Optimizing process windows for minimizing the pore size of Ni-based single crystal superalloys

Minimizing pore size during directional solidification is critical for reducing the risk of failure for Ni-based superalloys. In this study, the pore size distribution as a function of casting conditions during the entire single crystal casting was obtained by two-dimensional optical metallography and three-dimensional X-ray microtomography. Then, the relationship between the pore size and local thermal conditions was implemented as a subroutine in a finite element model. Both simulation and experimental results show that the temperature gradient and withdrawal rate play the most significant roles in the pore size distribution. Besides, the influences of withdrawal rate and temperature gradient on the mushy zone length, lateral-axial thermal gradient ratios were also investigated. Combining the characterization results with simulation models, a computationally effective method was developed to optimize the processing window of directional solidification and further reduce the pore size.