Secondary Crystallization Temperature Research Articles

Effect of Mo addition on thermal stability and magnetic properties in FeSiBPCu nanocrystalline alloys

The glass forming ability, thermal stability, microstructure, and magnetic properties of Fe83.3(Si4B8P4)16−xCu0.7Mox (x = 0, 0.5, 1, and 1.5) alloys are studied to investigate the influence of Mo addition. With increasing Mo content, the negative mixing enthalpy (ΔHmix) increases and the Delta parameter (δ) decreases, which leads to a decline in the glass forming ability. The secondary crystallization temperature increases continuously with increasing Mo content. A small amount of Mo improves sufficiently the thermal stability of the alloy system, which can bear higher temperatures (up to 520 °C) for longer time (up to 40 min) without the formation of compounds because of their increased activation energy. The saturation magnetic flux density (Bs) decreases from 1.78 to 1.68 T with increasing Mo content as a result of the lower volume fraction of the α-Fe phase. Optimum magnetic properties with Bs = 1.74T and Hc = 8.2A/m are achieved in Fe83.3(Si4B8P4)15Cu0.7Mo1 ribbon.

Radio‐Frequency Rapid Thermal Processing Enabling Spatial Phase Transformation and Nanocrystallization of Soft Magnetic Amorphous Alloys

Thermal processing of soft magnetic amorphous and nanocrystalline alloys is explored under the influence of radio‐frequency induction‐heating techniques. Direct induction‐heating concepts based on longitudinal and transverse flux heating are examined and the details of electromagnetic fields interaction with metallic strips are discussed by analytical calculations as well as finite element analysis. Initial experimental results confirming spatial control of phase transformations and nanocrystallization within a single strip of Finemet Fe‐based amorphous ribbons are reported. The degree to which primary and secondary crystallization temperature are achieved depends on the spacing between the ribbon relative to the induction coil as well as the coil design and configuration. For transverse coil configurations, the local temperature and therefore microstructural evolution is different across the lateral dimension of processed ribbons, with reduced gap sizes producing enhanced peak temperatures and larger temperature distributions with greater spatial variation in microstructure. In addition, indirect susceptor‐based induction heating under tension is performed and the impact of microstructure is demonstrated. Herein, potential for exploiting spatially optimized phase transformations is illustrated through electromagnetic field–assisted processing in a scalable manufacturing process with amorphous and nanocrystalline soft magnetic alloys.

Effects of La on Thermal Stability, Phase Formation and Magnetic Properties of Fe–Co–Ni–Si–B–La High Entropy Alloys

The microstructure, phase formation, thermal stability and soft magnetic properties of melt-spun high entropy alloys (HEAs) Fe27Co27Ni27Si10−xB9Lax with various La substitutions for Si (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) were investigated in this work. The Fe27Co27Ni27Si10−xB9La0.6 alloy shows superior soft magnetic properties with low coercivity Hc of ~7.1 A/m and high saturation magnetization Bs of 1.07 T. The content of La has an important effect on the primary crystallization temperature (Tx1) and the secondary crystallization temperature (Tx2) of the alloys. After annealing at relatively low temperature, the saturation magnetization of the alloy increases and the microstructure with a small amount of body-centered cubic (BCC) phase embedded in amorphous matrix is observed. Increasing the annealing temperature reduces the magnetization due to the transformation of BCC phase into face-centered cubic (FCC) phase.

Structural, thermal, and magnetic properties of Fe79MoxB20−xCu1 magnetic amorphous and nanocrystalline alloys

Fe79MoxB20−xCu1 amorphous and nanocrystalline alloys (x = 2, 4, 6, 8 and 10) were studied to investigate the influence of Mo and B contents on crystallization, structural, and magnetic properties. Samples were prepared by rapid solidification of alloy ingots using a single wheel melt spinner. Primary and secondary crystallization temperatures increased with the Mo content in the alloys. A wide primary phase stability range (~280 °C) is achieved for the Fe79Mo10B10Cu1 alloy. The alloys with x = 8 and 10 exhibited a fine-grained microstructure (~5 nm) of BCC Fe phase after isothermal annealing at the primary crystallization temperature. Magnetization at an applied field of 1.19 × 106 A/m (15 kOe) of the annealed alloys decreases with the Mo content, and coercivity of less than 100 A/m is attained at x = 8 and 10. Grain size increased to ~25 nm for x = 2 and 4 under the same thermal treatment, which resulted in higher coercivities. The Curie temperature of the amorphous alloys was observed to decrease with increasing Mo content, lowering below room temperature at x = 10. A good thermal stability of nanoscale microstructure is characterized for the x = 10 alloy at elevated temperatures (650 °C and 700 °C).

Investigation on the Phase Diagram of LiCl-KCl-NdCl3 Pseudo-Ternary System

The ternary phase diagram of LiCl-KCl-NdCl3 system has been investigated by differential thermal analysis (DTA), followed by characterization of the coexisting phases in the solid state by x-ray diffraction, in order to understand the interactions in the NdCl3-LiCl-KCl ternary system. The results of these experiments showed that LiCl and K2NdCl5 form a non binary join section. This divides the LiCl-KCl-NdCl3 system into two quasi-ternary sections, namely (1) LiCl-KCl-K2NdCl5 and (2) LiCl-K2NdCl5-NdCl3 systems. Both are simple eutectic ternary phase diagrams. The ternary eutectic temperatures and eutectic compositions are determined to be 316 ± 3 °C and 53.9 mol.% LiCl-38.7 mol.% KCl-7.4 mol.% K2NdCl5 in the LiCl-KCl-K2NdCl5 quasi-ternary section, while the other eutectic temperature and composition are determined to be 376 ± 9 °C and 46.2 mol.% LiCl-32.5 mol.% K2NdCl5-21.3 mol.% NdCl3 in the LiCl-K2NdCl5-NdCl3 quasi-ternary section. A quasi-ternary peritectic reaction is observed at 37.7 mol.% LiCl-36.2 mol.% KCl-26.1 mol.% K2NdCl5 at 445 ± 1°C. The primary and secondary crystallization temperatures for the samples are deduced from the heating runs of DTA traces, and the phases responsible for the various thermal events are ascertained. Isothermal sections at chosen temperatures and polythermal liquidus projection with isothermal contours are drawn over the ternary phase field.

Amorphous formation and magnetic properties of Co-containing Fe[sbnd]Si[sbnd]B[sbnd]P[sbnd]Cu nanocrystalline alloys

Fe84.3-xCoxSi4B8P3Cu0.7 (x = 0, 2, 4, 6, 8, and 10 at.%) alloy ribbons were fabricated by melt spinning. Results showed that the FeCoSiBPCu alloys added with 0–10 at.% Co showed improved amorphization. The modified alloys displayed not only high thermal stability but also high heat treatment temperature in the range of 150–160 K. Compared with the other Co-containing alloys, the alloys added with 2–4 at.% Co exhibited a higher saturation magnetization (Ms) of approximately 181–194 emu/g and a lower coercive force (Hc) of approximately 10.2–12.3 A/m, thus showing improved magnetic properties in the melt-spun state. When annealed before the secondary onset crystallization temperature, all alloys crystallized a single α-Fe phase. After annealing at 833 K for 10 min, the alloys added with 8–10 at.% Co showed excellent soft magnetic properties, including a high Ms of 198–200 emu/g and a low Hc of 2.6–2.9 A/m.

Effect of Nb, Si and Cu on the crystallization process and magnetic properties of FeNbBP alloys

The effect of Nb, Si and Cu on crystallization process and magnetic properties of the Fe84Nb1B5P9M1 (M = Nb, Si, Cu) alloys were investigated. The experimental results show that the substitution of P by Nb, Si, or Cu leads to a wider interval between two crystallization exothermic peaks in comparison to that of the Fe84Nb1B5P10 alloy. The addition of Cu decreases the primary crystallization temperature (Tx1) of alloys while the doping with Si increases the Tx1 slightly. It is clear that the secondary crystallization temperature (Tx2) increases with the substitution of P by Nb, Si and Cu. Among the three elements, Nb has the largest effect on the precipitation of Fe(B,P) phases, which is due to the large negative mixing enthalpy of Nb and B, P. Based on the measurement of apparent activation energy, it is found that the shift in secondary crystallization peak to higher temperature is mainly due to the decrease in P content. After optimum annealing treatment, the Fe84Nb1B5P9M1 alloys show magnetic flux density above 1.7 T and coercivity below 10 A/m, which is better than Fe84Nb1B5P10 alloy.

Superior high-temperature magnetic softness for Al-doped FeCo-based nanocrystalline alloys

The temperature dependence of initial permeability (μi-T), the average grain size (D), the Curie temperature of amorphous phase (Tcam) of a series of annealed (Fe0.5Co0.5)73.5Nb3Si13.5Cu1B9−xAlx (x=0, 1, 2, 3) alloys were investigated. The Curie temperature of amorphous phase (Tcam) for the Al-contained alloys decreased compared with the Al-free alloy, but the high-temperature magnetic softness was improved. It was found that the increasing Al content enlarged the interval temperature (ΔTx) between the onset crystallization temperature (Tx1) and the secondary crystallization temperature (Tx2). The μi of 530°C vacuum annealed samples tended to increase both at room temperature (except for x=3 alloy) and elevated temperature when Al replaced B element. The (Fe0.5Co0.5)73.5Nb3Si13.5Cu1B6Al3 alloy exhibited excellent high-temperature magnetic softness, and its higher μi above 1000 can be maintained up to 670°C.

Magnetic properties and crystallization kinetics of (Fe100 − xNix)80Nb4Si2B14 metal amorphous nanocomposites

Fe-Ni based metal amorphous nanocomposites (MANCs) are investigated in the pseudo-binary alloys (Fe100−xNix)80Nb4Si2B14. To optimize the soft magnetic properties of the nanocomposites, primary and secondary crystallization kinetics must be understood. As such, primary and secondary crystallization temperatures are determined by differential scanning calorimetry, and activation energies are calculated, along with the resulting crystalline phases. Time-temperature-transformation diagrams for primary and secondary crystallization in (Fe70Ni30)80Nb4Si2B14 are presented. Saturation magnetization and Curie temperature are determined. Lastly, the shape of magnetization vs. time curves for (Fe30Ni70)80Nb4Si2B14 at various temperatures suggest that the secondary crystal product often consumes some of the primary crystalline product.

Influence of Ge on crystallization kinetics, microstructure and high-temperature magnetic properties of Si-rich nanocrystalline FeAlSiBCuNbGe alloy

The influences of Ge addition on crystallization kinetics, microstructure and high-temperature magnetic property of nanocrystalline FeAlSiBCuNbGe alloy have been investigated. The results showed that doping a small amount of Ge into Fe72.7Al0.8Si17.5B5Cu1Nb3 alloy can lower the activation energy and therefore decrease the glass forming ability. The primary crystalline temperature Tx1 and secondary crystallization temperature Tx2 were slightly decreased. But the addition of Ge enhances the Curie temperature of amorphous phase, which significantly improved high-temperature magnetic softness. Average grain sizes were increased and thickness of intergranular amorphous layer was decreased due to the addition of Ge to alloys. The optimum annealing temperature for Fe72.7Al0.8Si17.5B5Cu1Nb2.6Ge0.4 alloy was obtained at 843K. The reason for the enhancement in high-temperature magnetic softness was systematically analyzed in terms of the evolution of microstructure.

Excellent high-temperature magnetic softness in a wide temperature for FeCo-based nanocrystalline alloy

Structure and initial permeability (μi) of as-quenched and annealed (Fe1−xCox)72.7Al0.8Si17.5B5Cu1Nb3 (x=0,0.5) alloys were investigated. Substituting 50at.% Co for Fe enhances both the Curie temperature of amorphous alloy, TcA, from 325 to 375°C and the secondary crystallization temperature Tx2, for delaying the formation of Fe–B hard magnetic phase from 720°C to 729°C. The correlation between initial permeability and temperature (μi–T curve) for (Fe0.5Co0.5)72.7Al0.8Si17.5B5Cu1Nb3 alloys heating–cooling cycled at 510–640°C was mainly analyzed. The optimum high temperature magnetic softness was found in 550°C-annealed sample, the μi can maintain above 1400 and shows roughly a horizontal linear correlation with T from room temperature up to 600°C, which make this alloy attractive as an affordable high-temperature soft magnetic material.

Magnetic permeability of Si-rich (FeCoNi)-based nanocrystalline alloy: Thermal stability in a wide temperature range

Structure and magnetic properties of as-quenched and annealed Ni5(Fe0.5Co0.5)68.5Si17.5Nb3B5Cu1 alloys were investigated by differential scanning calorimetry, x-ray diffraction, transmission electron microscopy, and the temperature dependence of initial permeability (μi-T curves) from room temperature up to 680 °C. The as-quenched sample exhibits a higher secondary crystallization temperature (Tx2) and a larger crystallized interval temperature (ΔTx = Tx2−Tx1) for precipitating the single soft magnetic crystal phase. Annealing temperature (Ta) exerts a significant effect on room- and high-temperature μi for samples heating-cooling cycled at 510–680 °C. When Ta is at 640 °C, an excellent high temperature magnetic softness was observed in a wider temperature range, and the μi above 1000 at 10 KHz can keep up to 600 °C. The origin of this improved high-temperature magnetic softness was also analyzed.

Microwave permeability of nanocrystalline alloys (Fe0.67Co0.33)78Nb6B15Cu1 and (Fe0.67Co0.33)78Nb6Al6B9Cu1

Amorphous alloys (Fe0.67Co0.33)78Nb6B15Cu1 and (Fe0.67Co0.33)78Nb6Al6B9Cu1 have been prepared by a rapid quench method. Subsequent heat treatments at a temperature between the primary and secondary crystallization temperature give rise to the coexistence of two ferromagnetic phases: amorphous matrix and nanocrystalline grains (α′-FeCo). Microwave permeability of flaky particles have been measured within 1–18GHz. Fitting based on the revised Kittel’s law has uncoupled the effects of two ferromagnetic phases on the microwave permeability via the natural resonance mechanism. Due to its lower magnetic anisotropy field, the amorphous matrix has lower natural resonance frequency than that of α′-FeCo nano grains. Besides, it is found that partial substitution B with Al can effectively abate surface oxidation, but which reduce the saturation magnetization and slightly increase the coercivity and resonance frequencies of both ferromagnetic phases.

Effect of Cu additions on the magnetic properties and microstructure of FeCoNbB nanocrystalline alloy

The influence of Cu content and the annealing conditions in the (Fe0.5Co0.5)85−xNb7B8Cux (x=0.5, 1.0, 1.5) soft magnetic alloys on the magnetic properties and microstructure were investigated. The additions of Cu lower the primary and secondary crystallization temperatures and the α→γ phase transformation temperature of the FeCoNbB alloys. The (Fe0.5Co0.5)84Nb7B8Cu1 alloy annealed at 873 K for 3.6 ks, in which α-(Fe, Co) nanocrystalline phase with diameter of 5 nm precipitated from the amorphous matrix, shows the best soft magnetic properties. The resulting (Fe0.5Co0.5)84Nb7B8Cu1 nanocrystalline alloy exhibits a high saturation flux density of 1.88 T, low coercivity of 42 A/m, very high Curie temperature of 1240 K, as well as low core loss of 770 W/kg at 10 kHz under maximum magnetization of 1 T.

The mechanism of the anomalous variation of grain size for Fe-based nanocrystalline alloys

The magnetic properties of the Fe-based nanocrystalline alloys are determined mainly by their grain sizes, and the mechanism of the variation of grain size with annealing temperature is an important issue in the study of nanocrystalline alloys. In this paper, the relationships between grain size and annealing temperature for these alloys within the primary crystallization temperature (Tx1) and the secondary crystallization temperature (Tx2) for 1 h are investigated, and a corresponding model is proposed. The physical mechanism of the fact that the grain size first decreases and then increases with the increase of annealing temperature is explained by using this model. It is found that the grain size has a minimum value when these alloys are isochronally annealed at the temperature near 0.6 times that of the melting point. Theoretical analysis results are found to be in agreement with the experiments data within the investigated temperature range. This investigation provides a means to obtain the smallest grain size quickly.

Effect of composition on the crystallization and magnetic properties of Fe–Co–Si–B–Nb amorphous alloys

The crystallization behavior and magnetic properties of Fe62Co10Si15−xB18−yNb(x + y)−5 amorphous alloys with x = 0–5 and y = 0–5 were examined. Primary crystallization temperature of Fe62Co10Si15−xB13Nbx and Fe62Co10Si10B18−yNbyalloys increased with the addition of Nb. The primary and secondary crystallization temperatures were well separated when the Nb content is above 4 at%. The alloys with 15–18 at% B showed a distinct supercooled region. The Nb addition decreased the Curie temperature as well as room temperature saturation magnetization. The glassy-type Fe62Co10Si10B18 alloy exhibited good soft magnetic properties as well as a supercooled liquid region of 39 K. The finding of the glassy-type Fe-based alloy without Nb element exhibiting high Bs above 1.4 T is promising for future use as a soft magnetic glass material.

Regulation of Soluble Receptor for TNFα on Conjunctival Epithelial Cells and Correlation with ICAM-1 Upregulation by TNFα and IGE-Activated Conjunctival Mast Cells

The influences of Ge addition on crystallization kinetics, microstructure and high-temperature magnetic property of nanocrystalline FeAlSiBCuNbGe alloy have been investigated. The results showed that doping a small amount of Ge into Fe72.7Al0.8Si17.5B5Cu1Nb3 alloy can lower the activation energy and therefore decrease the glass forming ability. The primary crystalline temperature Tx1 and secondary crystallization temperature Tx2 were slightly decreased. But the addition of Ge enhances the Curie temperature of amorphous phase, which significantly improved high-temperature magnetic softness. Average grain sizes were increased and thickness of intergranular amorphous layer was decreased due to the addition of Ge to alloys. The optimum annealing temperature for Fe72.7Al0.8Si17.5B5Cu1Nb2.6Ge0.4 alloy was obtained at 843 K. The reason for the enhancement in high-temperature magnetic softness was systematically analyzed in terms of the evolution of microstructure.

Dependence of magnetoimpedance effect on nanocrystalline structure of Fe‐based amorphous ribbons

This study investigates the magnetoimpedance (MI) behaviour and its dependence on the nanocrystalline structure due to annealing of nominal composition Fe73.5Cu1Nb3Si13.5B9 metallic glass ribbons. Differential Thermal Analyses have shown two distinct stages of primary and secondary crystallisations at ∼532 °C and ∼703 °C, respectively. XRD, SEM and AFM have shown the evidence of nanocrystallization and surface roughness initiated by changes from glassy to primary crystalline state. Coercivity has decreased near the primary crystallisation temperature and a monotonous increase between the two stages of crystallisation. Beyond the secondary crystallization temperature, the coercivity value remained practically unchanged. Magnetoimpedance ratio (MIR) is found to be sensitive to the annealing temperature. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetic and structural properties and crystallization behavior of Si-rich FINEMET materials

The magnetic and structural properties of an Si-rich grade FINEMET alloy with a composition of Fe 73.5Si 16.1B 6.4Nb 2.9Cu 1.1 in at% [Fe 82.7Si 9.1B 1.4Nb 5.4Cu 1.4 (wt%)] were investigated after primary and secondary crystallization of ribbon samples. Optimally annealed ribbons exhibited a homogeneous microstructure composed of ∼7 nm DO 3 nanocrystals surrounded by the retained amorphous phase. This is similar to the base FINEMET. Also, a chemical partitioning model, especially of Si, on slowly heated ribbons above the secondary crystallization temperature (∼700°C), is presented herein in conjunction with the reaction products and the magnetic transitions. A self-consistent magnetization analysis is presented which for the first time in FINEMET materials correlates a macroscopic approach from the sample magnetization (using experimentally determined microstructural data such as volume fractions of magnetic phases) with an atomistic approach such as nearest-neighbor calculations and the atomic magnetic dipole moments. The estimated magnetic moment exerted by one Fe atom in the as-spun sample is ∼1.67 μ B on average, while that in a unit cell of the DO 3 phase crystallized from the amorphous is estimated as ∼1.85 μ B per Fe atom (∼24.2 μ B per a unit cell of the DO 3 phase).

The coercivity dependence of giant magneto-impedance effect in Fe–Cu–Nb–Si–B based metallic alloy ribbon at different crystalline stages

We have studied the giant magneto-impedance (GMI) effect in one Fe-based FINEMET alloy ribbon with nominal composition Fe73.5Cu1Nb3Si13.5B9 (at %). DTA experiments were conducted to identify the primary and secondary crystallization temperatures. XRD, SEM and EDAX were performed to identify the phases at various crystalline stages. Static magnetic properties of the ribbons were measured using a VSM. Coercivity was found to be a strong function of annealing temperature, and this, in turn depended on the size and type of the crystalline phases. The maximum MI effect of 103.4% was observed at annealing temperature of 600°C. It was found that a small change in DC coercivity as a result of annealing greatly changed the MI ratios of the crystalline ribbons. Annealing above the secondary crystallization temperature caused the precipitation of Fe2B and Fe3B phases, which induced magnetic hardening and eliminates MI sensitivity.