Department of Physics

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The effects of microstructure on the micromagnetic Barkhausen signal emissions in AISI 4140 steel are reported. The Barkhausen signal amplitude is known to be highly sensitive to the type and distribution of microstructural inhomogeneities, such as grain boundaries, precipitates and dislocations. The Barkhausen measurements were taken on samples having pearlitic, spheroidized and bainitic microstructures. The Barkhausen emissions were measured in terms of rms voltage, peak-to-peak voltage and number of events per cycle. It is shown that Barkhausen signals can be used to distinguish between pearlitic and bainitic microstructures. © 1995 IEEE

World University root node

IEEE Transactions on Magnetics

Influence of microstructure on micromagnetic barkhausen emissions in AISI 4140 steel

The amorphous Fe40 Ni40 B20 alloy shows excellent soft magnetic properties when heat-treated at 630 K for 10-15 min. The improved magnetic softness is attributed to the relaxation of internal stress. The relaxation behaviour obeys the so-called ‘In t’ kinetics. Small crystalline particles do appear after longer duration isothermal treatment at 630 K which is much lower than the crystallization temperature. Formation of crystalline particles induces magnetocrystalline anisotropy in the system which in turn detoriorates the magnetic softness. © 1994, The Japan Institute of Metals. All rights reserved.

Materials Transactions, JIM

Magnetic Behaviour of Amorphous Fe40Ni40B20 Ally Treated Isothermally below Crystallzation Temperature

Scripta Metallurgica et Materiala

The effect of near-crystallization temperature annealing on the electrochemical behavior of amorphous Fe77.5B15Si7.5 fibres in borate buffer

The effects of grain growth and compositional changes on the electrochemical behavior and the resistivity of amorphous iron-boron-silicon (Fe77.5B15Si7.5) alloys after crystallization were studied. Deterioration of the protective passive film was observed, along with increased annealing. Potentiodynamic polarization provided excellent information about microstructural and chemical changes. It was concluded that electrochemical measurements could be used in conjunction with resistivity measurements in direct studies of grain growth and chemical changes occurring in different phases of the devitrified alloy.

Corrosion

Polarization and resistivity measurements of post-crystallization changes in amorphous Fe-B-Si alloys

Magnetic properties of a hydrogenated amorphous Fe-Si-B fiber have been studied. Hydrogen was charged electrochemically. Saturation magnetization and the switching characteristics of the fiber have been investigated for different charging conditions. Saturation magnetization is found to decrease with the increase of charging time and charging current density. Variation of switching characteristics with the charging conditions is rather complex. Magnetic properties have also been studied during degassing of hydrogen. Hydrogen inside the specimen induces tensile stress due to volume expansion and at the same time modifies Fe-Fe exchange interaction. The magnetic behavior due to hydrogenation and during degassing have been explained by considering the dual role of hydrogen inside the fiber.

Fulltext

Journal of Applied Physics

Magnetic properties of hydrogenated amorphous Fe-Si-B fiber

The magnetic response and the behavior of the harmonic components of a bulk sample of the superconducting composite system YBa2Cu3O7-:Ag0.1 are studied in the presence of a varying sinusoidal magnetic field. It is observed that as the amplitude of the field increases, the wave form of the magnetization M changes from a nearly sinusoidal, to a square-wave-like, then to a two-peak structure, consistent with the prediction of critical-state models. The crossover from the Bean to Anderson-Kim regime is found in the amplitude dependence of the third- and fifth-harmonic response at a fixed temperature. The third-harmonic response shows a peak below Tc as the sample is cooled and the peak shifts to lower temperature and broadens with increasing amplitude of the exciting field. The second-harmonic response, which is zero in the absence of a dc field, passes through a maximum as the dc field is increased. The results of these measurements are in agreement with predictions of the modified critical-state model that incorporates the field dependence of the critical current. © 1992 The American Physical Society.

Physical Review B

Magnetization and harmonic response of YBa2Cu3O7-:Ag composites

The crystallization in amorphous Fe40Ni40B20 alloy has been studied by electrical resistivity measurement. It shows a three stage compared to the more conventional two-stage crystallization behaviour in many metallic glasses. The Johnson-Mehl-Avrami equation was found to be operative only for 40% transformed crystallized volume for the highest measured isotherm (740 K). The Avrami exponent and activation energy were found to be 1.75 and 53 kcal mol-1, respectively. The low activation energy in the amorphous alloy has been explained by the structural relaxation model. © 1992 Chapman &amp; Hall.

Journal of Materials Science

Crystallization study of amorphous Fe40Ni40B20 by electrical resistivity measurement

A simple fluxgate magnetometer is developed using low magnetostrictive ferromagnetic amorphous alloy acting as a sensing element. It uses the fact that the magnetization of sensing element symmetrically magnetized by a sinusoidal field contains even harmonic components in presence of dc signal field H and the amplitude of the second harmonic component of magnetization is proportional to H. The sensitivity and linearity of the magnetometer with signal field are studied for parallel configuration and the field ranging from 10 nT to 10 μT can be measured. The functioning of the magnetometer is demonstrated by studying the shielding and flux-trapping phenomena in high-Tc superconductor. © 1992.

Journal of Magnetism and Magnetic Materials

A simple fluxgate magnetometer using amorphous alloys

The magnetization of a polycrystalline composite YBa2Cu3O7-x:Ag0.1 in the superconducting state is measured in the presence of a small a.c. magnetic field. With increase in field amplitude, the magnetization M(t) changes its shape from nearly sinusoidal to square-wave like and then to a two-peak structure. A similar behavior of the magnetization M(t), calculated from the critical-state model with intergranular critical current Jc=αc[μ(H0+|H|)]-1 is obtained. A very good fit is found between the theoretical and experimental results, and the parameters of the model are estimated. © 1992 Plenum Publishing Corporation.

Journal of Superconductivity

Magnetic behavior of weak links in bulk superconducting YBa2Cu3O7-x: Ag composite

The harmonic responses of the magnetic induction of a superconducting YBa2Cu3O7-x:Ag0.1 composite at 77 K were measured as a function of the amplitudes of the exciting AC fields and the biasing DC fields. The odd harmonic responses of the zero-field cooled sample exhibit oscillatory nature with increase in the biasing field. The hysteresis of these responses due to the cycling of the biasing field shows a 'butterfly'-like structure at low excitation and more complex behavior at higher levels of exciting field. The hysteresis effects are discussed qualitatively in terms of the trapped flux and critical state model.