Papers by Keyword: High Magnetic Field

Abstract: The present studies are to investigate the microstructure features during transformation from austenite to ferrite without and with magnetic field on Fe-0.76%C alloy. It is found that the area fraction and numbers of proeutectoid ferrite grain as well as the lamellar spacing of pearlite in Fe-0.76%C alloy increased considerably with the increase of magnetic field intensity. The reason is that, the magnetic field increases the driving force of proeutectoid ferrite nuclei and shifts the eutectoid point to the side of high carbon content and high temperature, which increases the starting-temperature of the transformation from austenite to ferrite. The proeutectoid ferrite grains are elongated along the magnetic field direction, which can be explained as follows: the proeutectoid ferrite becomes the magnetic dipolar under high magnetic field, and then the polarized austenite atoms are much easier to diffuse into ferrite grains along the magnetic field direction. Key words: high magnetic field; Fe-0.76%C alloy; microstructure

Abstract: The Mg₂NiH₄ hydrogen storage material was successfully prepared by controlled hydriding combustion synthesis (CHCS) from Mg and Ni powders in a high magnetic field. The effects of magnetic intensity on the structure, phase compositions and the hydriding/dehydriding (A/D) properties of the composite are investigated. As a result, a high magnetic field promotes the formation of Mg₂NiH₄. The PCT results show that the maximal hydrogen capacity at 573 K is 3.59 wt.%. The comparison of the hydrogen A/D results under the different conditions suggested that 4 T is the optimal magnetic intensity in our trial.

Abstract: The effect of magnetic field on diffusion behavior of carbon in pure iron was investigated. The results showed that the magnetic field can accelerate the carbon diffusion when the magnetic field direction is perpendicular to the carburized direction, and this effect increases with the enhancement of magnetic field intensity.

Abstract: Sheets of cold rolled (76%) IF steel were annealed at 650°C for 30min under a 12-tesla magnetic field. During the magnetic field annealing, they were placed at the center of the applied field respectively, being oriented differently with respect to the magnetic field direction. The results show that the high magnetic field annealing prevents the evolution from deformed {111}<110> texture component to recrystallized {111}<112> texture component at the initial stage of recrystallization. For the field annealed specimens, altering the specimen orientation to the magnetic field direction during annealing does not change the final annealing textures. The intensity of main {111} texture components presents a similar periodic variation with respect to the specimen orientation to the magnetic field.

Abstract: Aging treatment of Cu-17Fe alloy was investigated by a vacuum heat treating furnace in high magnetic furnace. The microstructures were documented using scanning electron microscopy (SEM). The solid solubility of Fe in Cu matrix was analysed by energy spectrometer (EDS). The mechanical properties were measured with a Vickers hardness tester. The electrical conductivity was measured with a micro-ohmmeter. The results showed that high magnetic field can promote spheroidization of the Fe dendrites, the spheroidization intensifies and the solid solubility decreases with the increasing magnetic induction intensity of the high magnetic field exerted to the alloy, the solid solubility of Fe is minimum when the magnetic induction intensity is 10T at 500°C during precipitation. And Cu-17Fe alloy has a good strength/conductivity combination of 110Hv/63%IACS after aging treatment of 10T at 500°C for 1h.

Abstract: The microstructural evolutions of 7055 aluminum alloy after single and two-step homogenization with or without applying 12T high magnetic field were investigated. The as-cast microstructures of 7055 alloy consist of α+AlZnMgCu eutectics, Al7Cu2Fe phase and AlTiCuFe phase. During homogenization, coarse α+AlZnMgCu eutectics located at interdendritic region become smaller, discontinuous and spheroidized, some of them transform into Al2CuMg (S) having a higher melting point. High magnetic field significantly accelerates the dissolution of α+AlZnMgCu eutectics and S phase. The least amount of α+AlZnMgCu eutectics and S phase is obtained when the alloy homogenized at 4650C/10h+4850C/8h under 12T high magnetic field.

Abstract: The effect of a high magnetic field (up to 12T) on the lamellar eutectic spacing changes was investigated in the diffusion liquid Al/solid Cu. It was found that the lamellar eutectic alloy is formed in the diffusion process and its spacing has the non-monotonic relationship with the magnetic field intensity. With the increase of magnetic field intensity, the lamellar eutectic spacing decreases rapidly. When the magnetic field intensity B exceeds 4T, the lamellar eutectic spacing begins to increase until 8T, and then, decrease again. This phenomenon could be attributed to the effects of high magnetic fields suppressing nature convection and inducing thermo-electromagnetic convection in the liquid Al.

Abstract: Those materials with an one dimensional phase-aligned structure have a large amount of potentiality as engineering materials because of their exceptional optical, electrical and anisotropically mechanical properties. Many researchers are now working determinedly to explore the methods for fabricating this kind of material. Recently, high magnetic fields have been used to fabricate non-magnetic materials with textured structure where anisotropic magnetic energy should be strong enough to induce preferred crystal orientation. Based on this mechanism, we developed an in situ process for fabricating phase-aligned composites using high magnetic fields. In this work, hypoeutectic Mn-Sb and hypereutectic Al-Ni alloys were solidified in various magnetic fields. The primary MnSb dendrites in the solidified Mn-Sb alloys were found to be macrostructurally aligned along the field direction, while the primary Al3Ni phases in the Al-Ni alloys were found to be macrostructurally aligned perpendicular to the field direction. The X-ray diffraction (XRD) measurement results suggested that these two phases were also oriented by the magnetic field. It was believed that the above-mentioned alignment is based on the crystal orientation and relevant to the heat flux direction, the preferred growth direction and the concentration field around crystallized crystals.

Abstract: The effect of high magnetic field annealing on the nucleation sites for recrystallized nuclei with {111}<112> orientation in the initial stage of recrystallization in as-annealed interstitial-free (IF) steel sheet were investigated by the SEM-EBSD analysis. Specimens of cold rolled IF steel sheet were annealed at 650°C for 0min and 10min respectively with a 12-tesla magnetic field to obtain a partially recrystallized microstructure. During the magnetic field annealing, they were respectively placed at the center of the applied field with their rolling planes parallel to the magnetic field direction (MD), and with their rolling direction (RD) parallel and normal to the MD, respectively. It was found that different to the non-field annealed specimen, in the field annealed specimens, the {111}<112> oriented recrystallized nulei favored to nucleate in the {111}<112> deformed matrix and not in the {111}<110> deformed matrix. This phenomenon may be attributed to the magnetic ordered state induced by the magnetic field, which might suppress the formation of high-energy grain boundaries between the newly formed nuclei and the deformed matrix.

Abstract: Recently, we have developed crystal-oriented sheet forming (COSF) process from green sheet process and high-magnetic-field method. We formed c-axis-oriented (Sr,Ca)2NaNb5O15 (SCNN) sheets by the COSF process, and succeeded in realizing c-axis-oriented single-plate type piezoelectric ceramics (O-SP) and c-axis-oriented multilayered type piezoelectric ceramics (O-MLPC) for SCNN. From the measurement results of displacement induced by electric field, it was clarified that effective d33 of the O-SP was 210~240 pm/V. This value was about 3 times larger than that of the randomly oriented single-plate type, which was 70% of that of single crystal. Moreover, it was confirmed that O-MLPC indicated displacements 2.5 times as large as that of the conventional multilayer piezoelectric ceramics. In this study, we clarified that piezoelectric properties in bulk and multilayer structure can be drastically enhanced using the COSF process.