电磁场对镍基单晶高温合金组织的影响

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.