铸造高温合金的流动性对铸件成形和组织具有重要影响，但目前关于B和Zr元素对合金流动性的影响规律及其作用机制的研究尚不充分。本工作采用螺旋型流动性测试模型、高温激光共聚焦显微镜和双热电偶法等研究了不同B和Zr含量对IN718高温合金的流动性、凝固过程、枝晶搭接点温度及持久性能的影响，探讨了B和Zr复合添加对流动性的影响机理。结果表明，复合添加B和Zr可同时有效提高IN718高温合金的流动性和高温持久性能。合金中B和Zr含量分别为0.0059%和0.042% (质量分数)时，流动性最好，比原始合金提高了90%以上，持久寿命提高了77%。当合金中B和Zr含量较高时，枝晶在糊状区具有较低的生长速率，使得枝晶搭接点温度(T_DCP)降低，增大了液相线温度(T_L)与枝晶搭接温度之差(T_L- T_DCP)，延缓了枝晶搭接，从而有利于提高熔体流动性。

The fluidity of superalloy is an important property in the manufacture of large thin-walled and complex structure castings, but superalloys show high viscosity and a wide solidification temperature range, which may lead to serious defects, low yield, and poor performance. Therefore, the manufacturing of these castings is important to improve the fluidity by regulating the alloy composition. B and Zr, as common elements in superalloys, have important effects on solidification, microstructure, and mechanical properties. However, the effect of B and Zr on the fluidity and mechanism of superalloys remain unclear. In this study, the spiral fluidity test, high-temperature confocal laser scanning microscopy, and double-thermocouple method were used to investigate the fluidity, solidification, dendrite coherency point temperature, and stress rupture property of the IN718 superalloy with various B and Zr contents, whereas the mechanism of the effect of B and Zr on fluidity was also discussed. Results show that the combined addition of B and Zr can improve the fluidity and high-temperature stress rupture property of the IN718 superalloy. At different pouring temperatures, the fluidity of the alloy increases with the increase of B and Zr contents. The optimum fluidity is obtained with 0.0059%B and 0.042%Zr (mass fraction), respectively, which is about 90% higher than that of the original alloy and increases the stress rupture life by 77%. In the IN718 superalloy with a high content of B and Zr, the dendrite growth rate in the mushy zone is low, which reduces the dendrite coherency point temperature (T_DCP), increases the difference between liquidus temperature (T_L) and T_DCP (T_L- T_DCP), delays the dendrite coherency, and improves the melt fluidity.