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H Kikuchi - One of the best experts on this subject based on the ideXlab platform.
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magnetic evaluation of irradiation hardening in a533b reactor pressure vessel steels magnetic hysteresis measurements and the model analysis
Journal of Nuclear Materials, 2012Co-Authors: S Kobayashi, H Kikuchi, T Yamamoto, D Klingensmith, G R Odette, Yasuhiro KamadaAbstract:Abstract We report results of measurements of magnetic Minor hysteresis Loops for neutron-irradiated A533B nuclear reactor pressure vessel steels varying alloy composition and irradiation condition. A Minor-Loop coefficient, which is obtained from a scaling power law between Minor-Loop parameters exhibits a steep decrease just after irradiation, followed by a maximum in the intermediate fluence regime for most alloys. A model analysis assuming Avrami-type growth for Cu-rich precipitates and an empirical logarithmic law for relaxation of residual stress demonstrates that an increment of the coefficient due to Cu-rich precipitates increases with Cu and Ni contents and is in proportion to a yield stress change, which is related to irradiation hardening.
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low field magnetic characterization of ferromagnets using a Minor Loop scaling law
Journal of Applied Physics, 2010Co-Authors: Satoru Kobayashi, Yasuhiro Kamada, Seiki Takahashi, Toetsu Shishido, H KikuchiAbstract:A scaling power law relating hysteresis loss and remanence in Minor hysteresis Loops is proposed for the low-field magnetic characterization of ferromagnetic materials. We demonstrate that the law holds true for very low to an intermediate level of magnetization, associated with a universal exponent of ≈1.35, irrespective of types of ferromagnets and temperature, unlike the Steinmetz law with limited applicability. The coefficient in the scaling law shows almost the same behavior as coercivity and can be used for the evaluation of the magnetic quality of materials for which the Steinmetz law cannot be applied and/or low measurement field is necessary.
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quantitative evaluation of dislocation density using Minor Loop scaling relations
Journal of Magnetism and Magnetic Materials, 2008Co-Authors: S Kobayashi, T Kimura, S Takahashi, Yasuhiro Kamada, H KikuchiAbstract:Abstract Relationships between Minor hysteresis Loops and dislocation density have been investigated at various temperatures from 10 to 600 K in polycrystalline nickel with tensile deformation. It was revealed that coefficients obtained from scaling relations between parameters of Minor-Loops are in linear proportion to stress at all measuring temperatures below its Curie temperature. Considering that dislocation density is generally in proportion to the square root of true stress, it is concluded that the coefficients are related with the square root of dislocation density. This method using Minor hysteresis Loops is useful for quantitative evaluation of dislocation density because of its very low measurement field.
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relationship between mechanical and magnetic properties in cold rolled low carbon steel
Journal of Applied Physics, 2006Co-Authors: S Takahashi, H Kikuchi, Satoru Kobayashi, Y KamadaAbstract:Structure-sensitive properties of Minor hysteresis Loops have been compared with Vickers hardness and ductile-brittle transition temperature (DBTT) obtained by Charpy impact test for cold rolled low carbon steel. Minor Loops were measured with increasing magnetic field amplitude, step by step, and were analyzed in connection with the rolling reduction. We found that Minor-Loop coefficients deduced from relations between Minor-Loop parameters increase with increasing rolling reduction and have a simple relationship with both mechanical properties, Vickers hardness, and DBTT. We also found that these coefficients have a linear relation with coercive force obtained by the major Loop. The present analysis method using Minor Loops is highly effective for nondestructive evaluation of ductile-brittle transition, in terms of the high sensitivity to lattice defects as well as low measurement field.
S Takahashi - One of the best experts on this subject based on the ideXlab platform.
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Domain-Wall Pinning in Er and Dy Studied by Minor-Loop Scaling Laws
Journal of Physics: Conference Series, 2011Co-Authors: S Kobayashi, S Takahashi, Hiroaki Kikuchi, Yasuhiro KamadaAbstract:Scaling laws of magnetic Minor hysteresis Loops for heavy rare-earth metals Er and Dy were studied. We found that there exists a scaling power law between hysteresis loss and remanence of Minor Loops with a constant exponent of 1.2–1.3 in the low-temperature ferromagnetic phase below Tc as was commonly observed in soft ferromagnetic materials. However, the scaling law persists even in the higher temperature incommensurate antiferromagnetic phase with no net spontaneous magnetization. These observations reflect the irreversible movement of Bloch walls, which separate ferromagnetic domains below Tc or small ferromagnetic regions in the antiferromagnetic phase.
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Analysis of Magnetic Minor Hysteresis Loops in Thermally Aged and Cold-rolled Fe-Cu Alloys
Journal of Physics: Conference Series, 2011Co-Authors: F Takahashi, S Kobayashi, S Takahashi, Yasuhiro Kamada, T Murakami, Hiroaki KikuchiAbstract:Neutron irradiation causes the formation of Cu precipitate in reactor pressure vessel steel and makes the steel susceptible to rupture. In the present study, we have examined magnetic Minor hysteresis Loops of Fe-1wt%Cu alloy after thermally ageing at 753 K and subsequent cold rolling to elucidate the effects of Cu precipitation on magnetic properties. Minor-Loop coefficients, obtained from scaling power laws between field-dependent parameters of Minor hysteresis Loops, decrease with ageing time and show a local maximum around 200 min, reflecting the growth of Cu precipitates with ageing. For the alloy cold-rolled after ageing, the Minor-Loop properties linearly increase with reduction and show a good relationship with mechanical properties such as DBTT and hardness. These observations indicate that the analysis method using magnetic Minor Loops can be an useful technique of nondestructive evaluation of irradiation embrittlement and subsequent deformation hardening in reactor pressure vessel steels.
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The effect of copper and manganese on magnetic Minor hysteresis Loops in neutron irradiated Fe model alloys
Journal of Nuclear Materials, 2009Co-Authors: Satoru Kobayashi, S Takahashi, Yasuhiro Kamada, D Klingensmith, Hiroaki Kikuchi, Takuya Yamamoto, G R OdetteAbstract:Abstract Changes of magnetic Minor hysteresis Loops in pure Fe, Fe–1 wt% Mn, Fe–0.9 wt% Cu, and Fe–0.9 wt% Cu–1 wt% Mn model alloys after neutron irradiation have been studied. Minor-Loop coefficients which are obtained from scaling relations between Minor-Loop parameters and in proportion to internal stress, were found to decrease in all model alloys after the irradiation to a fluence of 3.32 × 1019 n cm−2. The decrease of the coefficients is larger for alloys including Cu and is enhanced by 1 wt% Mn addition. Such decrease implying the reduction of internal stress during irradiation is in contrast with changes of yield strength after the irradiation that increase with Cu and Mn contents. A qualitative explanation was given on the basis of the preferential formation of Cu precipitates along pre-existing dislocations which reduces internal stress of the dislocations.
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quantitative evaluation of dislocation density using Minor Loop scaling relations
Journal of Magnetism and Magnetic Materials, 2008Co-Authors: S Kobayashi, T Kimura, S Takahashi, Yasuhiro Kamada, H KikuchiAbstract:Abstract Relationships between Minor hysteresis Loops and dislocation density have been investigated at various temperatures from 10 to 600 K in polycrystalline nickel with tensile deformation. It was revealed that coefficients obtained from scaling relations between parameters of Minor-Loops are in linear proportion to stress at all measuring temperatures below its Curie temperature. Considering that dislocation density is generally in proportion to the square root of true stress, it is concluded that the coefficients are related with the square root of dislocation density. This method using Minor hysteresis Loops is useful for quantitative evaluation of dislocation density because of its very low measurement field.
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relationship between mechanical and magnetic properties in cold rolled low carbon steel
Journal of Applied Physics, 2006Co-Authors: S Takahashi, H Kikuchi, Satoru Kobayashi, Y KamadaAbstract:Structure-sensitive properties of Minor hysteresis Loops have been compared with Vickers hardness and ductile-brittle transition temperature (DBTT) obtained by Charpy impact test for cold rolled low carbon steel. Minor Loops were measured with increasing magnetic field amplitude, step by step, and were analyzed in connection with the rolling reduction. We found that Minor-Loop coefficients deduced from relations between Minor-Loop parameters increase with increasing rolling reduction and have a simple relationship with both mechanical properties, Vickers hardness, and DBTT. We also found that these coefficients have a linear relation with coercive force obtained by the major Loop. The present analysis method using Minor Loops is highly effective for nondestructive evaluation of ductile-brittle transition, in terms of the high sensitivity to lattice defects as well as low measurement field.
Yuzuru Hosoe - One of the best experts on this subject based on the ideXlab platform.
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designing magnetics of capped perpendicular media with Minor Loop analysis
Journal of Magnetism and Magnetic Materials, 2008Co-Authors: Hiroaki Nemoto, I Takekuma, Hiroyuki Nakagawa, Takayuki Ichihara, R Araki, Yuzuru HosoeAbstract:A novel method of analyzing the switching field distribution (SFD) and magnetic correlation length of perpendicular magnetic recording media that uses major and Minor magnetization Loops is proposed. By applying the analysis to a series of capped perpendicular media, we found that a thick capping layer with a low saturation magnetization effectively reduced SFD without rapidly increasing the magnetic correlation length. Transmission electron microscope observation suggests that the SFD is narrowed by the increased uniformity of intergranular exchange coupling via the thick capping layer. Evaluations of recording characteristics demonstrated a close correlation between narrower SFDs and improved recording performance. Reducing exchange coupling dispersion is a clear solution for improving the performance of recording media.
Satoru Kobayashi - One of the best experts on this subject based on the ideXlab platform.
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Effects of high-strain-rate deformation on magnetic hysteresis in high-tensile steels
AIP Advances, 2016Co-Authors: Ryo Morita, Satoru Kobayashi, Akindele Odeshi, Jerzy A. Szpunar, Kodai Miura, Yasuhiro KamadaAbstract:We have studied a relationship between magnetic hysteresis and microstructures on high-tensile AISI 4340 steels after impact loading with a strain rate up to 2100 s−1 We find that coercivity, and Minor-Loop coefficient which is deduced from a power-law scaling between Minor-Loop parameters increase with strain rate, show a maximum at around a strain rate of 1400 s−1, followed by a decrease at a higher strain rate, associated with magnetic anisotropy with respect to impact direction. These observations are explained from the viewpoints of heat generation and heterogeneous microstructures characteristic to steels subjected to high strain rate deformation.
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low field magnetic characterization of ferromagnets using a Minor Loop scaling law
Journal of Applied Physics, 2010Co-Authors: Satoru Kobayashi, Yasuhiro Kamada, Seiki Takahashi, Toetsu Shishido, H KikuchiAbstract:A scaling power law relating hysteresis loss and remanence in Minor hysteresis Loops is proposed for the low-field magnetic characterization of ferromagnetic materials. We demonstrate that the law holds true for very low to an intermediate level of magnetization, associated with a universal exponent of ≈1.35, irrespective of types of ferromagnets and temperature, unlike the Steinmetz law with limited applicability. The coefficient in the scaling law shows almost the same behavior as coercivity and can be used for the evaluation of the magnetic quality of materials for which the Steinmetz law cannot be applied and/or low measurement field is necessary.
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The effect of copper and manganese on magnetic Minor hysteresis Loops in neutron irradiated Fe model alloys
Journal of Nuclear Materials, 2009Co-Authors: Satoru Kobayashi, S Takahashi, Yasuhiro Kamada, D Klingensmith, Hiroaki Kikuchi, Takuya Yamamoto, G R OdetteAbstract:Abstract Changes of magnetic Minor hysteresis Loops in pure Fe, Fe–1 wt% Mn, Fe–0.9 wt% Cu, and Fe–0.9 wt% Cu–1 wt% Mn model alloys after neutron irradiation have been studied. Minor-Loop coefficients which are obtained from scaling relations between Minor-Loop parameters and in proportion to internal stress, were found to decrease in all model alloys after the irradiation to a fluence of 3.32 × 1019 n cm−2. The decrease of the coefficients is larger for alloys including Cu and is enhanced by 1 wt% Mn addition. Such decrease implying the reduction of internal stress during irradiation is in contrast with changes of yield strength after the irradiation that increase with Cu and Mn contents. A qualitative explanation was given on the basis of the preferential formation of Cu precipitates along pre-existing dislocations which reduces internal stress of the dislocations.
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A scaling power-law relation in magnetic Minor hysteresis Loops in Fe and Ni metals
Journal of Physics: Condensed Matter, 2007Co-Authors: Seiki Takahashi, Satoru Kobayashi, Toetsu ShishidoAbstract:A simple scaling relationship has been found in the limited amplitude range of quasistatic Minor hysteresis Loops: Wa* = Wa0(Ma*/Ms)n, where Wa* is the area enclosed by the Minor hysteresis curve and Minor-Loop magnetization Ma* in the first quadrant. Wa* is related to the energy dissipated during the restoration process of domain walls toward the zero applied field state. Ms is the saturation magnetization and n has a constant value of about 1.0, being independent of ferromagnets, temperature, and lattice defects such as dislocations. The Minor-Loop effluence coefficient Wa0 has information on microstructure and shows a simple linear relation to the applied stress. The dependence of Wa0 on applied stress and temperature can be explained by use of magneto-striction constants, the magneto-crystalline anisotropy, and electrical conductivity.
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relationship between mechanical and magnetic properties in cold rolled low carbon steel
Journal of Applied Physics, 2006Co-Authors: S Takahashi, H Kikuchi, Satoru Kobayashi, Y KamadaAbstract:Structure-sensitive properties of Minor hysteresis Loops have been compared with Vickers hardness and ductile-brittle transition temperature (DBTT) obtained by Charpy impact test for cold rolled low carbon steel. Minor Loops were measured with increasing magnetic field amplitude, step by step, and were analyzed in connection with the rolling reduction. We found that Minor-Loop coefficients deduced from relations between Minor-Loop parameters increase with increasing rolling reduction and have a simple relationship with both mechanical properties, Vickers hardness, and DBTT. We also found that these coefficients have a linear relation with coercive force obtained by the major Loop. The present analysis method using Minor Loops is highly effective for nondestructive evaluation of ductile-brittle transition, in terms of the high sensitivity to lattice defects as well as low measurement field.
Hiroaki Nemoto - One of the best experts on this subject based on the ideXlab platform.
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Incoherent Switching Amount Analysis of Exchange Spring Media by Using Initial Minor Loop Slope Measurement
IEEE Transactions on Magnetics, 2010Co-Authors: Yoshihiro Ikeda, Gunn Choe, S. H. Florez, Hiroaki Nemoto, B. Lengsfield, K. TakanoAbstract:We describe a newly developed initial Minor Loop slope (IMLS) experimental method capable of measuring reversal switching in exchange spring perpendicular media. The slope peak height is centered near the medium's coercivity Hc. The magnitude of the peak signal is correlated with the soft top (cap) layer's moment, Mst, and the exchange coupling strength between the cap and hard magnetic oxide layers. The peak position was correlated to the media Hc for media that is thermally stable and migrates to smaller fields in less stable media. The IMLS results are compared with both remanent angular dependence coercivity, Hcr, measurements and micro-magnetic simulations. This technique provides a simple method of characterizing incoherent switching behavior in different types of exchange spring media.
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designing magnetics of capped perpendicular media with Minor Loop analysis
Journal of Magnetism and Magnetic Materials, 2008Co-Authors: Hiroaki Nemoto, I Takekuma, Hiroyuki Nakagawa, Takayuki Ichihara, R Araki, Yuzuru HosoeAbstract:A novel method of analyzing the switching field distribution (SFD) and magnetic correlation length of perpendicular magnetic recording media that uses major and Minor magnetization Loops is proposed. By applying the analysis to a series of capped perpendicular media, we found that a thick capping layer with a low saturation magnetization effectively reduced SFD without rapidly increasing the magnetic correlation length. Transmission electron microscope observation suggests that the SFD is narrowed by the increased uniformity of intergranular exchange coupling via the thick capping layer. Evaluations of recording characteristics demonstrated a close correlation between narrower SFDs and improved recording performance. Reducing exchange coupling dispersion is a clear solution for improving the performance of recording media.