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Delayed nucleation in Fe40Co40P14B6 metallic glass
Abstract
Metallic glass with a nominal composition of Fe40Co40P14B6 (numbers denote at.%) was prepared by the melt-spinning process. The as-quenched FeCo-based ribbons have good soft magnetic properties: the saturation magnetic polarization μ0Ms=1.45 T, a quasistatic coercive force of 4 A m−1 and a maximum differential magnetic permeability of about 110 000 at 60 Hz. Fe40Co40P14B6 glass crystallizes by a eutectic reaction resulting in the face-centered cubic (f.c.c.) solid solution and the body-centered (b.c.) tetragonal (FeCo)3(PB) compound. The crystallization temperatures, determined using differential scanning calorimetry, are approximately 60 K higher than those for Fe40Ni40P14B6. Kolmogorov–Johnson–Mehl–Avrami model has been modified to account for temperature dependencies of nucleation and crystal growth rates and has been employed to quantify the non-isothermal glass crystallization process. Two fitting parameters: the activation energy of atomic transfer across crystal/glass interface Q and crystal/glass interfacial tension σ, which govern crystal nucleation and growth, have been calculated from the set of experimental data of crystallization temperatures at different heating rates. While the estimated crystal growth rates in Fe40Co40P14B6 and Fe40Ni40P14B6 amorphous alloys are rather close, the homogeneous nucleation frequency in the FeCo-glass was found to be essentially lower than that in the FeNi-counterpart. It was concluded that a higher value of the crystal/glass interfacial tension σ is responsible for enhanced thermal stability of the Fe40Co40P14B6 glass.
... To illustrate, characteristics of Fe 80−x Co x P 14 B 6 soft magnetic alloys surpass those of Fe 40 Ni 40 P 14 B 6 Metglas® 2826 [2] widespread in the commercial market. Really, the maximum relative differential permeability of the as-cast ribbons was found to be of about 110,000 and 90,000, the saturation induction μ o M s = 1.45 T and 0.84 T, coercive field 4 A/m and 1.6 A/m, Curie temperature T C = 720 K and 540 K as well as significantly higher thermal stability owing to increased by 60 K crystallization temperature T x = 724 K and 662 K in amorphous Fe-Co and Fe-Ni ribbons, correspondingly [3, 4,2]. Recently, a new series of Fe 80−x Co x P 14 B 6 bulk metallic glasses (BMGs) have been prepared with no glass-forming metal elements other than Fe and Co. Fe-Co-P-B BMGs with the maximum critical diameter as big as 2.0 mm present unique combination of functional properties: μ o M s = 1.53 T, T C = 791 K, onset crystallization temperature T x = 738 K, fracture strength and the plastic strain at room temperature are in the range of 2.69-3.14 ...
... A.M.G. acknowledges decisive input of Dr. V.I. Tkatch adapting KJMA approach at the early stage [4] of Fe-Co-P-B project. ...
... Calculated crystal growth rate U(T) being proportional to τ o −1 exp(-Q/ T) appears to be very close to each other in Fe 40 Co 40 P 14 B 6 and Fe 40 Ni 40 P 14 B 6 alloys due to only 18% difference of activation energy Q and agrees experimental earlier obtained Metglas® 2826 data [23]. Significantly higher thermal stability of Fe-Co-P-B metallic glasses is explained by three orders of magnitude lower nucleation frequency I(T) exponentially proportional to the third power of crystal/glass interfacial energy ς 3 (see Eq. (5) and Ref. [4]). Almost 50% higher ς is responsible for enhanced thermal stability of Fe 80-x Co x P 14 B 6 glasses crystalized at 60 K higher temperatures than Fe 40 Ni 40 P 14 B 6 alloy. ...
Formation mechanism and crystallization kinetics were studied in series of rapidly solidified metallic glasses Fe80-xCoxP14B6 with x = 23, 25, 28, 32, 35 and 40 at.%. As soft magnetic materials, they surpass characteristics of commercial Iron-Nickel Metglas® 2826 alloy: differential permeability of as quenched amorphous ribbons is of about 110000, the saturation induction μoMs = 1.45-1.5 T, coercive field as low as 4 A/m, Curie temperature above 700 K, and significantly higher thermal stability. Isochronal and isothermal differential scanning calorimetry was employed to record the latent heat developed during crystallization. For both regimes, X-ray diffraction revealed two immiscible bcc α-FeCo and bct (Fe,Co)3(P,B) phases that crystallize from completely miscible amorphous glass matrix. Theoretical description of observed kinetics of crystallization process was convincingly accomplished within Kolmogorov-Johnson-Mehl-Avrami model. Enhanced thermal stability of iron-rich Fe80-xCoxP14B6 glasses that crystalize at higher temperatures relies upon higher crystal/glass interfacial energy.
... Functional properties of Fe 80−x Co x P 14 B 6 soft magnetic alloys surpass characteristics of Fe 40 Ni 40 P 14 B 6 metallic glass (Metglas® 2826 [1]) widespread in the commercial market. To compare, the maximum relative differential permeability of the as-cast ribbons was found to be about 110000 and 90000, the saturation induction B s = 1.45 T and 0.84 T, quasistatic coercive field 4 A/m and 1.6 A/m, Curie temperature T C = 720 K and 540 K as well as significantly higher thermal stability owing to increased by 60 K crystallization temperature (T x = 724 K and 662 K) in amorphous Fe-Co and Fe-Ni ribbons, correspondingly [1][2][3]. ...
... The details of fabrication of Fe-Co-P-B series of rapidly quenched ribbons have been published elsewhere [2,3]. In brief, master ingots of alloy with a desired nominal composition of Fe 80−x Co x P 14 B 6 (x = 25, 32, 35, and 40 at.%) were prepared in a quartz crucible by inductive melting of the mixture of pure elemental Fe, Co, B and Co 2 P in Ar atmosphere. ...
We evaluate properties of the prototype of a strain gauge capable to discriminate different strain components: tension and torsion. It makes use of magnetoelastic effect in new Fe48Co32P14B6 metallic glass. As a sensing material, it surpasses characteristics of commercial Iron-Nickel Metglas® alloy: relative differential permeability of as quenched amorphous ribbon is of about 110000, the saturation induction Bs = 1.45 T, coercive field as low as 4 A/m, Curie temperature above 700 K, and significantly higher thermal stability. Different deformation components were determined through the analyses of the shape of hysteresis B-H loops. Fe-Co-P-B glass strain gauge can simultaneously detect as small tensile strains as 1.9 × 10⁻⁵ and less than 0.13 deg/cm of torsional distortions.
... The GFA in cast state and the resistance to amorphous-to-crystallization conversion in 3D printing condition as a function of the maximum crystal growth rate under heating. (a) In cast BMGs, the crystal growth rate during crystallization process does not exhibit any correlation with various GFA; (b) In 3D-printed BMGs, alloy systems with higher crystal growth rate tend to achieve higher amorphous content in its 3D-printed part [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56] . ...
In 3D printing of bulk metallic glasses (BMGs) by selective laser melting (SLM), partial crystallization normally occurs in heat-affected zones (HAZs), which significantly deteriorates the properties of 3D-printed BMGs. To understand which factor dominates amorphous-to-crystalline conversion of 3D-printed BMGs, two representative BMG alloys with different glass forming ability (GFA), i.e., Zr 55 Cu 30 Ni 5 Al 10 (named as Zr55 with high GFA) and Zr 60.14 Cu 22.31 Fe 4.85 Al 9.7 Ag 3 (named as ZrAg with low GFA), were selected for SLM 3D printing, and their crystallization behaviors were comparatively studied. It is revealed that the 3D-printed ZrAg BMG with low GFA always possessed a higher amorphous phase content than the Zr55 BMG with a high GFA under different laser energy inputs. Thermal analysis and TEM observations revealed that crystal growth rate is the crucial factor for the resistance against amorphous-to-crystalline conversion in 3D-printed BMGs, as the ZrAg system exhibited much lower crystal growth rate although it has a lower GFA. The different crystal growth behavior of the two BMGs is associated with their different crystal-lization mechanisms: ZrAg BMG follows the mode of primary-type crystallization with multiple phases formation, leading to a low crystal growth rate, while Zr55 BMG follows the mode of polymorphous-type crystallization, which is characterized with formation of a simple crystalline phase, thus leading to a high crystal growth rate. The present work sheds light on the understanding of crystallization mechanism in 3D-printed BMGs and provides a guide for selection or design of BMG compositions for 3D printing.
... The details of fabrication of Fe-Co-P-B series of rapidly quenched ribbons with the cross section of 1×0.03 mm 2 have been published elsewhere [6,7]. Our amorphous Fe 40 Ni 40 P 14 B 6 ribbon and commercial Ni wire with the diameter of 0.3 mm were served as reference samples. ...
We present and compare results of measurement of saturation magnetostriction constants of amorphous ribbons Fe 80- x Co x P 14 B 6 ( x = 23, 25, 28, 32, 40 at.%) and the reference Fe 40 Ni 40 P 14 B 6 specimen employing Narita and Becker-Kersten methods. We also modified a strain gauge-based method to enable measurements of complete magnetic field dependence of magnetostriction coefficients.
... The amorphous structure composition allows improving some the physical property, when a variation of stoichiometry determines limits to applicability of metallic glasses. Today a industry apply metal glass on based F e − N i − P − B, but replacement N i to Co [1][2][3] lead to increased thermostability. ...
We report about formation mechanism, crystallization kinetics and magnetic properties observed in the series of rapidly solidified F e80−xCoxP14B6 metallic glasses with x = 25, 32, 35 and 40 at.%. Magnetic soft F e80−xCoxP14B6 metallic glasses have 15–25 µm thick and 2–8 mm wide. The ribbon samples were created to meltspun onto the massive copper wheel from the RF-melted superheated master ingots.
... Magnetic properties of rapid quenched Fe 80-x Co x P 14 B 6 metallic glasses surpass characteristics of Fe 40 Ni 40 P 14 B 6 magnetosoft material (Metglas 2826) widespread in the commercial market. Really, the maximum relative differential permeability of as quenched Fe 80-x Co x P 14 B 6 ribbons is about 110000, the saturation induction B s = 1.45 T, quasistatic coercive field as low as 4 A/m, Curie temperature above 700 K, significantly higher thermal stability due to increased by 60 K crystallization temperatures, low hysteresis loss of about 0.26 W/kg in the saturation mode at frequency of 100 Hz [1][2][3]. ...
The paper presents the possibility to build a tension gauge capable to discriminate different kinds of deformations: compression and twisting (induced by torsion strain) based on the magnetoelastic effect in new metallic glasses Fe80−x Cox P14B6. Applied loads increase coercive field H c, saturation induction B s and rectangularity of magnetic hysteresis loop. For example, hysteresis loop traced for 1 mm narrow, 50 cm long and 30 μm thick Fe40Co40P14B6 straight ribbon subjected to longitudinal stress of 346 MPa shown increased B s from 1.24 to 1.7 T and squareness from 0.55 to 0.88 compared to unloaded specimen. For twisting, on the contrary, both squareness and coercive field vary whereas the value of B s remains unchanged.
... Although a lot of new filmy and bulk metallic glasses were discovered recently, magnetosoft Fe-, Ni, and Co-based amorphous alloys remain to be the reference materials to engineer preassigned nanocrystalline structure and to explore its relation to magnetic properties. Early it was shown that the replacement of Ni by Co in the wellknown Fe 40 Ni 40 P 14 B 6 composition raises significantly a thermal stability of metglas [1,2]. In this paper we investigate how Fe-to-Co concentration ratio defines properties of as-quenched and crystallized Fe 80-ξ Co ξ P 14 B 6 alloys. ...
Crystallization kinetics and magnetic properties were studied in series of rapidly solidified metallic glasses Fe80-ξCoξP14B6 with ξ = 25, 32, 35 and 40 at. %. Differential scanning calorimetry (DSC) was employed to determine crystallization temperature and to demonstrate the incubation phenomenon at isothermal annealing. Fitting DSC traces recorded in non-isothermal and isothermal regimes, we obtained the same activation energy Q. It describes atomic transfer across crystal/amorphous interface in Kolmogorov-Johnson-Mehl- Avrami (KJMA) model of the transition of metallic glasses into crystalline state. As-quenched metglas ribbons have amorphous structure and superior soft magnetic properties: coercive field 4 A/m, ac magnetic permeability as high as 110 000 at 60 Hz.
(Fe40Ni40B19Cu1)97Nb3 magnetic amorphous alloys have been prepared by a melt-spun method and their crystallization behavior and kinetics have been investigated. The results showed that under non-isothermal conditions, the growth process is easier than nucleation process for both precipitated phases ((Fe,Ni)23B6 and γ(Fe,Ni) ) and the activation energy (Ea2427.03kJ mol-1) for γ(Fe,Ni) phase is higher than that of (Ea1275.11 kJ mol-1) for (Fe,Ni)23B6 phase. Under isothermal conditions, the energy released during the whole crystallization process is independent of annealing temperature and the crystallization parameters fit well with Kolmogorov-Johnson-Mehl-Avrami (KJMA) model. The nucleation activation energy (En) and growth activation energy (Eg) are 429.2 kJ/mol and 417.2 kJ/mol. Based on the values of Avrami exponent n, the transformation process can be divided into three different stages: Stage I: n≈2.5; Stage II: 2.5＜n≤3; Stages III: n＞3. The whole crystallization process from interface-controlled one-dimensional growth convert into interface-controlled three-dimensional growth.
Becker-Kersten method, which involves observing hysteresis M-H loops under mechanical stress, was applied to measure magnetostriction properties in amorphous rapid quenched ribbons Fe80-x Cox P14B6. It is shown that magnetostriction constant increases with the growth of cobalt atomic content from (1.75 ± 0.13)×10⁻⁶ for x = 25 to (1.60 ± 0.05)×10⁻⁵ for x = 40.
The crystallization processes at constant rate heating and under isothermal conditions of amorphous Fe40Ni40P14B6 and Fe40Co40P14B6 alloys are studied by differential scanning calorimetry, electrical-resistance measurements and transmission electron microscopy. The quantitative comparative analysis of both kinetic and structural experimental data is performed within the classical crystallization theory, and the values of the specific free energy of the crystal glass interface and the effective interfacial diffusion coefficient, which determine the crystal nucleation and growth rates in these glasses, are estimated. As shown, the enhanced thermal stability of the Fe40Co40P14B6 glass arises caused mainly by the essentially lower values of the apparent diffusion coefficient and somewhat higher crystal-glass interfacial energy. The non-steady state behaviour of homogeneous nucleation in the glasses investigated is revealed from the analysis of isothermal crystallization with non-monotonic changes of Avrami exponent vs. annealing temperature, and temperature dependences of the characteristic transient times are determined.
The aim of this work is to derive a more exact expression for the critical cooling rate and to verify it experimentally on the systems As 2Se3, AsSeI, Cu5[As2Se 3]95, Cu15[As2Se3]85, and Cu15[AsSe1.4I0.2]85. We assume that in addition to the growth of the nuclei, one should take into account the continuous increase in their number, i.e. the occurrence of new nucleation events. The obtained equation shows the dependence of the ratio of crystalline phase volume on the critical cooling rate. In principle, this relation allows for the calculation of the cooling rate b that should be applied under the condition that the crystallization rate does not exceed a value α0, given in advance. The calculated cooling rates for the investigated systems can be considered as more exact compared to those previously reported for similar systems and are in agreement with our previous experimental findings.
The Co-based amorphous magnetic nano-particles with multi-composition have been prepared by chemical alloying. The composition, particle size, structure and properties have been studied by using chemical analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), physisorption analyzers and physics property measure system (PPMS). It is indicated that the amorphous magnetic particles of Co-Fe-Ce-B with nano-sizes can be prepared by chemical alloying in mild experiment condition.
The Fe-Ni-Sb-B amorphous alloy has been prepared by a solid-solid chemical reaction of ferric trichloride, nickel chloride, antimony chloride and potassium borohydride powders at room temperature. The inductive couple plasma study indicates that the resultant is composed of Fe 5.38 %, Ni 56.19 %, Sb 29.02 % and B 0.44 %. The XRD and thermal analysis show that the alloy is a non-strict sense amorphous alloy which constituted with NiSb and FeNiB. The TEM image shows the resultant is spheroidicity particles which average size is estimated to be 20-30 nm. The mole ratio of the metal salts has been determined to be 1.0:1.0:0.25 to get the amorphous alloy. The largest saturation magnetization value of the 17.35 emu/g is obtained.
The possibility of synthesizing bulk amorphous alloys with additions of B and P to commercial cast iron (Ci) of the chemical composition Fe 81:5 Si 3:8 C 14 Tm 0:7 (at.%) was investigated. The effect of the B and P concentration on thermal stability, bulk glass forming ability (BGFA) and microstructure was studied by calorimetric (DSC and DTA) mea-surements as well as by X-ray diffraction. With the addition of 8.42 and 12.17 B to the commercial Ci bulk amorphous alloys with very wide supercooled liquid regions (77 and 81 K, respectively) could be produced. The partial replacement of Ci by B and P atoms increases the thermal stability and the BGFA. The kinetics of crystallization was investigated both by linear heating and by isothermal DSC measurements. The changes in the microstructure of the crystalline phases formed during linear heating were studied during further isothermal annealing at 833 K.
The effect of P addition on the thermal stability and on the bulk glass
forming ability (BGFA) of cast iron based CiPxB4.35 (x = 4.35, 8.65, 10
at%) amorphous alloys was investigated by calorimetric (DSC and DTA)
measurements. The amorphous alloys were prepared by melt spinning and by
centrifugal copper mold casting. The crystallization kinetics was
studied by DSC in the mode of continuos times linear heating and it was
found that, both the glass transition temperature, Tg and the
crystallization peak temperature, Tp are shifted to higher temperatures
with increasing heating rate. The partial replacement of Ci by P atoms
increases the thermal stability of the amorphous state and the BGFA.
Bulk amorphous rods with diameters of 1, 1.5, 2, 2.5, and 3 mm as well
as sheets with 1 × 4 mm2 cross-section were prepared by
centrifugal copper mold casting and the amorphicity of the melt-spun
ribbons and of the mold cast rods was investigated by XRD, and HRTEM.
The effect of processing histories (fluxing and pre-annealing) on the amorphous structure and the crystallization kinetics of amorphous Fe40Ni40P14B6 alloy prepared by melt spinning has been studied by differential scanning calorimetry, X-ray diffraction, transmission and scanning electron microscopy. For isothermal crystallization, an incubation time exists, and for isochronal crystallization, an abnormally sharp crystallization peak (with the transformed fraction corresponding to the transformation-rate maximum f
p as less than 0.632) occurs. Subjected to fluxing and pre-annealing, the incubation time (in isothermal crystallization) decreases, whereas the initial crystallization temperature (in isochronal crystallization) declines as well as the less sharp crystallization peak and f
p approaches 0.632. A kinetic model considering transient nucleation is proposed and analyzed, which could describe well the singular crystallization behavior of amorphous Fe40Ni40P14B6 alloy. A recipe based on the kinetic model is also proposed to obtain the kinetic parameters from experiment data. Via kinetic analysis and amorphous structural characterization, it is considered that pre-annealing and fluxing promote relaxation of the system close to the meta-stable equilibrium state; the atomic structure becomes more similar to the correspondingly crystallized phase, thus declining the amorphous stability and alleviating the transient effect on nucleation.
The effect of P addition on the thermal stability and on the glass forming ability (GFA) of bulk amorphous sheets and melt-spun ribbons of cast iron Ci100−xPx (x=1.56, 3.1, 4.63, 6.14, 7.63, 9.1 at.%) was studied by calorimetric measurements. Bulk amorphous sheets of mm transverse cross-section were prepared by centrifugal copper mold casting. For the as-quenched ribbons, it was found that only for x=7.63 and 9.1 glass transition temperatures Tg were detected. The reduced glass transition temperatures Tg/Tl (where Tl is the liquidus temperature) are 0.542 and 0.551, respectively. The as-quenched melt-spun ribbons and the bulk amorphous sheets have nearly the same thermal transition and glass forming ability characteristics.
A series of new Fe80−xCoxP14B6 (x=20, 25, 30, 32, 35, 40) glasses has been prepared by melt-spinning technique. The FeCo-based glasses crystallize via one stage eutectic reaction into a mixture of a-Fe (bcc) solid solution and a b.c.-tetragonal Fe3P-like phase at temperatures approx. 50 K higher than the Fe80−xNixP14B6 metallic glasses. The compositional dependence of the crystallization temperatures at constant rate heating of the FeCo-based glasses has a minimum at x=30 that correlates well with the values of the apparent activation energy of crystallization derived from the Kissinger analysis. The as-quenched Fe80−xCoxP14B6 ribbons within the range examined have superior saturation magnetization in comparison with that of the commercial Fe40Ni40P14B6 glass, for example the maximum value of the saturation magnetization Ms estimated from vibrating sample magnetometer measurements is as high as 153 emu/g (about 1.415 T, for a density of 7.42 g/cm3) for the Fe48Co32P14B6 alloy.
The crystallization kinetics of glassy Fe65Nb10B25 melt-spun ribbons is studied by differential scanning calorimetry in the mode of continuous heating and isothermal annealing and by x-ray diffraction and transmission electron microscopy. Continuous heat treatments of the ribbons show the presence of multiple exothermic peaks before melting. The low-temperature peak corresponds to the precipitation of nanoscale Fe23B6 -type crystalline metastable phase, and further annealing leads to its transformation into the metastable Fe3B phase and subsequent formation of bcc-Fe , Fe2B , and FeNbB stable crystalline phases. The nucleation frequency and the growth rate are determined at selected temperatures from the analysis of the microstructures that emerge during the Fe23B6 -type nanocrystallization. The master curve method is used to obtain the apparent activation energy and the Avrami exponent at the nanocrystallization onset. The nanocrystallization kinetics is explained in the framework of the Kolmogorov-Johnson-Mehl-Avrami theory. The rejection of insoluble alloy atoms during primary crystallization, the formation of diffusion layers around the crystals, and the decrease in the nucleation frequency caused by alloy enrichment of the residual disordered matrix is modeled through a soft impingement factor. Estimated values for the interfacial energy that provide a satisfactory agreement between experiments and modeling are derived considering that homogeneous nucleation frequency and interface-controlled grain growth are dominant at the onset of the nanocrystallization. Consequently, the time-temperature-transformation diagram is also drawn and the critical cooling rate estimated for this glass forming alloy.
Effects of full replacement of Ni by Co in the well-known Fe40Ni40P14B6 glass on thermal stability and structure of fully crystallized samples were investigated by differential scanning calorimetry and transmission electron microscopy. Both glasses crystallize via the same eutectic mode however the crystallization temperatures of the Fe40Co40P14B6 glass are about 60K higher. Kinetics of eutectic crystallization of amorphous alloys at constant rate heating and structure of crystallized samples have been investigated by differential scanning calorimetry and transmission electron microscopy, respectively. The values of the specific free energy of the crystal/glass interface and the effective interfacial diffusion coefficient, which define the crystal nucleation and growth in these glasses, were extracted from both the kinetic and structural data using the earlier proposed method. The obtained results showed that the enhanced thermal stability of the Fe40Co40P14B6 glass was caused mainly by the essential lowered values of crystal growth rate.
The effect of a dc current on the crystallization of Vit1A (Zr42.6Ti12.4Cu11.25Ni10Be23.75) and PCNP (Pd40Cu30Ni10P20) metallic glasses was investigated. Samples were isothermally annealed with and without the current, at 623 and 577 K for the two glasses, respectively. Small-angle neutron scattering analyses showed that in the absence of a current, the annealed Vit1A samples were amorphous, but the imposition of a current enhanced the crystallization process, increasing both the size and volume fraction of the crystallites. Similar general observations were seen for the PCNP glass. Differential scanning calorimetry patterns of Vit1A samples indicate a lower thermal stability of samples annealed with a current. © 2004 American Institute of Physics.
Nano-sized amorphous alloy particles with excellent soft magnetic properties have been prepared in Co–Fe–B–P and Co–Fe–V–B–P alloy systems by using a chemical alloying process. In this process, Co, Fe and V ions were reduced by KBH4 and NaH2PO2 in an aqueous solution. The precipitated metal atoms (or atomic clusters) as well as the B and P atoms, which from KBH4 and NaH2PO2 coalesced together and formed multicomponent particles. The study of X-ray diffraction and transmission electron microscopy showed that these particles were amorphous alloy particles. The average particle size was measured to be about 15 nm and the specific surface areas of particles changed from 31.06 to 142.20 m2/g depending on the molar ratio of the components. The largest saturation magnetization value of 1.2 T was obtained in Co73.77Fe3.58B17.46P3.14V1.39 alloy.
Glass-forming ability (GFA) and thermal stability of Fe62Nb8B30, Fe62Nb6Zr2B30 and Fe72Zr8B20 at % amorphous alloys were investigated by calorimetric (DSC and DTA) measurements. The crystallization kinetics was studied
by DSC in the mode of continuous versus linear heating and it was found that both the glass transition temperature, T
g
, and the crystallization peak temperature, T
p
, display strong dependence on the heating rate. The partial replacement of Nb by Zr leads to lower T
g
and T
x
temperatures and causes a decrease of the supercooled liquid region. JMA analysis of isothermal transformation data measured
between T
g
and T
x
suggests that the crystallization of the Fe62Nb8B30 and Fe62Nb6Zr2B30 amorphous alloys take place by three-dimensional growth with constant nucleation rate. Nb enhances the precipitation of the
metastable Fe23B6 phase and stabilizes it up to the third crystallization stage. Zr addition increases the lattice constant of Fe23B6 and, at the same time, decreases the grain size.
The effect of the addition of Ti, V, Cr, and Mn on the magnetic properties of a nanocrystalline soft magnetic Fe–Zr–B alloy has been investigated. The addition of the elements increases both the crystallization temperature and the grain size of α-Fe. After crystallization, these elements are observed in both the α-Fe grains and the residual amorphous matrix. It has been found that V is a useful element to control magnetostriction by keeping the saturation magnetic flux density (Bs) high. The simultaneous addition of V and Mn increases Bs. The alloys with high Bs, above 1.75 T, show good soft magnetic properties as well; the Fe 90 V 1 Zr 6 B 3 alloy exhibits high Bs of 1.75 T and high permeability (μe) of 31 000, and the Fe 89.5 V 0.5 Mn 1 Zr 6 B 3 alloy exhibits high Bs of 1.78 T and high μe of 23 000. These high Bs values are almost the same as that of a Fe-6.5 wt % Si alloy. The alloys also exhibit low core loss. Therefore, nanocrystalline Fe–V–(Mn)–Zr–B alloys are expected to be applied to power electronic devices such as power transformers. © 1999 American Institute of Physics.
We propose a simple and versatile model to understand the deviations from the well-known Kolmogorov-Johnson-Mehl-Avrami kinetics theory found in metal recrystallization and amorphous semiconductor crystallization. We analyze the kinetics of the transformation and the grain size distribution of the product material, finding a good overall agreement between our model and available experimental data. The information so obtained could help to relate the mentioned experimental deviations due to preexisting anisotropy along some regions, to certain degree of crystallinity of the amorphous phases during deposition, or more generally to impurities or roughness of the substrate. Comment: REVTeX, 3 pages, 3 figures, to appear in Applied Physics Letters
This chapter focuses on measurements and theories pertaining to homogeneous nucleation under cooled liquids and glasses that transform to phases of the same composition. The dynamical model describing the cluster evolution appears to be quantitatively correct. Although there are some experimental and theoretical difficulties with the classical theory, there are also many approaches to rectify these problems. At present, there are no experiments that can demonstrate or can refute conclusively the validity of the classical theory in the regime where it is expected to be valid. This is partially because of a lack of knowledge of the correct values for the parameters that are fit by the theory. Better measurements of the steady-state and time-dependent nucleation rates and the free-energy difference as a function of temperature, and the design of new experiments such as the multistep annealing treatments discussed in the chapter are used to test more rigorously nucleation theories. Time-dependent nucleation and the interface kinetics are incorporated into the field-theoretic approaches to give theories that are as widely applicable and, hence, testable as the classical theory.
In differential thermal analysis, the temperature at which the maximum deflection is observed varies with heating rate for certain types of reactions. An expression can be derived relating this variation with the kinetics of the reaction. By making a number of differential thermal patterns at different heating rates, the kinetic constants can be obtained directly from the differential thermal data. Measurements of the variation of peak temperature with heating rate have been made for several minerals of the kaolin group, the values of the kinetic constants determined, and these values compared with corresponding values obtained for both the same samples and similar material by conventional isothermal techniques. Some factors affecting the results are discussed.
We report the results of 59Co spin-echo measurements at 4.2 °K in amorphous alloys of composition (Fe100-xCox)79P13B8, with x=1, 3, 4, 10, 20, 30, 40, 60, 70, 80, 90 and 100. A comparison is made also with the 59Co NMR spectrum in a-Co3B. Evidence is shown for large quadrupolar effects in the dilute alloys. The influence of short-range order on the hyperfine field distribution in concentrated Co alloys is pointed out.
The subject of metallic glasses is introduced. These materials have technological potential, but only if their stability is adequate. It is, therefore, important to study their transformations on annealing, especially structural relaxation. The ferromagnetic Curie temperature, Tc, is a particularly useful parameter for monitoring structural relaxation and it can be measured by differential scanning calorimetry (DSC). The DSC method is convenient and accurate if temperature lags are corrected for. Ways of performing this correction in the DuPont DSC system are reviewed and a new method is proposed and tested. The experimental details of determining the Tc of metallic glasses are given. Finally, the relaxation behaviour of Fe80B20 glass, as studied by measuring its Tc, is reviewed. This behaviour is similar to that of conventional oxide glasses.
The magnetic and structural properties of as-quenched and crystallized Fe73.5Si15.5B7Cu1Nb3 and Fe86Zr7B6Cu1 alloys with Co partially substituted for Fe were investigated. Nanocrystallization takes place only in bcc structures. With increasing Co content the coercivity increases. In the FeCoZrBCu system a maximum Bs of 1.67 T at about 35 at% Co is obtained. With the Co content in both systems, λs passes a maximum in the nanocrystalline state.
Tape wound cores of as-quenched specimens exhibit unsatisfactory soft magnetic properties. Magnetic field annealing gives substantial improvements. Amorphous alloys thus treated could compete with crystalline materials in power transformers.
The crystallization of spin quenched metallic glasses (FeNiCo)0.75P0.16B0.06 Al0.03 has been investigated in the region near the glass transition temperature using differential scanning calorimetry. The effect of the semimetallic component on crystallization was also studied in the Fe and Co based glasses. Some glasses in the CoNi system showed two crystallization peaks and were unstable (Tx ⩽ Tg). The FeCo based glasses were least stable for Fe and Co rich compositions; the most stable glasses in this system were near x = 0.5.Apparent activation energies of crystallization ΔE, were observed to show a close correlation to the relative stability of these glasses. ΔE ranged <70 kcal/mole for more CoNi glasses. The less stable glasses showed a lower ΔE. This behavior is discussed in terms of structure relaxation.
Differential scanning calorimetry is used to determine the crystallisation rate, , on annealing Fe80B20 glass. Crystalline spherulites nucleate randomly in position and orientation, and grow shaped as prolate ellipsoids. It is shown that the Avrami expression relating actual and extended transformed volumes is not strictly valid in this case, but taking it to be a good approximation, and using the experimental Avrami exponent of 3, a simple model for the crystallisation is developed. This assumes an isokinetic reaction with a constant number of nuclei (quenched-in), active instantly, and a time-independent growth rate at any temperature. The model successfully predicts vs T (temperature) on continuous heating, including the effects of pre-annealing. From the fit of experimental and calculated vs T curves the number of nuclei per unit volume, N, is determined. The values (∼ 1018 m−3) are in excellent agreement with direct observation. N is proportional to the inverse square of the quench rate, implying that transient nucleation is important and that the nuclei were produced homogeneously during the quench. The tenth of the ribbon next to the wheel on quenching has no quenched-in nuclei, perhaps due to the nature of the fluid flow during production.
X-ray-absorption fine-structure data of the metal-absorption edges in the amorphous Fe40Ni40P14B6 and Co70(Si,B)23Mn5(Fe,Mo)2 alloys suggest segregation into microphases with different stoichiometric compositions; in the first case the material contains microphases consisting mainly of Ni and P and others of mainly Fe and B. The second material contains microphases with mainly Co-Si stoichiometry and a Mn-Fe-Mo-B mixture in the remaining part of the sample.
The theory of the kinetics of phase change is developed with the experimentally supported assumptions that the new phase is nucleated by germ nuclei which already exist in the old phase, and whose number can be altered by previous treatment. The density of germ nuclei diminishes through activation of some of them to become growth nuclei for grains of the new phase, and ingestion of others by these growing grains. The quantitative relations between the density of germ nuclei, growth nuclei, and transformed volume are derived and expressed in terms of a characteristic time scale for any given substance and process. The geometry and kinetics of a crystal aggregate are studied from this point of view, and it is shown that there is strong evidence of the existence, for any given substance, of an isokinetic range of temperatures and concentrations in which the characteristic kinetics of phase change remains the same. The determination of phase reaction kinetics is shown to depend upon the solution of a functional equation of a certain type. Some of the general properties of temperature‐time and transformation‐time curves, respectively, are described and explained.
Following upon the general theory in Part I, a considerable simplification is here introduced in the treatment of the case where the grain centers of the new phase are randomly distributed. Also, the kinetics of the main types of crystalline growth, such as result in polyhedral, plate‐like and lineal grains, are studied. A relation between the actual transformed volume V and a related extended volume V1 ex is derived upon statistical considerations. A rough approximation to this relation is shown to lead, under the proper conditions, to the empirical formula of Austin and Rickett. The exact relation is used to reduce the entire problem to the determination of V1 ex, in terms of which all other quantities are expressed. The approximate treatment of the beginning of transformation in the isokinetic range is shown to lead to the empirical formula of Krainer and to account quantitatively for certain relations observed in recrystallization phenomena. It is shown that the predicted shapes for isothermal transformation‐time curves correspond well with the experimental data.
The theory of the preceding papers is generalized and the notation simplified. A cluster of molecules in a stable phase surrounded by an unstable phase is itself unstable until a critical size is reached, though for statistical reasons a distribution of such clusters may exist. Beyond the critical size, the cluster tends to grow steadily. The designation ``nuclei'' or ``grains'' is used according as the clusters are below or above the critical size. It is shown that a comprehensive description of the phenomena of phase change may be summarized in Phase Change, Grain Number and Microstructure Formulas or Diagrams, giving, respectively, the transformed volume, grain, and microstructure densities as a function of time, temperature, and other variables. To facilitate the deduction of formulas for these densities the related densities of the ``extended'' grain population are introduced. The extended population is that system of interpenetrating volumes that would obtain if the grains granulated and grew through each other without mutual interference. The extended densities are much more readily derivable from an analysis of the fundamental processes of granulation and growth. It is shown that, under very general circumstances, the densities of the actual grain population may be expressed simply in terms of the extended population.
The dependence of the crystallization temperature on the heating rate was measured for five conventional melt spun metallic glasses. The results obtained, together with similar data taken from the literature, were analyzed using the Kissinger method. It is shown that application of this method to glass transition and crystallization of metallic glasses leads to unreasonably high apparent attempt frequencies, by many orders of magnitude above the Debye frequency. It is concluded, in accordance with some remarks available in the literature, that this method gives obscure values of the activation parameters of glass transition and crystallization of metallic glasses. A simple equation for approximate estimate of the crystallization onset activation energy of metallic glasses is proposed. © 2000 American Institute of Physics.
Diffusion of several impurity atoms (Cu, Al, Au, and Sb) has been studied in Zr61Ni39 and Fe82B18 amorphous alloys. A definite correlation between the diffusion coefficient (D) and the atomic size of the diffusant is seen for the metal-metal (M–M) alloy, while it is not clear for the metal-metalloid (M–Me) alloy. Based on the present data, as well as other published data in binary amorphous alloys, empirical correlations have been found between (i) the activation energy (Q) and the energy required to form a hole of the size of the diffusing atom in the host alloy, and (ii) the pre-exponential factor (D0) and Q. While the former correlation is seen only for binary M–M type of amorphous alloys, the latter correlation is more general and holds for all types of amorphous alloys. Based on the correlation between D0 and Q, it is proposed that there are two distinct mechanisms of diffusion in amorphous alloys.
This review seeks to summarize the recent developments in the synthesis, structural characterization, properties, and applications in the fields of amorphous, bulk amorphous, and nanocrystalline soft magnetic materials. Conventional physical metallurgical approaches to improving soft ferromagnetic properties have relied on the optimization of chemical and microstructural features. Within the last decade, the development and rapid increase in research of nanocrystalline materials has shown that through proper modifications, revolutionary contributions can be made to better materials’ properties. A wide range of materials’ properties are examined in this review, including: kinetics and thermodynamics, structure, microstructure, and intrinsic and extrinsic magnetic properties.
A model for the glass crystallization at constant rate heating is presented. Based on the model a technique for determination
of the constants involved in the classical equations for the rates of homogeneous nucleation and linear crystal growth is
derived. The effect of the heating rate (in the wide range from 2×10-2 to 16 K s-1) on the temperature of crystallization
as well as on the average grain size in fully crystallized specimens of Fe40Ni40P14B6 and Fe80B20 metallic glasses has been
studied. The values of the interface diffusion coefficient, the rates of nucleation and growth and the volume density of quenched-in
nuclei deduced in the present study are in good agreement with those derived from direct observations. It has been confirmed
that crystallization of Fe80B20 occurs mainly by the three-dimensional growth of the pre-existing crystallites while the Avrami
exponent for the Fe40Ni40P14B6 glass exceeds 4 implying non-steady-state nucleation. It has been demonstrated that the proposed
model allows one to generalize the isothermal and non-isothermal kinetic crystallization curves.
The saturation magnetization σ s and Curie temperature T c for amorphous (Fe 1-x Co x ) 62.5 Si 12.5 B 25 alloys are found to decrease monotonically with increasing Co concentration. The variation of crystallization temperature T cr with x shows a linear increase. These results are different from those of amorphous Fe‐Co‐based alloys with composition near 20 at. % (Si+B). The crystalline samples with x≤0.3 produce a single phase with Cr 5 B 3 ‐type structure. When the Co concentration x is richer than 0.6, the unidentified phase appears, and its Curie temperature drops with x from 910 K for x=0.6 to 426 K for x=1.0.
Annealing of amorphous precursor alloys, with compositions ( Fe,Co) 88 M 7 B 4 Cu 1 (M=Zr, Nb, Hf), above their primary crystallization temperature results in the nanocrystallization of the ferromagnetic α′-FeCo phase. This work describes results of the characterization of these alloys, including morphological and chemical stability of the α′-FeCo phase, examination of alloy compositions, and development of a pseudo-Slater–Pauling curve for the amorphous precursor alloys. Samples with the composition Fe 44 Co 44 Zr 7 B 4 Cu 1 were annealed at 600 °C for 10, 31, 100, 308, 1000, and 3072 h in Ar and examined by x-ray diffraction (XRD) and transmission electron microscopy (TEM). Scherrer analysis of x-ray peak breadths was used to infer only a slight increase in the grain size of the sample annealed for 3072 h (∼60 nm) compared to the samples annealed for short times (∼40 nm). TEM studies revealed a distribution of grain sizes in the material with an average grain size of 42 nm for the 3072 h annealed sample. Samples annealed at higher temperatures exhibited the additional minority phases ( Fe,Co) 3 Zr and ZrO. XRD analysis of the samples annealed for extended times at 600 °C do not indicate any formation of these phases, even in the sample annealed for 3072 h. TEM indicates the formation of minority phases, probably resulting from the devitrification of the amorphous grain-boundary phase and/or oxidation upon extended annealing. Differential -
scanning calorimetry results on alloys of composition ( Fe 0.5 Co 0.5 ) 89 Zr 7 B 4 and ( Fe 0.65 Co 0.35 ) 88 Zr 7 B 4 Cu 1 show primary crystallization temperatures of 495 and 480 °C, respectively. © 2000 American Institute of Physics.
Approximations of the Gibbs free energy change for crystallization of an undercooled liquid. ΔG, are discussed and compared. When liquid heat capacity data are available, ΔG can be approximated to various degrees of accuracy depending on the completeness of the data. In the absence of these data, it is necessary to make further approximations. It is shown that Turnbull's [4] simple linear approximation for ΔG is generally applicable to pure metals. A new expression is proposed for use with easy glass forming alloys such as Au81.4Si18.6. An approximation due to Hoffman [1] is not appropriate for use with metals and alloys but is adequate for use with organic substances, such as ortho-terphenyl.
An ageing study or the amorphous alloy, Metglas 2826, has been carried out to examine its high temperature response, in particular to establish whether any change in crystallisation mode occurs at higher temperatures and to attempt a better understanding of the factors controlling the transformation kinetics. At all temperatures, crystallisation takes place by the nucleation and growth of the same eutectic-like crystals. Analysis of the transformation kinetics and microstructures allowed a determination of nucleation and crystal growth rates. The growth rate increases with temperature and can be regarded as diffusionally dependent: values for diffusion parameters may be deduced. The nucleation rate has a maximum at an intermediate temperature range and has been examined on the basis of homogeneous nucleation theory: activation energies for nucleation are shown to vary with temperature in a consistent manner and in reasonable agreement with established material parameters.
Application of amorphous soft magnets in electric-utility and industrial transformers are increasingly being adopted, helping to solve global warming and energy-saving problems. In addition, amorphous metal-based magnetic components are used in power electronics, telecommunication equipment, sensing devices, electronic article surveillance systems, etc. Some magnetic inductors find applications in pulse power devices, automotive ignition coils, and electric power conditioning systems. All of these applications are possible because of faster flux reversal, lower magnetic loss and more versatile property modification achievable in amorphous alloys. Improvements in materials processing and device fabrication technology will continue to take place, which will further increase the universe of application of amorphous soft magnets. Some fundamental problems associated with the applications are mentioned.
Thermal analysis methods are widely used to study crystallization kinetics in amorphous solids. The experimental data is frequently interpreted in terms of the Johnson–Mehl–Avrami (JMA) nucleation-growth model. This paper discusses the limits of such an approach. A simple and convenient method is proposed to verify the applicability of the JMA model as well as the basic assumptions of kinetic analysis. It is shown that the two parameter autocatalytic model includes the JMA model and that is a plausible description of the crystallization kinetics. The main advantage of this model is its flexibility in describing quantitatively the kinetics of complex crystallization processes. The experimental data for crystallization of a chalcogenide glass and zirconia gel analyzed in this paper clearly demonstrate the rather complex nature of these processes. As a consequence, it is very difficult to explore the real mechanism of the crystallization unless some complementary studies are made.
Compositional dependence of saturation magnetization,
magnetostriction and creep-induced magnetic anisotropy is investigated
in amorphous (Fe1-xCox)85B15
alloys. A close correlation of the three quantities was found. An
anomaly centred at x=0.25 may indicate chemical short-range order of the
Fe3Co type in this concentration range. An explanation of the
creep-induced anisotropy behaviour based on the bond-orientational
anisotropy model is presented. It takes into account both the
short-range ordering in the shear centres and medium-range deformations
of their surroundings