电磁场对镍基单晶高温合金组织的影响

Effect of Electromagnetic Field on Microstructure of Ni-Based Single Crystal Superalloys

利用定向凝固技术,通过改变石墨套厚度获得不同强度的磁场,研究了通电感应线圈产生的磁场对DD90单晶高温合金凝固组织的影响规律,同时结合Ansys有限元分析对合金熔体内磁场、流场分布进行了模拟。结果表明:当石墨套厚度为10～30 mm时,单晶性保持完好;随石墨套厚度的增加一次枝晶间距变大,二次枝晶间距变化规律与之相反,铸态组织析出相g′的尺寸、共晶组织含量明显增加,元素偏析增大。合金熔体内磁场、流场的Ansys有限元模拟表明,随石墨套厚度的增加,熔体内磁场强度、流速均逐渐减弱。在此基础上,从磁场作用下热电磁对流和熔体流动的角度对结果进行了分析和讨论。

With the increase of the alloying degree and structural complexity as well as larger size in Ni-based superalloy blades, it is essentially important to suppress the solidification defects. When the electromagnetic field is introduced into solidification process, the solidification properties of alloy can be modified without changing the alloy composition, which can well eliminate the casting defects, such as the composition segregation, and optimize the solidification microstructure and improve properties. The effect of induction coil magnetic field on solidification structure of DD90 single crystal superalloy is studied by changing the thickness of graphite sleeve. The distribution of magnetic field and flow field in alloy melt are analyzed by Ansys finite element analysis （FEM）. The results show that when the thickness of the graphite sleeve is 10-30 mm, the monocrystalline remains intact and the primary dendrite arm spacing increases with increasing the thickness, while the second dendrites are the opposite rule. Moreover, the as-cast microstructures of γ′ phase size, eutectic structure and content increase significantly, and the element segregation increases simultaneously with increasing the graphite sleeve thickness. The Ansys FEM shows that the magnetic field and flow velocity in the melt decrease with the increase of the thickness of graphite sleeve. Based on the thermoelectric magnetic convection induced by the magnetic field during solidification and the effect of the convection on the microstructure, the above phenomenon is analyzed and discussed.