Magnetostriction Increase of Tb0.3Dy0.7Fe1.95 Alloy Prepared by Solidification in High Magnetic Fields

Tb0.3Dy0.TFe1.95 alloys are solidified under various high magnetic field conditions. The influence of a high magnetic field on the crystal orientation, morphology and magnetostriction of the alloys are studied. The results show that with the increase of magnetic flux density, the crystal orientation of the （Tb,Dy）Fe2 phase changed from （113） to （111） direction; the grains in the alloys tended to align along the magnetic field direction; and the magnetostriction of Tb0.3Dy0.7Fe1.95 alloys is remarkably improved. The change in magnetostriction of Tb0.3Dy0.TFe1.95 alloys is linked to the amount and the crystal orientation behavior of the （Tb,Dy）Fe2 phase.

Effect of high magnetic field on solidification microstructure evolution of a Cu-Fe immiscible alloy

The liquid phase separation behavior and the evolution of the solidification microstructure of a binary Cu_(50)Fe_(50) alloy were investigated under the conditions of without and with a 10 T magnetic field,with different undercooling during the solidification process.Results show that the combined effect of Stokes motion and Marangoni convection leads to the formation of the core-shell structure under the condition without the magnetic field.In addition,specific gravity segregation is reinforced by increasing the undercooling,resulting in Fe-rich phase drifts towards the sample edge.In the 10 T magnetic field,the Fe-rich phase is elongated in the parallel direction of the magnetic field under the action of demagnetization energy due to the difference of static magnetic energy and surface energy.In the vertical direction,through the action of Lorentz force,the convection in the melt is inhibited and Fe-rich phase becomes more dispersed.Meanwhile,the diffusion of the two phases and the coagulation of the Fe-rich phases are also restrained under the magnetic field,therefore,the phase volume fraction of the Fe-rich phase decreases at the same undercooling in the 10 T magnetic field.The magnetic field inhibits the segregation behavior in the vertical direction of the magnetic field,and at the same time,improves the gravitational segregation to a certain extent,which has a very important impact on microstructure regulation.

Solidification structure of eutectic Al-Si alloy under a high magnetic field-aid-electromagnetic vibration

An electromagnetic vibration was generated by simultaneously imposing a strong static magnetic field （up to 10 T） and an alternative electricity current to the metal. Its effects on the solidification structure of eutectic Al-Si alloy have been investigated experimentally. It is found that the eutectic structure has been refined by solely imposing high magnetic field while it is coarsened under the electromagnetic vibration. Furthermore, polyhedral Si grains and non-dendritic α-Al appeared when the electromagnetic vibration strength was strong enough. The refining of eutectic structure is attributed to the decrease of diffusion coefficient caused by the strong magnetic field. The coarseness of eutectic structure may be attributed to the convection caused by electromagnetic vibration. Strong convection may break co-operative growth of eutectic phases to form polyhedral Si grains and non-dendritic α-Al.

Solidification structures of Bi-Mn alloys under a high magnetic field

Solidification structures of Bi-Mn alloys solidified in a magnetic field up to 10 T were investigated experiemtaliy. The solidification of the alloy from melt or semisolid in the magnetic field was carded out. The alignment-retaining behavior of the alignment of BiMn structure during reheating of the alloy, which was obtained by solidification in the magnetic field, was also investigated. It was found that with different temperatures of starting solidification the structures were varied, namely, in the temperature zone below Curie point a rod-like BiMn gains appeared, in the zone above Curie point and below the liquidus a flake-like BiMn grains appeared, and in the case of completed melt tightly piled flake-like BiMn grains were produced. In all these cases, the grains were aligned and orientated with 〈 001 〉 along the direction of the field. When the alloy with rod-BiMn grains was reheated to below Curie point, the alignment of the BiMn was kept, while reheated to above Curie point, the alignment was destroyed.

Alignment of primary Al_3Ni phases in hypereutectic Al-Ni alloys with various compositions under high magnetic fields

Al-Ni hypereutectic alloys with various compositions were solidified under various magnetic field con- ditions to investigate the alignment of primary Al3Ni phases. The results showed that the application of high magnetic fields could improve the homogeneity of the primary Al3Ni phase distribution and induce the alignment of primary Al3Ni phases in the direction perpendicular to the magnetic field direction to form chain-like structures. However, the alignment was different from the orientation of the Al3Ni phases. Furthermore, the degree of the alignment decreased with the increasing concentration of Ni element. This can be attributed to the combination effects of high magnetic field and alloy composition on the concentration field around the crystallized primary Al3Ni crystals.

Al-7Si Alloy Directional Solidification With the Application of a Pulsed Magnetic Field

An experiment on the directional solidification of A1-7Si alloys under the influence of a pulsed magnetic field(PMF)is performed.Maximal peak value of PMF intensity up to 0.226 T between two iron cores was generated when a capacitor bank of 120 μF capacitance with initial voltage of 1000 V was triggered to a pair of solenoids.The PMF decreases the temperature gradient ahead of the liquidus front and increases the width of the mushy zone.In this paper, using Darcy's permeability law and Lehrnann's model,the order of magnitude of the interdendritic liquid flow velocities with the application of PMF is evaluated.

Influence of high magnetic field on as-cast structure of Cu-25wt.%Ag alloys

To investigate the influence of high magnetic field (HMF) on the solidification microstructure of Cu-25wt.%Ag alloy, the Cu-25wt.%Ag alloy was prepared under HMF of 12 T, and for comparison, the alloy solidified without HMF was also fabricated. Macro and microstructures of the alloys were observed using the stereomicroscope, and scanning electron microscope, field emission scanning electron microscopy. The weight percentages of the pro-eutectic and eutectic, Cu phase and Ag phase in eutectic, and precipitates of Ag phase in pro-eutectic were analyzed by using of IPP software. Results show that the morphology of the column dendrites changes into cellular dendrites and the grains are refined under HMF of 12 T. Meanwhile, the thickness of the eutectic wall increases, but the sizes of Cu phase and Ag phase and the eutectic lamellar spacings are decreased. The Ag precipitates in the Cu matrix become coarser and sparser. The weight percentage variation of the phases in the microstructure and the Cu-Ag binary phase diagram reveals that the eutectic point moves to the left of the eutectic point in the equilibrium condition and the supersaturated solid solubility of Ag decreases under HMF.

Phase field modeling of dendrite growth

Single dendrite and multi-dendrite growth for Al-2 mol pct Si alloy during isothermal solidification are simulated by phase field method. In the case of single equiaxed dendrite growth, the secondary and the necking phenomenon can be observed. For multi-dendrite growth, there exists the competitive growth among the dendrites during solidification. As solidification proceeds, growing and coarsening of the primary arms occurs, together with the branching and coarsening of the secondary arms. When the diffusion fields of dendrite tips come into contact with those of the branches growing from the neighboring dendrites, the dendrites stop growing and being to ripen and thicken.

Three dimensional dendritic morphology and orientation transition induced by high static magnetic field in directionally solidified Al-10wt.%Zn alloy

Effect of high static magnetic field on the dendritic morphology and growth direction in directionally solidified Al-10 wt.%Zn alloy were studied by three-dimensional(3D) X-ray micro-computed tomography, Electron Back-scattered Diffraction(EBSD) and X-ray Diffraction(XRD). The application of high static axial magnetic field(5T) during directional solidification was found to destabilize the solid/liquid interface and cause the growth direction of dendrite deviate from thermal gradient, leading to irregular solid/liquid interfacial shape and cellular to dendritic morphology transition. The thermoelectric magnetic convection(TEMC) caused by the interaction of thermoelectric effect and magnetic field was supposed to be responsible for the transition. In addition, the EBSD and XRD results confirm that the preferred growth direction of α-Al was found to transform from the traditionally expected <100> to<110>. The dendrite orientation transition(DOT) in Al-10 wt.%Zn alloy can be attributed to the effect of applied magnetic field on the anisotropy of crystal during solidification. The result indicates the potential application of high static magnetic field in altering the morphology and preferred growth direction of dendrite during directional solidification.

Effect of a High Magnetic Field on the Microstructure During Directionally Solidified Sn-20wt.%Pb Hypoeutectic Alloy

The microstructures of Sn-20wt.%Pb hypoeutectic alloy directionally solidified under a longitudinal magnetic field were investigated.The results show that the application of a high magnetic field has a great influence on the morphology of primary β-Sn phase at a temperature gradient of G_L=52 K/cm.At a certain growth speed,with the increase of magnetic field intensity,the magnetic field causes the primary β-Sn phase irregular and to be deformed,further,the magnetic field promotes the columnar to equaixed transition(CET).Further,the thermoelectric magnetic force(TEMF) imposed on the dendrite under a high magnetic field has been calculated and the results show that the numerical magnitude of the TEMF during directional solidification under a 10 T high magnetic field is about 10~4N/m^3 and this force should be responsible for the occurrence of the CET in the Sn-Pb alloy.This may act as an experimental proof that the coupling of temperature gradient and high magnetic field will induce the occurrence of the CET in Sn-Pb alloy.Above phenomena may be attributed to the thermoelectric magnetic force(TEMF)in solid.

Effect of High Magnetic Field on Solidified Structure and Properties of Cu-Cr In Situ Composite

The microstructure of ripening processed Cu-15%Cr alloys and deformed samples were examined under a 12T high magnetic field.The high magnetic field has accelerated the Ostwald Ripening process of Cr phase,the Cr-rich particles in 12T HMF case are coarser compared with 0T case.The 12T high magnetic field increased the peak strength of Cu(111)crystal plane and Cr(110)crystal plane,and appeared to has an orientation effect.Compared with the 0T case, the 12T high magnetic field case decreased the tensile strength and hardness.

强磁场下Cu-50%Ag合金定向凝固过程中的组织及固液界面形貌演变

目的研究强磁场下Cu-50%(质量分数)Ag合金定向凝固过程中的组织演变、固液界面形貌变化及溶质迁移行为,分析强磁场对金属凝固过程的作用机制,为强磁场下的金属材料制备提供理论借鉴和指导。方法在不同的凝固速率与磁场条件下进行定向凝固和淬火实验,对合金的定向凝固组织、糊状区与固液界面形貌以及溶质分布行为进行考察。结果强磁场破坏了凝固组织的定向生长,使凝固组织转变为枝晶与等轴晶共存的形貌;强磁场诱发了熔体对流,减少了糊状区中溶质的含量;强磁场改变了固液界面处的溶质分布和固液界面形貌,破坏了固液界面的稳定性。结论强磁场通过洛伦兹力和热电磁力的共同作用,诱发了糊状区内液相的纵向环流,改变了固液界面及糊状区中的组织形貌与元素分布。

强磁场对Cu-80%Pb过偏晶合金凝固组织的影响

通过比较4种实验条件下Cu-80%Pb(质量分数)过偏晶合金的凝固组织,研究了冷速、磁场对过偏晶合金组织中富Cu相的形态和形成机制的影响.实验结果表明,球形富Cu相主要有3种形态,即"网壳型"、"卵型"、"眼型".冷速对Cu-80%Pb宏观和微观组织有较大的影响.随着冷速的降低,Pb基体中的富Cu相由细小的球形转变为上浮聚集的粗大球形,直至全部上浮至试样顶部,富Pb基体中只保留Cu枝晶.冷速的降低使得富Cu球壳的厚度增加,其内部的网状组织粗化;施加12T强磁场能够抑制富Cu液滴的上浮和富Pb相的沉积,对Cu-Pb合金的重力偏析产生一定的抑制作用,所得到的偏晶合金宏观和微观组织与无磁场时冷速较快的组织类似.对于较大的富Cu液滴,强磁场具有抑制Cu溶质迁移的怍用,抑制了球壳的增厚和网状组织的粗化.对有无磁场作用下富Cu液滴受到的作用力和运动终端速度进行了分析和计算。

强磁场下过共晶铝硅合金凝固过程中初晶硅的迁移行为

研究了在磁场梯度约为25T/m条件下不同磁场强度以及磁场强度约为5T时不同磁场梯度对半熔态Al-18Si合金凝固过程中初晶硅迁移行为的影响。结果表明:当磁场强度大于2.3T时,初晶硅开始迁移,但没有偏聚;当磁场强度达到6.6T时,初晶硅发生迁移并聚集,产生明显的聚集层;且随着磁场强度的进一步增大(磁场强度分别增至7.7和9.9T),聚集层的厚度基本保持不变;当磁场强度不变,随着磁场梯度的增大,初晶硅的偏聚量增加,晶粒尺寸变小。并对磁场强度影响初晶硅迁移的机制进行了探讨。

旋转磁场作用下的Pb-Sn合金组织研究

研究了旋转磁场对Pb-48%Sn亚共晶合金和Pb-67%Sn过共晶合金凝固组织影响的作用机理,对比分析在常规条件下和旋转磁场条件下Pb-48%Sn-0.1%Ce、Pb-80%Sn-0.1%Ce的合金凝固组织的形貌特征。实验证明:旋转磁场能够引起Pb-Sn合金熔体内部的流动,达到改善Pb-Sn合金比重偏析、细化晶粒和提高该合金综合性能的效果。此外,对于Pb-48%Sn、Pb-67%Sn合金,研究发现450mT静磁场的作用效果不明显。

纵向强磁场对定向凝固Al-4．5％Cu合金显微组织的影响

强磁场可明显影响Al-4．5％Cu(质量分数)合金定向凝固组织,在温度梯度G_T=38 K／cm,生长速率较低(R=5μm／s)时,10 T强磁场使液-固界面处的树枝晶变得不规则,低于共晶温度以下的固相区定向枝晶组织消失,组织细化；在生长速率R=50 μm／s时,10 T强磁场使得枝晶沿与凝固方向成一定角度定向排列,X射线衍射表明(111)方向转向磁场方向；在生长速率较高(R=100 μm／s)的情况下,10 T强磁场使得枝晶粗化,一次枝晶间距增大,从热电磁流体理论和磁晶的各向异性角度分析了上述现象。

纵向强磁场对Al-0.85%Cu合金定向凝固界面稳定性和形态的影响

研究纵向稳恒强磁场在定向凝固Al-0.85%Cu(质量分数)合金平面晶-胞晶转变过程中,对界面失稳程度及胞晶形貌的影响。结果表明:随着磁场强度的增加,界面失稳程度先变小后变大,最后又变小;磁场强度为1 T时,界面失稳程度最大,胞晶间距先减小后增大;磁场强度为4 T时,胞晶间距达到最小值;同时,磁场也使得胞晶形貌变得不规则。采用磁阻尼效应和热电磁对流(TEMC)相互竞争的机制来解释相关现象。

强磁场下Bi-Mn合金中形成的MnBi相凝固组织

对强磁场作用下Bi-Mn合金分别从全熔态和从固液两相区开始的凝固过程及其组织的实验研究表明,磁场使初生MnBi相在试样外侧呈环状偏聚,其自身生长为棒状,棒的长轴沿磁场方向呈定向规则排列,而试样心部基本无初生MnBi相在Curie点以上开始进行较慢的凝固时,由片状聚合而成的棒状MnBi具有单晶特征,对以上现象的形成原因进行了分析。

强磁场作用下偏晶合金取向凝固组织的形成

研究了强磁场对Fe-49Sn和Cu-40Pb偏晶合金凝固组织的取向作用。研究结果表明,在强磁场作用下,Fe-49Sn和Cu-40Pb偏晶合金都形成具有一定取向的凝固组织。施加10T强磁场后,α-Fe晶体的磁各向异性和α-Fe枝晶的择优取向促使了Fe-49Sn偏晶合金形成沿平行磁场方向取向排列的富Fe相枝晶凝固组织,α-Fe的(110)晶面衍射强度明显增强;在12T强磁场作用下,强磁场对富Pb相小液滴运动及凝固前沿熔体流动的抑制作用,促使Cu-40Pb偏晶合金试样中心形成较长的规则排列的富Pb相棒状组织。

强磁场对Cu-40%Pb偏晶合金凝固组织的影响

在强磁场作用下进行了Cu-40%Pb偏晶合金的凝固实验,研究了偏晶共生组织的凝固形态.实验结果表明:12 T强磁场的作用使富Pb组织形态发生变化,试样中部及下部的棒状相伸长,在试样中部形成了超长规则排列的棒状富Pb相.凝固前沿富Pb小液滴的运动及分布是决定共生组织中棒状相形态的决定性因素.施加强磁场可改变富Pb基体的表观黏度,从而对凝固前沿的富Pb小液滴运动及附近流体流动产生抑制作用,这被认为是规则排列的超长棒状相的形成原因.