纵向和横向静磁场作用于单晶高温合金的定向凝固时，热电磁力破坏枝晶界面形态，而磁制动效应显著均匀合金元素在多尺度上的分布，前者恶化力学性能，而后者作用恰好相反，如何克服不利效应而保留有利作用？申请者前期预研证实Cusp结构的磁场规整了枝晶形态并降低其位向偏离度，表明该磁场能解决以上问题，其原因在于该特殊结构磁场对不同部位熔体流动产生不同的作用，进而改变温度和溶质环境，最终影响到枝晶形态和生长行为，申请项目拟对此问题进行深入研究。通过研究枝晶周围热电磁力分布和其对界面附近及远处熔体流动的影响，结合熔体不同部位和方向的温度变化、溶质在宏微观尺度上的分布，探明磁场致使的流动对枝晶生长环境的影响；研究枝晶及宏观液固界面形态、枝晶间距和分布均匀度变化，建立枝晶特征参数、横向温度梯度和成分均匀化之间的关联，最终揭示Cusp磁场增强枝晶形态稳定性和影响生长的机理，为用磁场控制单晶高温合金组织提供理论依据。

When the single-direction longitudinal or transverse magnetic field is applied in the directional solidification of single-crystal superalloy, the thermoelectromagnetic force destroys the stability of the dendrite and liquid-solid interface，and the magneto-hydrodynamic-damping effect homogeneously distributes the alloying elements in the melt. The former effect would deteriorate the mechanical properties, and the latter would benefit the properties. How is the disadvantage effect eliminated and is the advantage role exerted? The applicant has investigated that the effect of Cusp magnetic field on the dendrite morphology and orientation of the single-crystal superalloy. The results show that the dendrite morphology grows more regularly and the dendrite orientation exhibits more less deviation, which indicates that the Cusp magnetic field could eliminate the disadvantage role of the single-direction magnetic field. The effect of Cusp magnetic field on the dendrite structure of single-crystal superalloy is achieved by its influence on the flow field. The change of flow field further produce the effect on the temperature and solute distribute, which finally modify the stability of the dendrite morphology and the growth behavior. Therefore, this proposal will focus on the revelation on the above mechanisms..The profound researches will be conducted on the basis of the following aspects: (1) The distribution of the thermoelectricmagnetic force near the dendrite interface in the Cusp magnetic field would be simulated for clarifying its role in the melt convection. (2) The effect of Cusp magnetic field on the flow field and temperature field during directional solidification will be investigated. This provides the clarification of heat and flow environment, which determines the change of solute field and further modify the stability dendrite and liquid-solid morphology. (3) The solute field will be explored based on the melt convection, the longitudinal macrosegregation, the transverse microsegregation, the effective partition coefficient, the equilibrium partition coefficient, and the composition of mushy zone. This can reveal the solute-field modification that affects the growth behavior of dendrties. (4) The morphology, arm spacing, distribution homogeneity, and orientation of dendrites with Cusp magnetic field in single-crystal superalloys will be studied. Finally, the relationship between the characteristic parameters of dendrite, the transverse gradient of temperature, and the composition distribution along the radial direction would be established during the Cusp magnetic-field-assisted solidification..The research of this proposal will shed light on the effect of Cusp magnetic field on the stability and growth behavior of the dendrties by virtue of the composition homogeneity, the temperature distribution, and the flow field in the different regions during the directional solidification of single-crystal nickel-base superalloy. The regions refers to the mushy zone, the liquid-solid interface, and the far-field fields. The mechanism revelation will provide the theoretical guidance to control the microstructure and properties of single-crystal superalloy. Meanwhile, a potential technology for preparing the high performance of single-crystal superalloy will be developed.