Microstructures and Nb-Rich Precipitation Behaviors of Inconel 718 Superalloy Under Sub-rapid Solidification Process

The sub-rapid solidification behaviors of Inconel 718 superalloy with a novel droplet solidification technique were investigated by analyzing the heat transfer, macrostructure, microstructure, segregation, and precipitates. It is observed that the Nb-rich precipitates such as Laves phase and (Nb, Ti)C are formed in the interdendritic regions. The results suggest that droplet solidification method is an effective technique to improve the quality of Inconel 718 in terms of enhancing heat transfer, refining grains, reducing secondary dendrite arm spacing (SDAS) and Nb-rich precipitates. In addition, it is interestingly found that the heat flux and columnar grain zone increase, while the SDAS and volume fraction of Nb-rich precipitates decrease as the superheat increasing of 40 K, due to a larger contact area with the mold. Moreover, the quantitative relationship between the SDAS and volume fraction of Nb-rich precipitates is obtained.