为了进一步细化镍基单晶高温合金的微观组织与提升元素分布均质化程度，本工作研究了纵向静磁场对镍基单晶高温合金DD98M定向凝固组织与微观偏析的影响与作用机制，基于Kurz-Fisher模型获得了非平衡固相线与枝晶尖端之间的温差(ΔT')与温度梯度(G)的比值与磁场强度的对应关系，以及枝晶尺度内凝固各阶段的有效分配系数和枝晶干与枝晶间的平均有效分配系数。结果表明，随着磁场强度的增大，DD98M合金的一次枝晶间距减小，γ/γ'共晶组织细化，γ'相尺寸减小，且枝晶间的γ'相逐渐规则化；磁场能有效抑制微观偏析，随着磁场的增大，Al、Ta、Co、W等元素的偏析程度逐渐降低。静磁场下合金的微观组织细化归因于磁场在熔体中引发的热电磁对流导致ΔT' / G的降低或过冷度的增加，而枝晶尺度上合金元素偏析降低本质上是磁场使元素的有效分配系数更趋近于1。

Nickel-based superalloys have been widely used in gas turbines, aerospace, and other fields owing to their excellent high-temperature strength and creep resistance. Advanced directional-solidification techniques allow crystals to grow along specific directions, which can eliminate most or all of the transverse grain boundaries to obtain columnar- or single-crystal superalloys, which further improve the high-temperature mechanical properties. A strong magnetic field can modify the mass-transfer behavior during solidification via magnetic-damping or thermoelectromagnetic effect without contacting the material, thus improving the microstructure and microscopic segregation. In order to further refine the microstructure of nickel-based single crystal superalloys and improve the degree of homogenization of element distribution, the influence of longitudinal static magnetic field with a magnetic field intensity (B) that ranges from 0 to 4 T on the microstructure and microsegregation of liquid-metal-cooling directionally solidified nickel-based single-crystal superalloy DD98M was investigated. OM and SEM were applied to characterize the microstructure. Microsegregation was evaluated using a microsegregation coefficient and isoconcentration contour maps based on different data collection modes embedded in EDS. The results showed that with an increase in B, the primary dendrite spacing, average size of γ/γ' eutectic organization, and size of the γ' phases decreased. Meanwhile, the γ' phase in the interdendrite became more regularized. The microstructure refinement under static magnetic fields was attributed to the decrease in ΔT' / G (ratio of the temperature difference between the nonequilibrium solid-phase line and dendrite tip to the temperature gradient based on the Kurz-Fisher model) or the increase in subcooling of the melt surrounding the dendrites due to thermoelectric-magnetic convection. The relationship between ΔT' / G and B was revealed. The reduction in the γ' phase size was caused by the increase in the nucleation rate of the γ' phase due to the introduction of magnetic free energy difference (ΔG_M) under a magnetic field. The magnetic field depressed the microsegregation of solutes, i.e., as B increased, the segregations of Al, Ta, Co, and W decreased. The effective partition coefficient (k_e) of the dendritic scale and the average effective partition coefficients of the dendritic and interdendritic areas were obtained. It was found that the decrease in macrosegregation was essentially due to the effective distribution coefficient that approached 1 that due to the magnetic field.