Variation of Homogenization Pores during Homogenization for Nickel-Based Single-Crystal Superalloys

The porosity deteriorates the mechanical properties of nickel-based superalloys, especially the fatigue properties. Herein, the kinetics model of homogenization porosity growth is optimized. The corresponding diffusion processes during solution heat treatment are simulated by the DICTRA software and verified by experiments. The results show that the homogenization porosity increases first and then decreases during the solution heat treatment, due to the imbalanced diffusion flux between dendritic core (DC) and interdendritic areas (IAs). The diffusion flux first flows toward DC and then toward IAs after fully homogenization of the fast diffusion elements. Moreover, the influence of directional solidification parameters on the homogenization porosity process is investigated. With the increase in the withdraw rate, the dendritic structure is refined, and the S-porosity decreases. Meanwhile, the dendritic arm spacing decreases; thus, homogenization accelerated increases. In this case, after the solution heat treatment, the homogenization porosity decreases. The results provide two bases to propose a new method to control the homogenization porosity.