Analysis of reversible resistivity changes during structural relaxation in Co58Fe5Ni10Si11B16 metallic glass using different kinetic forms

Resistivity changes during structural relaxation in pre-annealed Co₅₈Fe₅Ni₁₀Si₁₁B₁₆ metallic glass were measured as functions of annealing temperature (280 to 400° C) and time and their kinetics were analysed using two different kinetic forms. In the case of the non-linear kinetic form which is expressed as ω = exp [- (t/?_m) ⁿ ], the values of mean activation energy,E _a, and mean pre-exponential factor, ?₀, are 1.84 eV and 2.88 × 10^?13 sec, respectively, and it was found that the quality of data fitting to the calculated curve with a constant value ofn = 0.35 was excellent. In the case of the log normal kinetic form which was developed by Nowick and Berry, the values ofE _a and ?₀ are 1.75 eV and 2.4 × 10^?12 sec, respectively, and the quality of data fitting to the calculated curve with a constant value ofβ = 4.5 was good, except for the slight deviation in the large value of log (t/?_m), whereβ is the width of the distribution of relaxation times. The kinetic parameters obtained in the present study were compared with various reported values.     

Stress relaxation in coiled ribbons of Fe40Ni40P14B6 and Fe29Ni49P14B6S6

The stress relaxation at elevated temperatures in coiled ribbons of Fe-Ni base metallic glasses is calculated for both power law creep and Eyring activated flow. The results are compared with experimental data on the spring-back of coiled ribbons after various anneals. Good agreement is obtained for Eyring activated flow, but not for power law creep. Comparison with stress relaxation experiments on straight sections indicates that stress relaxation in coiled ribbons is largely due to transient creep.     

Correlation between thermal stability of soft magnetic properties and structural relaxation in Co58Fe5Ni10Si11B16 metallic glass

Effects of isochronal and isothermal annealings on permeability, coercive field, field-induced anisotropy and electrical resistivity in Co₅₈Fe₅Ni₁₀Si₁₁B₁₆ metallic glass pre-annealed at 743 K for 60 min were examined to clarify the correlation between thermal stability of soft magnetic properties and structural relaxation. It was found that both soft magnetic properties and electrical resistivity changed reversibly, depending on annealing temperature, and the values of activation energy for the changes in these properties were very close, lying in the range 1.8 and 2.0 eV. However, although the deterioration of soft magnetic properties was observed in the specimens annealed below the Curie temperature (T _c), the resistivity changes occurred significantly even in the specimens above (T _c), The results strongly suggest that the changes in soft magnetic properties are attributed to an anisotropic chemical short-range ordering (CSRO) among the cobalt, iron and nickel atoms, and the resistivity changes (structural relaxation) are mainly due to an isotropic CSRO.     

Activation energies of the amorphous-crystalline transformation in the Fe40Ni40P14B6 metallic alloy

The amorphous — crystalline phase change of the metallic glass Fe₄₀Ni₄₀P₁₄B₆ has been studied by examining the change in the electric resistivity, using isochronal and isothermal heating. The isochronal measurements indicate that the crystallization occurs in two stages. One stage appears as a change with pre-annealing in the height of the resistivity-temperature curve at 600 K. This stage characterizes an induction period for recrystallization activated by (1.46+0.03) eV. The other stage, occurring at temperature above 600 K and manifesting itself as a remarkable drop in the resistivity indicates the onset of crystallization. From the isothermal studies of this stage, the energy activating the crystallization is found to be (3.58+0.03) eV. The minimum energy activating the vacancy formation in the crystallized matrix has been calculated to be (1.96+0.03) eV. These results are compared with the corresponding data obtained for the amorphous and crystalline metallic glasses Fe₄₀Ni₄₀B₂₀ and Fe₃₂Ni₃₆Cr₁₄P₁₂B₆.     

Studies of crystallization kinetics of Fe40Ni40P14B6 and Fe80B20 metallic glasses under non-isothermal conditions

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. This revised version was published online in November 2006 with corrections to the Cover Date.     

Structural relaxation in amorphous Fe40Ni40P14 B6 studied by energy dispersive X-ray diffraction

The atomic structure and the structural relaxation of amorphous Fe₄₀Ni₄₀P₁₄B₆ alloy were studied using the energy dispersive X-ray diffraction method. It was demonstrated that the structure of the amorphous alloy can be determined self-consistently with high accuracy by this method. The results indicated that the structural relaxation is a highly collective process involving many atoms, and can be described in terms of the redistribution and transformation of the structural defects. Supported by NSF through Grant DMR 75-15633 and MRL Grant DMR 76-80994     

Correlation between glass transition temperature and melting temperature in metallic glasses

We report that the glass transition temperature (T_g) of a variety of metallic glasses (MGs) correlates with the eutectic or peritectic temperature of two main components corresponding stoichiometric proportion in their binary phase diagram. The correlation suggests that the T_g of MGs is mainly determined by their solvent of two base components, which have composition close to the eutectic and peritectic points in the binary phase diagram and the weakest link in amorphous structure. The results have implications for understanding the structure and glass transition in MGs and for predicting and designing metallic glasses with a desirable T_g.     

Magnetic properties of metallic glass Fe39Ni39Mo4Si6B12

Magnetic metallic glass Fe₃₉Ni₃₉Mo₄Si₆B₁₂ has been studied by the⁵⁷Fe Mössbauer spectroscopy. Mössbauer spectra consist of broad and overlapping six-line pattern below the Curie temperature. The Curie and crystallization temperatures of this metallic glass have been determined to be 575 ± 3 K and 725 ± 3 K, respectively. The hyperfine magnetic field at room temperature is approximately 225 kOe. The reduced hyperfine fields of this sample decrease much faster than that observed for other iron-rich metallic glasses like Fe₄₀Ni₄₀B₂₀, Fe₈₀B₂₀ etc. This behaviour is attributed to the presence of molybdenum atoms in the sample.     

Formation of ferromagnetic bulk amorphous Fe40Ni40P14B6 alloys

Ferromagnetic bulk amorphous Fe₄₀Ni₄₀P₁₄B₆ alloy rods with a diameter of ∼ 1.2 mm can be prepared by means of a rapid quenching technique. If a fluxing technique is also used, amorphous rods with a diameter as large as ∼ 2.5 mm can be synthesized. The critical cooling rate R_c for the glass formation Fe₄₀Ni₄₀P₁₄B₆ is estimated to be on the order of 10² K s^− 1.     

Fe40Ni40P14B6合金磁导率与温度的关系

研究了晶化温度为423℃的Fe40Ni40P14B6非晶合金在200～450℃退火后弱场磁导率μi随温度T的变化.结果表明,退火温度Ta对μi～T曲线的形状有较大的影响.当退火温度Ta低于非晶合金的晶化温度时,μi～T曲线上出现了尖锐的Hopkinson峰,峰值对应的温度为230～265℃,峰的位置随着退火温度的提高而移向高温,说明非晶合金的结构弛豫导致非晶合金的居里温度发生变化.在350～400℃退火后,μi～T曲线在150℃附近出现另一个宽峰,并且在合金从室温至150℃的升温过程中μi线性增加.当Ta高于非晶合金的晶化温度时,表征非晶相居里温度的Hopkinson峰消失,在从室温至400℃的升温过程中磁导率保持较低值不变,超过400℃后随温度的升高,磁导率逐渐上升.解释了磁导率随温度变化的原因并讨论了μi～T曲线的特征与合金相结构的关系及μi～T曲线的实际意义.     

The crystallization of the amorphous alloy Fe40Ni40P14B6

The isothermal transformation behaviour of the metallic glass Fe₄₀Ni₄₀P₁₄B₆ between 320 and 400° C is described. Crystallization occurs by a eutectic mechanism to form Fe-Ni austenite and a body-centred tetragonal phase which is isomorphous with Fe₃P and Ni₃P. The eutectic crystals have a barrel shape such that the c-axis of the tetragonal phase is parallel to the barrel axis. The orientation relationship between the two phases is 1 1 0T 1 1 0 and 0 0 1T 1 1 2. The austenite phase contains (1 1 1) twins.     

Thermal evolution of Fe62.5Co6Ni7.5Zr6Nb2Cu1B15 metallic glass

Thermal evolution of Fe_62.5Co₆Ni_7.5Zr₆Nb₂Cu₁B₁₅ amorphous alloy prepared by one-roll melt-spinning technique was studied by XRD and DTA. The crystallisation process, occurring in several steps, can be summarised as follows: a a + -Fe a + -Fe + -Fe -Fe + -Fe + ZrB₁₂, where a and a are amorphous phases, and a can be indexed as a -Fe (fcc) structure, with a crystalline order on an average distance of 8 Å. The metallic glass demixed on quenching, but component phases tended to mix by exchanging Fe atoms in a temperature range overlapped with the first crystallisation, which yields -Fe nanocrystals (27 Å). Higher temperature exo-peaks correspond mainly to a recrystallisation of the phases formed at lower temperature. It was found that this alloy has nanocrystalline structure also after heating at a well higher temperature than first crystallization. Even after the last exo-peak, the average crystallite size (D) was considerably smaller than that found in the literature for analogous metallic glasses; D values for our alloy were comparable to those of nanocrystalline phases of other systems heat treated below the temperature of exothermal DTA peaks. Extensive oxidation above 600°C, even at a low oxygen content (c _{o 2} 2 ppm), led to a marked modification of the surface layer: two zirconia polymorphs were identified on the surface of the ribbons, and the ratio of -Fe to -Fe content increased with respect to the bulk. Differences in thermal evolution between outer layer and bulk are attributed to a different phase composition and non-uniform distribution since the as-quenched stage.     

The effect of phase segregation during structural relaxation of Fe10Ni65Si10B15 spin glass in the amorphous state

The structural relaxation process of Fe₁₀Ni₆₅B₁₅Si₁₀ amorphous spin glass is described. The ribbon samples were prepared by melt spinning and heat treated using two different annealing processes: AP1 and AP2. The techniques employed to investigate structural changes in the three alloy states as-quenched (AQ), AP1 and AP2 were as follows: transmission electron microscopy, scanning electron microscopy with X-ray analysis, differential scanning calorimetry. Differences were detected in the amorphous structures for two states of relaxation in the alloy. The formation of clusters is proposed for one alloy state and the influence of clustering on the early stages of crystallization is discussed.     

On the free volume kinetics during isochronal structural relaxation of Pd-based metallic glass: effect of temperature and deformation

Free volume changes of amorphous Pd_42.5Cu₃₀Ni_7.5P₂₀ due to structural relaxation under isochronal heat treatments have been quantified using in situ synchrotron X-ray diffraction measurements. The analysis of the first diffraction peak position during the annealing process has allowed us to follow the free volume change during relaxation. The data obtained were successfully fitted to relaxation equations based on free volume model (FVM) and the drawn conclusion is that the FVM remain a useful tool for describing the relaxation phenomena in metallic glasses well below glass transition. The effect of deformation and temperature on kinetics of structural relaxation of the amorphous structure has been quantitatively investigated.