Effect of Longitudinal Magnetic Field on Microstructures of Directionally Solidified Ni-Based Superalloy

The effect of a longitudinal static magnetic field on the microstructures of the superalloy DZ417G during directional solidification at the low withdrawal velocity was investigated experimentally.The experimental results showed that the application of a high static magnetic field significantly changed the interface shapes and microstructures of the superalloy.In practice,when the magnetic filed is applied,the well-ordered columnar dendrite structures still existed in the entire sample as the increase of magnetic field from 0 to 0.3 T.With the increase of magnetic field,the columnar to equiaxed transition(CET)occurred and reaches a maximum under a 0.5 T magnetic filed,and then decrease with the magnetic filed still increase.When the magnetic field is higher than 1.2 T,equiaxed grains zone on the edge of sample increased again and gradually extended from the edge to the center of the sample.Moreover,the macrosegregation may occur along with the appearance of the equiaxed grains.These phenomena should be contributed to interaction of the EMD and TEMC in liquid phase and TEMF in solid phase.     

Effect of Electromagnetic Stirring on Fine Grain Formation and Tensile Property Improvement for Fe-Ni Superalloy

Due to its excellent creep rupture strength and low cost,superalloy GH2984 has becoming a promising material to be used as heat exchanger in the prospective 700℃fossil power plant.The mechanical strength,which is a particularly important indicator for the superalloy,strongly depends on the grain size and crabide distribution.In current study,we have investigated the influence of a rotating magnetic field(RMF)on the solidified microstructures and tensile properties of superalloy GH2984.RMF has been applied to provide a forced convection within the solidifying melt.The melt stirring by a sufficiently high magnetic field provides homogeneous grain size and elements distribution in the sample volume.Meanwhile,yield strength is found to be effectively enhanced for the sample solidified under magnetic field.The result has demonstrated that the RMF method on the melt solidification process shows a promising perspective for refining the grains and promoting the mechanical strength of superalloy GH2984.     

Columnar-to-Equiaxed Transition During Directional Solidification Under Strong Magnetic Field

Effects of strong magnetic fields on the columnar-to-equiaxed transition(CET)have been investigated experimentally.Experimental results show that the application of a strong magnetic field causes a dendrite fragmentation and then the CET.The thermoelectric magnetic force acting on cells/dendrites and equiaxed grains in the mushy zone has been studied numerically.Numerical results reveal that a torque is created on cells/dendrites and equiaxed grains and the value of the thermoelectric magnetic force increases as the magnetic field intensity increase.This torque breaks cells/dendrites and drives the rotation of equiaxed grains.As a consequence,the CET will occur during directional solidification under a strong magnetic field.This may initiate a new method to induce the CET via an applied strong magnetic field during directional solidification.     

Effect of Electromagnetic Stirring on Solidification Structure of Incoloy 825 Superalloy

Superalloy Inconel 825 has been extensively used in chemical industry and transportation industry due to its excellent creep rupture strength and prominent corrosion resistant properties under various circumstances.However,the mass production of this alloy by continuous casting method is restricted because of the serious macrosegregation and coarse grains in the billet.In current,a linear travelling magnetic field was introduced in the solidification process of Inconel 825 with the aim of changing the fmal microstructure by electromagnetic stirring(EMS)force.The results have indicated that the dendrite structure of Incoloy 825 is refined obviously with applying EMS,and the mechanism of dendrite refinement is presumed to the introduction of a forced convection within the solidifying melt.Moreover,The number and the size of precipitated phases including carbide and nitride were found to be significantly reduced with EMS,a phenomenon on the reduction of interdendritic segregation of titanium and molybdenum was simultaneously observed,which demonstrated that he release of interdendritic segregation by EMS inhibits the growth dynamic of carbide and nitride from the melt.     

The Sensitivity to Axial Alignment of a Flow Driven by a Travelling Magnetic Field

The present study,both experimentally and by numerical simulation,concerns the sensitivity of a flow that is driven by a travelling magnetic field(TMF)with respect to a stepwise applied mismatch between the axes of the TMF and of the cylindrical liquid metal column.The TMF is generated by six equidistantly arranged cylindrical coils powered with an AC current having a phase shift of 60℃between them.Because the flow induced by a TMF is basically of a toms type,vertical velocity components are representative for the motion in the meridional plane.Ultrasound Doppler Velocimetry(UDV)was applied to acquire the velocity component along the beam axis in the centre of the liquid metal column and at various azimuthal positions for a fixed radial coordinate.The measurements are compared to the flow data gained by large eddy simulations.Computations were based on the usual approximations to simplify the magnetohydrodynamic equations,which are low frequency and low induction,and on an analytical expression for the Lorentz force considering the shift between the fluid volume and the field.The results show that even a small shift between the axes may result in a distinct three-dimensional constituent of the flow structure which changes completely the usually assumed axisymmetric toms-type flow.     

Effect of Electromagnetic Frequency on Magnetic Flux Coupling by Traveling Magnetic Field

The effect of frequency on magnetic flux coupling field were analyzed with traveling-wave electromagnetic stirring system using a coupled model of magnetic induction and fluid dynamics.Simulations were performed to investigate the influences of the frequency on magnetic flux density,electromagnetic body force and flow field.The results showed that the magnetic flux density decreased with increasing frequency.The electromagnetic body force wavy moved along the same direction and increased with increasing the frequency when the traveling magnetic field is applied.The core area of the stirring was in the bottom of the alloy melt.A large circulation in the vertical section of the alloy melt can be produced by the electromagnetic body and the maximum flow rate first increased and then decreased with increasing frequency.     

Experimental evidence of magnetic training effect of electronic phase in Nd-Ca half-doped manganite

Cooling and heating modes are shown to be able to significantly modify the magnetic and electrical properties of the half-doped perovskite manganite.The present paper reports on a precise investigation of this phenomenon(the so-called training effect) carried out on Nd_(0.5)Ca_(0.5)MnO_3 manganite,which allow a fine tuning of the magnetic ground state.Refinement of the X-ray diffraction pattern shows that the synthesized sample is single phase and crystallizes in the orthorhombic structure with Pnma space group.Using magnetometry measurements,we have found that the sample is the seat of interesting phenomena like charge ordering,magnetic phase separation,spin-glass and inverse magnetocaloric effect.Magnetic-field-driven magnetization(M(μ_0 H)) measurements evidence the metamagnetic transition which not only depends on field value,but also on the thermal process(cooling or heating).Metamagnetic irreversibility in the magnetic field range(±5 T) and memory effect are observed at low temperatures due to the kinetic arrest phenomenon.It is worthwhile to mention that the coercive field increases with decreasing temperature and reaches 955 Oe at 20 K,which is sufficiently large compared with that one in the soft magnetic and makes the material quite interesting for spintronic applications.The electrical resistivity in a zero field was measured on both cooling and warming modes,and the data obtained were fitted by using different theoretical models.At low temperatures,the resistivity shows the presence of insulator-metal transition and is found to be in conformity with the magnetization data.A magnetic training effect due to the thermo-magnetic history dependent behavior is observed,where the resistivity is consistently irreversible.     

Numerical Simulation and Applications of F-EMS for High Carbon Steel Billet

The distribution of electromagnetic fields and electromagnetic force of F-EMS were simulated by ANSYS12.0 software. The magnetic induction intensity and electromagnetic force of billet with various stirring parameters were cal- culated, then the relationship between the magnetic induction intensity and electromagnetic force was calculated. The results showed that the electromagnetic force is not positive with the magnetic induction intensity. Depending on the com- bination of the practical production, the central segregation of high carbon steel SWRH77B is improved effectively under the best stirring parameter that the current is 360A and the frequency is 12Hz.     

Large Magnetostriction of Fe-Ga Alloys by Solidification With a Static Magnetic Field

A simple but effective process to fabricate the bulk and practical Fe-Ga alloys at low fields is proposed just by applying a static magnetic field to their solidification process.We have introduced a static 1-T magnetic field to solidify the Fe-17%Ga alloys.The results indicate that the magnetostriction of a polycrystalline textured Fe-17%Ga alloy is increased about threefold by solidifying with a 1-T magnetic field compared to that without a magnetic field.This large magnetostiction could be attributed to the increasing volume fraction and the strong texture of the disordered a-Fe phases.The systematic analysis shows that they are originated from the undercooling and orientation effects induced by the imposed magnetic field during the solidification process.     

Morphology Change of Electrodeposited Calcium Phosphate Coating on Ti6Al4V Substrate Under High Magnetic Field

The present study reports on the growth of calcium phosphate coatings on Ti6A14V substrate by electrodeposition under high magnetic field.The electrodeposition is conducted by potentiostatic method on horizontal electrode whose roughness was modified to reach a value of 3μm.The coatings are obtained from an electrolyte containing calcium nitrate as the Ca²⁺source and ammonium phosphate as the P source with a Ca/P ratio equal to two.The LNCMI high field continuous magnet in a 170 mm bore with homogeneity of 600.10^-6in 1 cm³ has been used.The magnetic field with a magnitude up to 12 T is applied perpendicularly to the electrode surface.The surface morphology and chemical composition of the obtained coatings were characterized by 3D digital microscope and scanning electron microscopy associated with X-ray microanalysis（SEM-EDX）.The phase composition was analyzed by X-Ray diffraction.The presence of several crystalline phases comprising octacalcium phosphate and hydroxyapatite is obtained and magnetic field seems to change the relative importance of these phases.The coating morphology changes from belt shape crystallites to needle shape crystallites with high magnetic field superimposition without important modification of Ca/P ratio in the deposit.On the other hand formation of volcano-like structures due to the presence of hydrogen bubbles during deposition is considerably reduced in the presence of magnetic field.     

Influence of zirconium addition on microstructure, magnetic properties and thermal stability of nanocrystalline Nd12.3Fe81.7B6.0 alloy

Effect of Zr addition on microstructure, magnetic properties and thermal stability of Nd12.3Fe81.7B6.0 (x=0-3.0) ribbons melt-spun and annealed was investigated. Magnetic measurement using vibrating sample magnetometer (VSM) revealed that Zr addition was significantly effective in improving the magnetic properties at room temperature. The intrinsic coercivity Hci of the optimally processed rib-boris increased monotonically with increasing Zr content, from 751.7 kA/m for x=0 to 1005.3 kA/m for x=3.0. Unlike the coercivity, the re-manence polarization Jr increased first with Zr addition, from 0.898 T up to 1.041 T at x=1.5, and then decreased with further Zr addition.The maximum energy product (BH)max behaved similarly, increasing from 103.1 KJ/m3 to a maximum of 175.2 kJ/m3 at x=1.5. Microstruc-ture studies using atomic force microscopy (AFM) and transmission electron microscopy (TEM) had shown a significant microstructttre re-finement with Zr addition. The absolute values of temperature coefficients of induction and coercivity were significantly increased with in-creasing Zr content, indicating that Zr was detrimental to thermal stability of the melt-spun Nd2Fe14B-type material.     

The Impact of an Oxidised Surface on the Melt Flow Driven by a Rotating Magnetic Field in a Cylindrical Column

This paper considers the situation where the liquid metal flow with a free surface covered by an oxide layer is driven by a rotating magnetic field.The cylindrical configuration was investigated in an experiment accompanied by numerical simulations.The oxide layer feels the effect of the viscous force arising from the moving liquid beneath and the friction force from the side walls.A complex interaction occurs if both forces are in the same order of magnitude.Our measurements demonstrate that the occurrence of the oxide layer may lead to an unexpected oscillating behaviour of the bulk flow.Our numerical model was shown to be able to reproduce essential features of the phenomenon in a qualitative way.     

Material Determination of Vehicle Part Using Strain Analysis Method

The experiment regarding material determination of a vehicle part was conducted.The experiment on stamping production of a part using the steels A, B and C was made. The strain data on the deformed parts were measured. The forming limit diagrams for the steels were examined and evaluated. The results show that three steels are unsuitable for this stamping part. The desired material properties with an optimal strain hardening exponent value were determined using experimental and analytical methods. The steel D was chosen as a desired material. The results show that the steel D is appropriate for mass production. In addition, the feasibility of the application of thinner material to this part was studied. The validity of the material selection was verified theoretically and experimentally.     

Synthesis of Magnetically Intensified Aluminosilicate

Intensification of magnetic susceptibility of the zeolite ensures not only quick and reliable separation of the zeolite from waste medium by using a magnetic separation but also efficient micro-wave heating of the zeolite.Thus,reinforcement of magnetic susceptibility of the zeolite has been attempted.In this study,a composite material has been synthesized by adding magnetite during a synthesis process of the zeolite.And the composite was evaluated by using XRD and SEM.It was composed of zeolite and magnetite.And,its shape was polygonal with a few micrometers size under the synthesis time of 4 weeks.Its magnetization in magnitude was about 400 times larger than that of the normally synthesized zeolite.And the mass ratio of the zeolite and the magnetite in the synthesized material was estimated at about 7.8:1.     

Sputtering-pressure dependence of magnetic properties in amorphous Tb_（40）（FeCoV）_（60） films

The Tb40(Fe49Co49V2)60 films were fabricated by magnetron cosputtering from a multiple target arrangement at different argon pressures.The samples were investigated using X-ray diffraction,magnetic force microscope and vibrating sample magnetometer.A strong perpendicular anisotropy was obtained for the sample prepared at 0.4 Pa.The easy direction of magnetization could be turned from perpendicular to in-plane direction either at high working pressures(P Ar >2.0 Pa) or by annealing at temperatures higher than 250 °C.An excellent magnetic softness with coercivity below 3 mT and saturating field of 20 mT in film-plane direction was obtained for the sample prepared at 0.7 Pa and then annealed at 350 °C.     

Magnetic property and microstructure of SmCo magnetic recording films

Cr/SmCo/Cr thin films with Sm concentration of 37.7 at.% were deposited on glass substrates by magnetron sputtering. Meas-urement of magnetic properties showed that the SmCo film possessed good magnetic anisotropy, a high coercivity of 3019 kA/m and low magnetic exchange coupling. Microstructure analysis showed that crystallized SmCo5 magnetic phase, non-magnetic SmCo2 phase and Sm2Co7 phase co-existed ill the film. The non-magnetic SmCo2 phase might function as isolator of SmCo grains, leading to a decrease of magnetic exchange coupling. Moreover, a Cr2)3 oxide layer which could protect the SmCo layer from oxidation formed at the surface of the Cr cap layer.     

Effect of Static Mgnetic Fields on the Recalescence Behavior of Undercooled Co-Sn Liquid

The recalescence behavior of undercooled Co-Sn alloys under static magnetic fields was investigated using glass slag fluxing technique in a 12T superconducting magnet.Results indicated that the nucleation temperature and the highest temperature after recalescence of undercooled melt can be affected by the static magnetic field.The undercooling for Co-Sn alloys keep unchanged when a strong magnetic field was applied while the recalescence extent was reduced.With the increasing Co content for Co-Sn eutectic systems,the effect of the magnetic field on the recalescence was strengthened.We find that the magnetic field has very limited effect on the nucleation temperature on alloys while the highest temperature after recalescence is affected by the field depending on the magnetization difference of the undercooled melt before and after solidification.     

Effects of High Magnetic Field on Microstructure and Properties of Low Aspect Ratio Bi₂Sr₂CaCu₂O_x/AgMg Wire

Here,we report the effect of an 8 T magnetic field on the microstructure and properties of a reetangular Bi₂Sr2CaCu20x/AgMg（Bi2212/AgMg）conductor with low aspect ratio.The magnetic field was applied during split melt process with the field direction perpendicular and parallel to the wide surface of the conductors.After heat treatment,the conductors were electrically characterized using four-point critical current measurements as a function of magnetic field and magnetic field orientation relative to the conductor.The superconducting transition and magnetization hysteresis were measured using a SQUID magnetometer.The microstructure was characterized using scanning electron microscopy.It was found that the presence of magnetic field during split melt processing enhances the electrical transport and magnetic behavior.The magnetic field increases the Bi2212 grains alignment and long range texture within filaments and bridges between filaments by textured growth of Bi2212 phase.     

Modeling of Orientation and Alignment of Primary Al₃Ni Crystal in Al-Ni Alloy by Imposing a High Magnetic Field

Regarding Al₃Ni crystal as a rigid ellipsoid,a model describing the orientation and alignment of a primary paramagnetic Al₃Ni crystal in Al-Ni alloy solidification under a high magnetic field is developed.The model is based on rigid body rotation dynamics model as well as the magnetic dipole model,respectively.It describes the rotational motion of a magnetic anisotropic crystal around its centroid and around one endpoint of its crystal axis.The orientation time and the orientation characteristics with the intensity of magnetic field,the aspect ratio of the crystal and the effective viscosity of the melt,as well as the crystal growth,are deeply discussed for single grain.Furthermore,the interaction between two crystals during the alignment in high magnetic field are analyzed based on the magnetic dipole model,in which the final state of the grain is dependent on the attractive interaction force between two neighboring grains and the magnetization force acting on each grain.The prediction shows fitness with the experimental and theoretical results in literature.     

Research on the grain refinement under pulsed magnetic field

In this paper,the principle of Pulsed Magnetic Field(PMF) force was analyzed through mathematical analyses.By theoretical analysis and calculation,the results show that the great electromagnetic force is made in the melt under pulsed magnetic field,as well as changing its direction in different places of melt at the same time.It enforces the crystallizing nucleus and brittle crystallite to fragment in the solidification processing.From the point of view,one of the main factors of grain refinement is that the fragmentations occur under a pulsed magnetic field by preliminary judgement. The feasibility of application in the metallurgical industry under PMF was discussed through comparing the results of grain refinement under EMS.According to the theoretic calculation,the power consumption under EMS is 5 -8 times the amount under PMF,when both of magnetic flux density B are 0.07T.That is to say,the better effect on grain refining can be obtained under PMF,compared with EMS,even in the lower power consumption.The solidification experiments of Sn-20%Pb alloy are conducted under the same experimental conditions that the magnetic intensity is 0.07T in the center of the crucible,it also shows that PMF has a better effect on grain refining than EMS. Combined with the continuous casting process,the influence of pulsed parameters and the metallurgical effects with applying PMF at different solidification stages was investigated.There are different grain refining effects under PMF in different solidification stages,and there are different grain refining effects under PMF in different PMF parameters.For the Sn-20%Pb alloy or silicon steel,it is more effective during the initial stage,in which the pulse frequency is 5Hz.For the Sn-20%Pb alloy,the average grain size ofβphase is the smallest,when applying the PMF during the temperature of melt decreasing from 201℃to 184℃.Further investigation of the specified technique parameters for industrial applications are required.