High-temperature Soft Magnetic Properties Research Articles

Effect of annealing temperature on structure and high-temperature soft magnetic properties of (Fe0.9Co0.1)72.7Al0.8Si13.5Cu1Nb3B8V1 nanocrystalline alloy

The structure and soft magnetic properties of nanocrystalline (Fe0.9Co0.1)72.7Al0.8Si13.5Cu1Nb3B8V1 alloy annealed at 510−690 °C were investigated by XRD patterns and initial permeability. It was observed that annealing within the ranges of 510−630 °C, only soft magnetic crystalline phase precipitated from the amorphous matrix. With the increase of annealing temperature, the grain size (D) and volume fraction of the crystalline phase (Vcry) both gradually increase from 11.9 nm to 13.7 nm and from 58 % to 89 % respectively. In the meanwhile, the thickness of the amorphous layer (Λ) gradually decreases from 2.37 nm to 0.54 nm. The change of initial permeability with temperature (μi -T curves) showed that the μi declines with increasing temperature. However, the rate of descent is different and the higher annealing temperature (Ta) corresponds to the slower attenuation of μi. The high-temperature μi gradually improves with annealing temperature (Ta) increasing up to 630 °C, and the higher μi of 1500 can be held up to 600 °C. However, the high-temperature μi dramatically deteriorates after annealing at 690 °C due to the precipitating hard magnetic phase from the residual amorphous matrix.

Effect of Ti addition on microstructure and high-temperature soft magnetic properties of nanocrystalline (Fe0.9Co0.1)72.7Al0.8Si13.5B9Cu1Nb3 alloy

The crystallization behavior and microstructure of (Fe0.9Co0.1)72.7Al0.8Si13.5B9-xCu1Nb3Tix(x = 0,1,2) alloys were analyzed by the differential scanning calorimetry (DSC) and X-ray diffractometry (XRD). The soft magnetic properties of alloys after thermal treatment were studied by the temperature dependence of initial permeability (μi-T curves). Experimental results show that the proper addition of Ti can decrease the onset temperature of primary crystallization Tx1 for precipitating soft magnetic phase from 506 °C for x = 0–487 °C for x = 1 and increase the onset temperature of second crystallization Tx2 from 669 °C for x = 0–703 °C for x = 2. The extended onset temperature of second crystallization Tx2 of 703 °C and crystallization temperature interval ΔTx of 199 °C make the 650oC-annealed (Fe0.9Co0.1)72.7Al0.8Si13.5B7Cu1Nb3Ti2 alloy exhibit superior magnetic softness at room- and high-temperatures. And the 610oC-annealed (Fe0.9Co0.1)72.7Al0.8Si13.5B8Cu1Nb3Ti1 alloy shows improved high-temperature magnetic softness at 450–650 °C with respect to Ti-free (Fe0.9Co0.1)72.7Al0.8Si13.5B9Cu1Nb3 alloy.

Microstructure and soft magnetic properties of (Fe0.9Co0.1)73.5Si13.5B9−xNb3Cu1Gex nanocrystalline alloys

The nanocrystalline (Fe0.9Co0.1)73.5Si13.5B9−xNb3Cu1Gex alloys were obtained by partial devitrification of their amorphous precursors. The influence of partial substitution of B by Ge on the microstrucural evolution of these alloys was studied by means of X-ray diffraction (XRD) and differential scanning calorimeter (DSC). The temperature dependence of initial permeability (μi-T curves) for (Fe0.9Co0.1)73.5Si13.5B6Nb3Cu1Ge3 alloys heating–cooling cycled at 450–650 °C was mainly measured. It was found that the Ge doping into (Fe0.9Co0.1)73.5Si13.5B9Nb3Cu1 alloy can reduce the onset primary crystallization temperature (Tx1), enlarge the interval temperature (ΔTx) from 129 °C to 180 °C and improve the high temperature soft magnetic properties, especially for (Fe0.9Co0.1)73.5Si13.5B6Nb3Cu1Ge3 alloy. After annealed at 450–650 °C for the alloy with x = 3, the optimum high temperature magnetic softness was observed in 600 °C-annealed sample, the μi above 1000 at 10 kHz can be kept up to 550 °C, which is due to the higher crystallization phase volume fraction and the thinner amorphous layer thickness and an enhancement of the exchange stiffness in the intergranular region.

Effect of Mo addition on high-temperature soft magnetic properties for air annealed FeCo-based nanocrystalline alloys

Temperature dependence of initial permeability (μi-T curves) for as-quenched and annealed (Fe0.5Co0.5)73.5Si13.5B9Cu1M3 (M=Nb, Mo) alloys were investigated. The Curie temperature of Mo-alloy is decreased by about 5°C compared with Nb-alloy. Although room-temperature μi of Mo-alloy was lower than that of Nb-alloy when nanocrystallized in air, the more stable value of μi and improved high-temperature soft magnetic properties was observed. The reason for the evolution of μi at elevated temperature was also analyzed.

Comment on “High-temperature soft magnetic properties of antiperovskite nitrides ZnNFe3 and AlNFe3” by Yankun Fu, Shuai Lin, and Bosen Wang, J. Magn. Magn. Mater. 378 (2015) 54–58

The authors of the aforementioned manuscript have recently claimed the synthesis of the ternary nitrides ZnNFe3 (=ZnFe3N) and AlNFe3 (=AlFe3N), ordered substituted variants of the binary phase γ‘-Fe4N [1]. While soft ferromagnets of such kind are presently attracting lots of attention, their history dates back for more than half a century. In particular, Al-substituted γ‘-Fe4N has already been mentioned in 1961 [2], and the existence of AlFe3N has also been claimed in 2009 [3] from a two-step ammonolysis reaction combining a high-temperature sintering step and a low-temperature nitriding reaction [4]. Nonetheless, one of us had to withdraw the latter claim after finding out, by means of scanning-electron microscopy and elemental mapping, that all samples of “AlFe3N” consisted of an intimate solid mixture of γ‘-Fe4N and amorphous Al2O3[5]. From what follows, we have strong reasons to believe that the authors of Ref. [1] overlooked our findings [5] and also did not synthesize ZnFe3N and AlFe3N.

Investigation on high-temperature magnetic permeability of Si-rich nanocrystalline (Fe0.9Co0.1)74.5Nb2Si17.5B5Cu1 alloy

The temperature dependence of initial permeability (μi-T curve) for as-quenched and annealed Si-rich (Fe0.9Co0.1)74.5Nb2Si17.5B5Cu1 alloy was investigated. The results showed that fewer Co doping into Fe74.5Cu1Nb2Si17.5B5 can reduce the onset primary crystallization temperature Tx1, enhance the Curie temperature of amorphous phase Tcam, and improve the high-temperature soft magnetic properties. After annealing at 480–650 °C, the common feature of μi-T curve is that the μi increases with T from room temperature and reaches a peak value at a certain temperature, which depends on the annealing temperature Ta, then μi decreases with T. This kind of μi-T curves is different from that of the common Co-contained Finemet-type alloys ever reported. The optimal high-temperature magnetic softness was obtained by annealing at 540 °C, the higher μi of 6500 at 10 kHz can be kept up to 500 °C. Such a magnetic softness at elevated temperature is superior to that of Fe74.5Nb2Si17.5B5Cu1 alloy and other Co-contained Finemet-type nanocrystalline alloys with higher Co content.

High temperature magnetic permeability of Si-rich Finemet-type nanocrystalline (Fe1−Co )74.5Nb2Si17.5B5Cu1 alloys

Structure and magnetic properties of as-quenched and annealed (Fe 0.9 Co 0.1 ) 74.5 Nb 2 Si 17.5 B 5 Cu 1 alloy were mainly investigated by x-ray diffraction and by measuring the temperature dependence of initial permeability ( μ i – T curves) from room temperature up to 700 °C. The as-quenched sample exhibits a lower onset primary crystallization temperature ( T X 1 0 = 475 ° C ) and a larger crystallized interval temperature ( Δ T X = T X 2 0 − T X 1 0 = 201 ° C ) for precipitating the single soft magnetic crystal phase. The Curie temperature of amorphous phase T c a m for as-quenched sample and the Curie temperature of crystalline phase T c c r y for annealed sample were detected to be about 400 °C and 670 °C respectively, which are both higher than that of Fe 74.5 Nb 2 Si 17.5 B 5 Cu 1 alloy. So promising high temperature soft magnetic properties are expected. Annealing temperature ( T a ) exerts a significant effect on room- and high-temperature μ i . When T a is at 600 °C (optimum annealing condition), although, the room temperature permeability of nanocrystalline (Fe 0.9 Co 0.1 ) 74.5 Nb 2 Si 17.5 B 5 Cu 1 alloy was not as high as that of nanocrystalline Fe 74.5 Nb 2 Si 17.5 B 5 Cu 1 alloy, an improved high temperature magnetic softness was observed. The values of μ i for the 600 °C-annealed sample is larger than that of Fe 74.5 Nb 2 Si 17.5 B 5 Cu 1 alloy when temperature increases from 520 °C to 670 °C. The origin for the evolution of initial permeability at elevated temperatures was also analyzed. • Adding 10% Co into Si-rich Fe 74.5 Nb 2 Si 17.5 B 5 Cu 1 alloy decreases T X 1 0 and enlarges Δ T X . • Adding 10% Co into Si-rich Fe 74.5 Nb 2 Si 17.5 B 5 Cu 1 alloy enhances both T c a m and T c c r y . • (Fe 0.9 Co 0.1 ) 74.5 Nb 2 Si 17.5 B 5 Cu 1 alloy exhibits good high temperature magnetic softness.

High temperature soft magnetic properties of (FexCo1−x)73.5Cu1Mo3Si13.5B9 (x=0.5,1) alloys

The microstructure and high-temperature soft magnetic properties of amorphous and nanocrystalline (FexCo1−x)73.5Cu1Mo3Si13.5B9 (x=0.5,1) alloys were investigated. By substituting Co for Fe partially, the onset temperature of primary crystallization, Tx1o, for precipitating α-FeCo soft magnetic phase was decreased from 505 to 460°C, while the Curie temperature of amorphous alloy, TCA⁎, was enhanced from 320 to 455°C. XRD patterns showed that a single α-FeCo crystalline phase with grain size about 16nm was precipitated from amorphous matrix for (Fe0.5Co0.5)73.5Cu1Mo3Si13.5B9 alloy annealed between 460 and 580°C. Although, the room temperature permeability of nanocrystalline (Fe0.5Co0.5)73.5Cu1Mo3Si13.5B9 alloy was not as high as that of nanocrystalline Fe73.5Cu1Mo3Si13.5B9 alloy due to a large saturation magnetostriction (>40ppm), the improved high-temperature magnetic softness was observed for nanocrystalline (Fe0.5Co0.5)73.5Cu1Mo3Si13.5B9 alloy. The initial permeability about 1000 at 10KHz can be maintained up to 600°C, exhibiting a good thermal stability and higher initial permeability at elevated temperatures which is superior to that of Co-free Fe73.5Cu1Mo3Si13.5B9 alloy. The origin of this magnetic softness at elevated temperature was analyzed in terms of Hernando's enhancement effect theory of Curie temperature.

Magnetostriction and effective magnetic anisotropy of Co-contained Finemet nanocrystalline alloys

The microstructure and magnetic properties of Co-contained Finemet nanocrystalline alloys were investigated. By contrasting with Finemet, the Co-contained Finemet nanocrystalline alloys have a broad temperature range for precipitating a single α-FeCo crystalline phrase and a relatively higher Curie temperature of amorphous phase. After full nanocrystallization they exhibit improved high-temperature soft magnetic properties. However the room-temperature permeability of Co-contained Finemet was obviously lower than that of Finemet. For clarifying the reason, the effective magnetic anisotropy ⟨K⟩ and the saturation magnetostriction λs were measured, respectively, and the ⟨K⟩ of Co-contained Finemet is about 100–137 J/m3, which is the same order of magnitude as Finemet, but the λs of Co-contained Finemet-type alloy is much higher than that of Finemet which results in a relatively lower permeability.

Fe-based nanocrystalline soft magnetic alloys for high-temperature applications

We report on improved high-temperature soft magnetic properties in Fe88−2xCoxNixZr7B4Cu1 nanocrystalline alloys. Substituting 5.5 at. % Co and Ni for Fe enhances the magnetization by 5% at ambient temperature and by 30% at 650 °C. The Curie temperature of the residual amorphous phase is also raised significantly (from 67 °C for x=0 to 298 °C for x=5.5), resulting in low coercivities (<30 A m−1) for Fe77Co5.5Ni5.5Zr7B4Cu1 over the temperature range 50–500 °C. The higher magnetization and Curie temperature as compared with other Fe-based alloys, and smaller Co content as compared with (Fe,Co)-based alloys, make this alloy attractive as an affordable high-temperature soft magnetic material.

Microstructure and high-temperature soft magnetic properties of nanocrystalline (Fe 0.65Co 0.35) 78.4Si 9B 9Nb 2.6Cu 1 alloy

Structural characteristics and high-temperature soft magnetic properties of nanocrystalline (Fe 0.65Co 0.35) 78.4Si 9B 9Nb 2.6Cu 1 alloy were investigated. A two-phase nanocrystalline structure composed of the amorphous matrix and the α-FeCo nanocrystallites was obtained by annealing samples at different temperatures from 460 °C to 640 °C for 0.5 h. The temperature evolution of initial permeability was described from room temperature to 730 °C. Coercivity ( H c) and saturation magnetic induction ( B s) were obtained by means of hysteresis loops measurements at room temperature. Results showed that the samples annealed at 550–640 exhibited the improvement of the high-temperature soft magnetic properties. The microstructure exerted a significant effect on the high-temperature magnetic properties. These experimental results were discussed by means of the mechanism of the two-phase random anisotropy model and the exchange coupling through the intergranular amorphous layer.

Pecularities of nanocrystal formation in rapidly quenched (FeCo)MoCuB amorphous alloys

The effect of the substitution of Fe by Co on the enhancement of glass-forming ability limits and subsequent nanocrystallization was studied in a rapidly quenched amorphous system (Fe(x)Co(y))(79)Mo(8)Cu(1)B(12) for y/x ranging from 0 to 1. The effect of Cu on nanocrystallization was investigated by comparison with Cu-free amorphous Fe(80)Mo(8)B(12). Systems partially crystallized at the surface layer were prepared for y/x = 0 using different quenching conditions. The effect of heat treatment of master alloys used for ribbon casting was also assessed. The microstructure and surface/bulk crystallization effects were analysed using transmission electron microscopy and electron and X-ray diffraction in relation to the expected enhancement of high-temperature soft magnetic properties, drastically reduced grain sizes (approximately 5 nm) and Co content. Unusual surface phenomena were observed, indicating the origin of possible nucleation sites for preferential crystallization in samples with low Co content.

High-temperature soft magnetic properties of Co-doped nanocrystalline alloys

In situ hysteresis measurements were used to follow the evolution of soft magnetic properties of various Co containing Finemet- and Hitperm-type nanocrystalline materials. This work is aimed at obtaining the proper chemical composition of nanocrystalline alloys, which can be applied for highest temperatures and is less affected by the inevitable decoupling phenomena, which is common to all two-phase nanocrystalline systems. Experimental results pointed out that in the Co-added Finemet-type alloys the decoupling temperature can be increased by about 50–70 K as compared to Co-free Finemet alloy. Hitperm alloys, close to equiatomic Fe/Co ratio, have much higher decoupling temperature, but their coercivity is an order of magnitude larger at low temperatures compared to the Co-free alloys so their advantage is evident above 400 °C only.

High-temperature magnetic properties of Fe-based nanocrystalline alloy

The high temperature soft magnetic properties of Fe 85.2Zr 3.5Nb 3.5B 6.8Cu 1 amorphous and nanocrystalline alloy were investigated. A Hopkinson peak was observed in the amorphous alloy, which was not observed in the nanocrystalline alloy, and this has been explained by the combination of the anisotropy reduction and the deterioration of magnetic properties. A rapidly decrease in permeability at the Curie temperature of amorphous ( T c am ) was observed in amorphous and partial crystallized nanocrystalline alloys, this phenomenon was disappeared in the highly crystallized nanocrystalline alloys, which was illustrated by the intergrain exchange magnetic coupling through a thin amorphous layer in the two-phase nanocrystalline alloy.