Papers by Keyword: High Magnetic Field

Abstract: The effect of a 6T high magnetic field on the microstructure of directionally solidified NiAl-Cr (Mo)-Si near-eutectic alloy was investigated at the withdrawal rates of 2, 10 and 50 μm/s. The results showed that the microstructure evolved from planar eutectic to primary NiAl dendrites + cellular eutectic and then to dendritic eutectic with the increasing withdrawal rate. When the magnetic field was imposed, the well-aligned eutectic lamellae were disturbed and transformed into a wavy one at 2 μm/s. When the withdrawal rate increased to 10 μm/s, the application of the magnetic field destroyed the primary NiAl dendrite array and caused the occurrence of columnar-to-equiaxed transition (CET) of the NiAl dendrites. The volume fraction of primary dendrites also decreased. In addition, the width of intercellular/interdendritic regions decreased in cellular/dendritic eutectic structures when directionally solidified under the magnetic field. The above results should be attributed to the combined action of the thermoelectric magnetic force and the thermoelectric magnetic convection.

Abstract: In the TC4 titanium alloy subject to high pulsed magnetic field, the phase transformation from α to β occurs. When the magnetic induced intensity increased from 2T, 3T to 4T with constant 30 pulses, the percent of α phase adds up gradually. When the magnetic induced intensity is 4T the volume fraction of α phase amounts up to 59%. It is ascertained that magnetic field has taken a positive influence on the phase transformation because of the variation of inner energy induced by magnetic field.

Abstract: Nanometer Al₂O₃ particles reinforced 7055Al composites were processed by high magnetic field with 2T,3T and 4T magnetic induced intensity (B) with constant 30 pulses. Transmission Electronic Microscopy (TEM) and X ray diffraction (XRD) were mainly used to analyze some characteristic of the treated samples. The results show that with the increase of B the dislocation density was enhanced apparently. It is deduced that plastic deformation was the main reason of high density dislocation. The magnetoplasticity effect was the source of plastic deformation.

Abstract: The evolutions of mechanical properties and microstructure of cryoECAPed 1050 alloy annealed at various temperatures from 150°C to 400°C for 1h with and without high magnetic field (HMF) were investigated by hardness test and electron back scattering diffraction pattern (EBSD) analysis. The abnormal grain growth happens in sample annealing at 400°C without a field. With the application of high magnetic field, the formation of the HABs is suppressed, the grain size distribution is homogeneous and no abnormal grain growth occurs.

Abstract: The surface tension of water in high magnetic fields up to 10T was investigated with aid of the high-magnetic-field tensiometer (HMFT). It was found that the surface tension of water linearly varied with the magnetic field intensity and increased by 0.48mN/m or 0.65% in 10T. The increase of the surface tension of water could be attributed to the increase in the number and stabilization of the hydrogen bonds in the magnetic field.

Abstract: The property and microstructure of pure Al prepared by the cryogenic ECAP after annealing at different temperatures and times with and without the application of 12T high magnetic field were investigated by hardness test and optical microscopy observation. The results show that with the application of high magnetic field, the hardness of cryo-ECAPed pure Al is lower than that of material annealing without high magnetic field. The high magnetic field accelerates crystallization of cryo-ECAPed pure Al during annealing.

Abstract: Various textured alumina ceramics were prepared by colloidal processing in high magnetic field and heating from alumina powder as raw material in this study. The effects of the magnetic field strength, heating time and heating temperature on the particle orientation were systematically examined for these samples with scanning electron microscope (SEM) and X-ray diffraction (XRD) etc. The experimental results showed that alumina grains are polyhedral ball shape of, no textured structure exists in the sintered bodies without magnetic field treatment; the alumina grains align with the c-axis parallel the magnetic field direction under high magnetic field, the grains present strip shape in the sintered alumina bodies with the magnetic field treatment; the particle orientation degree increases with increasing the heating time and heating temperature; when the sintering temperature achieves about 1823K, the textured microstructure can be obviously observed in the sintered alumina bodies.

Abstract: The present studies are to investigate the microstructure features and macroscopical hardness during transformation from austenite to pearlite without and with 12T magnetic field on Fe-1.1%C alloy. It is found that 12T magnetic field can increase the area fraction of abnormal microstructure and the average width of secondary cementite in Fe-1.1%C alloy by remarkably decreasing the Gibbs energy needed for the ferrite transformation. The macroscopical hardness of the specimens heated with 12Tmagnetic field is lower than the specimens without magnetic field. The reason is that the magnetric field increase the lamellar spacing of pearlite

Abstract: A gradient high magnetic field effected significantly the morphology and distribution of the primary silicon grains in Al-18Si alloy. Experimental studies shew that in the gradient high magnetic field the primary silicon phase grains, which are large plate-like or five-star-like in the case of solidification without magnetic field, are accumulated on the top of the specimen and refined remarkably with the morphology of polygonal or nodular shapes when the alloy solidifies from the semisolid state. In the segregated layer of the silicon, the distribution of the silicon grains is homogeneous. The size of the primary silicon grains decreases and the grain number density rises with the increase of the magnetic strength maintaining the magnetization force unchangeable. It seems that the high magnetic field influences the diffusion of silicon. Theoretical models have been proposed to explain the refining and the distribution of the silicon grains.

Abstract: To investigate the effect of high magnetic fields on the solidification behavior of binary eutectic system, solidification and quenching experiments of Al-11.8 wt.%Si and Ag-10 wt.%Cu alloys were carried out with and without an 8.8 T high magnetic field. It was found that the application of the high magnetic field could increase the concentration of Si in the primary Al and Cu in the primary Ag at their eutectic temperatures, but could not obviously affect the Si concentration in the primary Al at room temperature. The above increase can be attributed to the weakness of the solute diffusion at the liquid-solid interface during solidification caused by the high magnetic field.