, NANOPERM for T = 350–400 °C and HITPERM (Fe 0.6 Co 0.4 ) 86 Hf 7 B 6 Cu 1 for T = 400–550 °C.

Thermal, mechanical and magnetic properties of (Fe-Co)-(Zr/Si)-Nb-B alloys in the form of rapidly quenched rods of 1.2 mm in diameter were studied. The as-cast alloys with Zr were crystalline, and the alloys with Si were amorphous. Microhardness measured at 50 g load is from 500 to 2000 HV (the less cobalt, the higher), and the compressive strength reaches nearly 4000 MPa for Si doped alloys and 2000 MPa for Zr doped ones. This substantial difference may be attributed to partial crystallinity of the latter alloys. The magnetic hysteresis loops of fully amorphous rods measured under compression, exhibited a clear dependence of permeability vs. stress, proving that iron-based bulk metallic glasses may be promising materials for magnetoelastic force sensors.

Fe 81 P 1 Si 23 Nb 3 Cu 1 metallic glass is used as the parent alloy for a new soft magnetic nanocrystalline material. Two structural transformations of the as-cast alloy are identified during the annealing process. The microstructures created are related to magnetic properties of the nanocrystalline samples.

HITPERM-type alloys were investigated to determine the influence of boron, zirconium and hafnium content on magnetic softness, and to find the crystallisation temperature allowing one to obtain the lowest coercive field, Hc. The second crystallisation stage temperature decreases with the increase of B content, suggesting that boron impairs the stability of the two-phase structure at high temperatures. The addition of Hf improves thermal stability, better than Zr. After annealing for 1 h, Hc of the alloys after the optimum heat treatment is between 17 and 26 A/m. The lowest values of Hc are obtained for the alloys with Hf only.

A new family of Fe–Co based high temperature nanocrystalline alloy was developed using Fe 85− x Co x Nb 5 B 8 P 2 as a precursor amorphous material, which can be cast in air. The nanocrystalline sample presented a flat hysteresis loop with excellent high frequency and high temperature behaviour. The material crystallizes at relative low temperature (400°C), with a relatively low activation energy (2.7 eV) for x =20. The sample annealed at 500°C shows temperature independent soft magnetic properties (Hc around 40 A/m, relative permeability 450 up to 1 MHz) up to the applied annealing temperature.

The effect of partial replacement of Fe by Co in (Fe 1− x Co x ) 73.5 Cu 1 Nb 3 Si 13.5 B 9 alloys ( x =0–0.8) on the nanocrystallization process and on the soft magnetic properties has been investigated. Crystallization process of amorphous alloys was examined by differential scanning calorimetry in order to determine the crystallization temperatures and enthalpies as a function of Co content. The measurements of coercivity, magnetic induction and magnetostriction were carried out at room temperature. It was found that the optimal annealing temperature decreases with the increase of Co content.

Temperature dependence of magnetic properties of nanocrystalline Fe60Co18Cu1B15Nb6−xZrx (x =0, 3, 6) alloys has been studied at different stages of devitrification. Transmission electron microscopy shows nanocrystals of the size �5 nm, which remains almost constant along the nanocrystallization process. Curie temperature of the residual amorphous phase decreases as nanocrystallization progresses for all the studied alloys. Thermal dependence of the exchange stiffness constant is obtained from the measurement of specific magnetization and coercivity as a function of crystalline fraction and temperature for the three studied alloys.

This paper presents the main features of magnetically soft metallic glasses and nanocrystalline materials obtained by controlled crystallization of metallic glasses, a brief description of the principal methods of nanocrystallization as well as the recent developments in nanocrystalline materials for high-temperature applications. Two groups of alloys were investigated: (Fe, Co)-Si-Nb-Cu-B (FINE-MET-type) and (Fe, Co)-(Zr, Nb, Hf)-Cu-B (HITPERM-type). For FINEMET-type alloys it was found that the optimum combination of magnetic properties coercivity, Curie temperature, magnetostriction) is obtained when Fe:Co ratio is about 1:1. For HITPERM-type alloys, the best performance and stability are observed when alloys contain Hf, and the worst in the case of Nb. Optimum Hf content is 7 at.%, and 6 at.% B. The HITPERM-type alloys exhibit good stability of properties at 500°C for at least 700 hours.