Amorphous phase formation by spray forming of alloys [(Fe0.6Co0.4)0.75B0.2Si0.05]96Nb4 and Fe66B30Nb4 modified with Ti

This paper describes results obtained by spray forming three iron-based alloys, namely [(Fe_0.6Co_0.4)_0.75B_0.2Si_0.05]₉₆Nb₄, Fe₆₅B₃₀Nb₄Ti₁ and Fe₆₃B₂₉Nb₄Ti₄, whose compositions derive from rapid solidification studies, in an attempt to obtain metallic glasses. The [(Fe_0.6Co_0.4)_0.75B_0.2Si_0.05]₉₆Nb₄ alloy presented higher glass-forming ability and showed a high fraction of amorphous phase formation up to a depth of 4 mm in the deposit. On the other hand, the spray formed deposits of the Fe₆₅B₃₀Nb₄Ti₁ and Fe₆₃B₂₉Nb₄Ti₄ alloys showed fully crystalline microstructure, despite the fact that the melt spun ribbons were fully amorphous.     

Air-oxidation behavior of a [(Fe50Co50)75B20Si5]96Nb4 bulk metallic glass at 500–650 °C

The oxidation behavior of a [(Fe₅₀Co₅₀)₇₅B₂₀Si₅]₉₆Nb₄ bulk metallic glass was studied over the temperature range of 500–650 °C in dry air. The oxidation kinetics generally followed the parabolic-rate law, and the parabolic-rate constants (k_p values) of the glassy alloy increased with increasing temperature. The k_p values of the glassy alloy were lower than those of the binary FeCo alloy. The scales formed on the FeCo alloy consisted of Fe₃O₄ and minor Fe₂O₃, while B₂O₃ was also observed on the amorphous substrate, whose formation may be responsible for the slower oxidation rates of the glassy alloy.     

INFLUENCE OF Co ON THE GLASS FORMING ABILITY AND SOFT MAGNETIC PROPERTY OF Fe–B–Y–Nb BULK AMORPHOUS ALLOY

采用吸铸法制备了直径为2---5 mm的[(Fe_1-xCo_x)_71.2B₂₄Y_4.8]₉₆Nb₄ (x=0, 0.1, 0.2, 0.3和0.4) 合金棒. XRD测试表明, 用适量的Co替换Fe可有效提高原始
合金 (Fe_71.2B₂₄Y_4.8)₉₆Nb₄ 的玻璃形成能力, 拓宽非晶形成范围. 热分析结果显示所有的非晶合金均具有高的玻璃转变温度(T_g≥850 K) 和宽广的过冷液态区 (Δ T_x≥97 K). 此外, Co的替换明显改善了原始非晶合金的软磁性能, 其中成分为[(Fe_0.9Co_0.1)_71.2B₂₄Y_4.8]₉₆Nb₄的非晶合金的饱和磁化强度M_s达到26.6 kA/m, 矫顽力H_c仅为59 A/m.热磁实验表明, 随着Co含量的增加, 非晶合金的Curie温度不断升高, 最大值达到577 K, 与初始合金相比提高了100 K, 显著改善了原体系的热磁性能.     

Structural transformations of amorphous iron-based alloys upon abrasive and thermal treatments

Wear resistance and structural changes have been investigated in amorphous alloys Fe₆₄Co₃₀Si₃B₃ and Fe_73.5Nb₃Cu₁Si_13.5B₉ upon wear using a fixed abrasive. The structural studies have been performed by the methods of metallography, electron microscopy, and Mössbauer spectroscopy. It has been shown that the abrasive resistance of amorphous alloys is 1.6–3.1 times lower than that of high-carbon tool steels, which have a close level of hardness. The low abrasive wear resistance of amorphous alloys is caused by the deformation softening of the alloy surface in the process of wear. The major volume of the deformed surface layer of the alloys preserves the amorphous state. Its structural changes upon wear are characterized by the formation of inhomogeneities (fragments with a size of 10–50 nm) and by a decrease in the width of the strongest “halo” in the selected-area electron-diffractions patterns. In the amorphous matrix of the Fe₆₄Co₃₀Si₃B₃ alloy, a strong magnetic texture is formed and a redistribution of atoms occurs, which leads to an increase in the local shortrange order corresponding to FeB, Fe₂B, Fe₃B and α-Fe phases. In microvolumes of a thin (several μm) surface layer, the formation of a nanocrystalline structure (on the order of several volume %) was revealed. A tempering of the Fe_73.5Cu₁Nb₃S_13.5B₉ alloy at temperatures below 500°C does not affect the hardness and wear resistance of the alloy. At 500°C, there occurs an increase in microhardness and wear resistance of the Fe_73.5Cu₁Nb₃S_13.5B₉ alloy as a result of the formation in it of a nanocrystalline structure with the retention of a certain amount of the amorphous phase. The complete crystallization of the alloy at 540°C increases the brittleness of the alloy, which leads to a sharp reduction in its wear resistance.     

High temperature oxidation behavior of FeCo‐based nanocrystalline alloys

This paper describes the dynamic and isothermal oxidation behavior of three different FeCo‐based Fe_38.5Co_38.5Nb₇Cu₁B₁₅, Fe₃₆Co₃₆Nb₇Si₁₀B ₁₁ and Fe_33.5Co_33.5Nb₇Si₁₅B₁₁ alloys and one traditional FINEMET Fe₇₃Nb₃Cu₁Si_15.5B_7.5 alloy. Dynamic and isothermal oxidation measurements in controlled oxidizing atmosphere were performed and the oxidation apparent energy as well as the oxidation behavior was obtained. SEM observations were carried out in order to characterize the oxide layer formed during the oxidation measurements. The apparent activation oxidation energy found for the Fe₃₆Co₃₆Nb₇Si₁₀B₁₁, Fe_33.5Co_33.5Nb₇Si₁₅B₁₁ and Fe₇₃Nb₃Cu₁Si_15.5B_7.5 alloys was about 35 kJ/mol and for the Fe_38.5Co_38.5Nb₇Cu₁B₁₅ alloy was about 70 kJ/mol.     

Structural transformations and tribological properties of amorphous alloys upon wear at room and cryogenic temperatures

The abrasive wear resistance of the Fe₆₄Co₃₀Si₃B₃, Co_86.5Cr₄Si₇B_2.5, Fe_73.5Nb₃Cu₁Si_13.5B₉, and Fe_82.6Nb₅Cu₃Si₈B_1.4 commercial amorphous alloys (ribbon 0.03 mm thick and 12 mm wide) has been investigated under the conditions of abrasive and adhesive wear upon sliding friction. The character of fracture of the surface and structural transformations that occur in these materials upon wear have been studied by the metallographic and electron-microscopic methods. It has been shown that at room and cryogenic (−196°C) temperatures of tests the abrasive wear resistance of the amorphous alloys is two-three times lower than that of tool steels Kh12M and U8. A comparatively small abrasive wear resistance of the amorphous alloys is explained by local softening of these materials in the process of wear. Under the conditions of adhesive wear of like friction pairs at room temperature in air and argon, the amorphous alloys are characterized by the rate of wear that is smaller approximately by an order of magnitude than in steels 12Kh13 and 12Kh18N9. It has been established that upon wear the deformed surface layer of the alloys under study retains a predominantly amorphous state but in local sections of this layer nanocrystalline structures that consist of crystals of bcc and fcc phases and borides are formed. The possible effects of this partial crystallization on the microhardness, friction coefficient, and wear resistance of these alloys have been considered.     

Magnetic, electrical and plastic properties of Fe76Nb2Si13B9, Fe75Ag1Nb2Si13B9 and Fe75Cu1Nb2Si13B9 amorphous alloys

Influence of 1 h annealing in vacuum on magnetic, electrical and plastic properties of Fe₇₆Nb₂Si₁₃B₉, Fe₇₅Ag₁Nb₂Si₁₃B₉ and Fe₇₅Cu₁Nb₂Si₁₃B₉ melt spun ribbons were carefully investigated. It was shown that in all cases soft magnetic properties can be significantly enhanced by applying 1-h annealing at characteristic temperatures T_op. This optimization annealing causes that permeability increases more than 15-times and magnetic losses (tangent of loss angle) achieves a minimum in relation to the as quenched state. Using structural examinations (X-ray and HRTEM) it was shown that for the Fe₇₅Cu₁Nb₂Si₁₃B₉ alloy the optimized microstructure corresponds to a nanocrystalline αFe(Si) phase whereas in other alloys to a relaxed amorphous phase free of iron nanograins. As a consequence of this fact the Fe₇₆Nb₂Si₁₃B₉ and Fe₇₅Ag₁Nb₂Si₁₃B₉ alloys show higher plasticity in comparison to the nanocrystalline Fe₇₅Cu₁Nb₂Si₁₃B₉ alloy. Temperatures of the first stage of crystallization, and related diffusion parameters were determined using measurements of resistivity versus temperature with different heating rates.     

Preparation of Fe-based monodisperse spherical particles with fully glassy phase

In this study, we prepared monodisperse spherical particles of a desired diameter using [(Fe_0.5Co_0.5)_0.75B_0.2Si_0.05]₉₆Nb₄ alloy; the particles were prepared by using an atomization process developed by us. The particles have perfect sphericity and narrow size distribution along with a homogeneous composition. The phase transitions of particles from the fully glassy phase to the crystalline phase via mixed phase structures occurred as the particle diameter was increased; the particles produced in the fully glassy phase in an argon atmosphere had a diameter of less than 300 μm. This allowed the estimation of the intrinsic critical cooling rate for the particles with a fully glassy phase, R_c:R_c varied in the range of 700-900 K/s and depended only on the initial temperature of the alloy melt.     

Structural transformations and wear resistance of abrasive-affected amorphous Fe- and Co-based alloys

The abrasive wear resistance of the Fe₆₄Co₃₀Si₃B₃, Fe_82.6Nb₅Cu₃Si₈B_1.4, Co_86.5Cr₄Si₇B_2.5, and Fe₈₁Si₄B₁₃C₂ amorphous alloys (ribbon 30 μm thick) has been investigated upon sliding over fixed abrasives (corundum and silicon carbide). The character of fracture of the surface and structural transformations initiated in these materials by the abrasive action have been studied by the metallographic, X-ray diffraction, and electron-microscopic methods. It has been shown that the abrasive wear resistance of the amorphous alloys is smaller by a factor of 1.6–2.9 than that of the Kh12M and U8 tool steels possessing approximately the same level of hardness. A pronounced softening of the surface layer of the amorphous alloys in the process of wear, which is characterized by a decrease in their microhardness reaching 12.5%, has been found. It has been shown that in the surface layer of these amorphous alloys upon wear there arises a small amount (on the order of several volume percent) of the nanocrystalline structure, which does not exert a marked effect on the microhardness and wear resistance of the alloys. In the alloys under study, the main factor that is responsible for their comparatively low abrasive wear resistance is their local softening in the process of wear caused by specific features of deformation processes occurring heterogeneously under the action of high shear contact stresses.     

Solidification behavior,glass forming ability and thermal characteristics of soft magnetic Fe–Co–B–Si–Nb–Cu bulk amorphous alloys

The effect of varying Cu content on the bulk glass forming ability (GFA) of (Fe_0.36Co_0.36B_0.192Si_0.048Nb_0.04)_100?XCu_X alloys (X = 0, 0.5, 0.75 and 1.0) is revealed by investigating the thermal behaviors and phase competitions upon solidification. The changes in GFA are interpreted in terms of suppression of consecutive solidification reactions via microstructural and thermal features. Instead of the type of the primary crystallization product originating from the prevalent atomic order in the glass or supercooled liquid, precipitation of faceted binary and higher-order pro-eutectic compounds such as (Fe,Co)₂B and (Fe,Co)NbB from the alloy melt and resulting skewed eutectic coupled zone are correlated with the observed GFA. With the employed centrifugal casting method, the (Fe_0.36Co_0.36B_0.192Si_0.048Nb_0.04)_99.25Cu_0.75 alloy shows the largest critical thickness of 3 mm and the best soft magnetic properties such as 1.58 T saturation magnetization intensity and 11.7 A/m coercivity after annealing.     

Influence of thermal treatment on structure and microhardness of Fe75Ni2Si8B13C2 amorphous alloy

Correlation between hardness of amorphous Fe₇₅Ni₂Si₈B₁₃C₂ alloy and thermally induced structural transformations has been investigated by measuring microhardness in a series of samples heated at different temperatures from 25 to 1000 °C. The alloy has a relatively high hardness in the amorphous state, due to its chemical composition involving silicon, boron and carbon. As the alloy begins to crystallize, microhardness increased and reached a plateau in 500–650 °C temperature region, due to formation composite structure involving the small nanocrystals of α-Fe(Si) and Fe₂B phases dispersed in the amorphous matrix. After treatment at higher temperatures, the nanocomposite structure is replaced by a more granulated structure, leading to decline in microhardness.     

FeSiBPNbCu alloys with high glass-forming ability and good soft magnetic properties

Effects of Cu addition on the glass-forming ability (GFA), thermal stability, magnetic properties and crystallization process of (Fe_0.76Si_0.09B_0.1P_0.05)_99−xNb₁Cu_x (x = 0, 0.25, 0.5, 0.75, 1) alloys were investigated. The introduction of Cu effectively stimulates the precipitation of the α-Fe(Si) without obvious deterioration of the GFA, and successfully modifies the simultaneous precipitation of α-Fe(Si), Fe₂B and Fe₃(B,P) phases in (Fe_0.76Si_0.09B_0.1P_0.05)₉₉Nb₁ alloy into separable precipitation of each phase at different temperatures during annealing, leading to the enhancement of soft magnetic properties. The saturation magnetic flux density of the representative (Fe_0.76Si_0.09B_0.1P_0.05)_98.25Nb₁Cu_0.75 alloy could be enhanced from 1.43 to 1.51 T after annealing at 530 °C for 10 min due to the precipitation of α-Fe(Si) nanoparticles with a diameter of about 22 nm dispersing randomly in the amorphous matrix. The integration of high GFA and excellent soft magnetic properties makes the FeSiBPNbCu alloys promising soft magnetic materials for industrial applications.     

Influence of thermal treatment on structure development and mechanical properties of amorphous Fe73.5Cu1Nb3Si15.5B7 ribbon

Ribbon-shaped amorphous samples with the stoichiometric composition Fe_73.5Cu₁Nb₃Si_15.5B₇ prepared by the melt spinning process were annealed at temperatures ranging from 693 K to 1123 K for 1 h under vacuum. In the early annealing stage, the alloy undergoes a specific nucleation process where Cu clusters precipitate from an amorphous matrix. Further heating initiates the partial crystallization of alloy forming the α-Fe–Si nanocrystallites. Subsequent Vickers hardness tests showed high values depending on the annealing temperature. It was found that the hardening process includes two stages. This behavior correlates well with results of density dislocation calculations. A crystallite size of 10 nm for the α-Fe–Si particles correlated very well with a maximum hardness of the material.     

Microstrucural characterization of gas atomized Fe73.5Si13.5B9Nb3Cu1 and Fe97Si3 alloys

Powder particles of Fe_73.5Si_13.5B₉Nb₃Cu₁ and Fe₉₇Si₃ soft magnetic alloys have been prepared by gas atomization. The gas atomized powder was microstructurally characterized and the dependence of coercivity with the composition and powder particle size investigated. As-atomized powder particles of both compositions were constituted by a bcc α-Fe (Si) solid solution. The Fe_73.5Si_13.5B₉Nb₃Cu₁ powder particles presented a grain microstructure with dendrite structure, which dendrite arms were enriched in Nb. The coercivity increased as the particle size decreased, with a minimum coercivity, of 5 Oe, measured in the Fe₉₇Si₃ alloy in the range of 50–100 μm powder particle size. The coercive fields were quite higher in the Fe_73.5Si_13.5B₉Nb₃Cu₁ than in the Fe₉₇Si₃ powder, due to the Nb addition, which produced a phase segregation that leads to a noticeable magnetic hardening.     

Thermally induced crystallization of Fe73.5Cu1Nb3Si15.5B7 amorphous alloy

Thermally induced crystallization of Fe_73.5Cu₁Nb₃Si_15.5B₇ amorphous alloy occurs in two well-separated stages: the first, around 475 °C, corresponds to formation of α-Fe(Si)/Fe₃Si and Fe₂B phases from the amorphous matrix, while the second, around 625 °C, corresponds to formation of Fe₁₆Nb₆Si₇ and Fe₂Si phases out of the already formed α-Fe(Si)/Fe₃Si phase. Mössbauer spectroscopy suggests that the initial crystallization occurs through formation of several intermediate phases leading to the formation of stable α-Fe(Si)/Fe₃Si and Fe₂B phases, as well as formation of smaller amounts of Fe₁₆Nb₆Si₇ phase. X-ray diffraction (XRD) and electron microscopy suggest that the presence of Cu and Nb, as well as relatively high Si content in the as-prepared alloy causes inhibition of crystal growth at annealing temperatures below 625 °C, meaning that coalescence of smaller crystalline grains is the principal mechanism of crystal growth at higher annealing temperatures. The second stage of crystallization, at higher temperatures, is characterized by appearance of Fe₂Si phase and a significant increase in phase content of Fe₁₆Nb₆Si₇ phase. Kinetic and thermodynamic parameters for individual steps of crystallization suggest that the steps which occur in the same temperature region share some similarities in mechanism. This is further supported by investigation of dimensionality of crystal growth of individual phases, using both Matusita–Sakka method of analysis of DSC data and texture analysis using XRD data.     

Viscosity and fragility of the supercooled liquids and melts from the Fe–Co–B–Si–Nb and Fe–Mo–P–C–B–Si glass-forming alloy systems

The dynamic viscosity of four Fe-based bulk metallic glass-forming alloys, [(Fe_0.5Co_0.5)_0.75B_0.2Si_0.05]₉₆Nb₄ (alloy A), {[(Fe_0.5Co_0.5)_0.75B_0.2Si_0.05]_0.96Nb_0.04}_99.5Cu_0.5 (alloy B), Fe₇₄Mo₄P₁₀C_7.5B_2.5Si₂ (alloy C) and (Fe_0.9Ni_0.1)₇₇Mo₅P₉C_7.5B_1.5 (alloy D), was investigated as a function of temperature in the supercooled liquid region, as well as above the melting point. The alloy B is Cu-added alloy A, while the alloy D was obtained upon fine-tuning the alloy C composition. All these alloys may form bulk metallic glasses upon copper mold casting. The viscosities in the supercooled liquid region were calculated using the data obtained upon parallel plate rheometry measurements, as well as upon differential scanning calorimetry (DSC). The values of the supercooled fragility parameter m, 61, 66, 52 and 60 for the alloys A, B, C and D respectively, indicate that these alloys are intermediate glass formers. The behavior of the same alloys, in the molten state, was studied using a high temperature torsional oscillation cup viscometer. The values of the corresponding fragility parameter M was calculated as 5.03, 5.91, 4.25, 4.93 for the alloys A, B, C and D, respectively. They confirm the supercooled liquid behavior and predict that the alloys A and C may form glasses easier than the fine-tuned compositions B and D. Angell plot is constructed for the entire range of viscosities and the values from both regions, i.e. above melting point and supercooled liquid region, fit well with the model.     

Enhancement of plastic deformation in FeCoNbB bulk metallic glass with superhigh strength

The effect of B on the glass-forming ability of FeCoNbB alloys was investigated. Bulk metallic glasses with critical diameters up to 3 mm and superhigh yield strength of 4860 MPa were synthesized in (Fe_0.5Co_0.5)_71−xNb₆B_23+x (x = 0, 2, 3, 4 and 5) alloy system. Besides, Cu was added to the Fe_33.5Co_33.5Nb₆B₂₇ alloy with the aim at enhancing mechanical properties, and it was found that proper amount of Cu addition could effectively improve the compressive plasticity from 1.4% to 3.7% without obvious strength decreasing. The enhancement of plasticity is ascribed to the formation of clusters in Cu-contained FeCoNbB bulk metallic glasses.     

Effects of temperature and pH level on the corrosion behavior of amorphous Co69Fe4.5Nb1.5Si10B15 alloy

The corrosion behavior of the amorphous Co₆₉Fe_4.5Nb_1.5Si₁₀B₁₅ (at.%) alloy ribbon in H₂SO₄ solutions (0.001 M or 0.07 M), NaCl solution (0.07 M), and HCl + NaOH solution were examined as functions of solution temperature and pH. The corrosion potential decreased when either the temperature or pH of the solutions increased. The corrosion resistance of the Co₆₉Fe_4.5Nb_1.5Si₁₀B₁₅ alloy in the 0.07 M NaCl solution was higher than the 0.001 M or 0.07 M H₂SO₄ solutions for a given temperature. The corrosion rate increased exponentially with an increase in temperature and was inversely proportional to the pH in the range of 10^?6 A/cm²～10^?4 A/cm².     

Mechanical properties of a FeCuSiB alloy with amorphous and/or crystalline structures

Fe_76.5Cu₁Si_13.5B₉ alloy rods with a diameter of 3 mm were fabricated using the copper mold suction casting method. Structural characterization revealed that different parts of the rods have different microstructures that comprise a complete amorphous structure, an amorphous-crystalline composite structure and a complete crystalline structure. Compression and nanoindentation testing showed that the hardness, strength and elastic modulus of the alloy increase with the crystalline component. High crack propagation rate and narrow shear bands contribute to the local melting and softening for the complete amorphous structure although it exhibits the lowest calculated value of the static elastic energy density.     

Effect of P on glass forming ability,magnetic properties and oxidation behavior of FeSiBP amorphous alloys

The effect of P on the glass forming ability, soft magnetic properties and oxidation behavior of Fe₇₈B₁₃Si_9-xP_x (x = 0–7) amorphous alloys were investigated. It is found that the proper introduction of P, can effectively improve the glass forming ability and stability of supercooled liquid region. Fe₇₈Si₄B₁₃P₅ BMG, which exhibits high saturation flux density of 1.56 T, was readily made into rod sample with a diameter of 1.5 mm under air casting atmosphere. P bearing alloys also exhibit excellent soft magnetic properties containing low coercivity of 1.7–2.7 A/m, and high effective permeability of 8200–12,200. Slight oxidation can further improve the coercivity to a lower value of 1.1 A/m and the higher effective permeability to 11,900 for the alloys with P content no more than 3 at. %. Excessive addition of P may deteriorate the glass forming ability, soft magnetic properties and oxidation behavior. Magnetic domain revealing the magnetization process of the amorphous ribbons were characterized to explain the effect of P on magnetic properties and oxidation behavior.