Influence of withdrawal rate on last stage solidification path of a Mo-rich Ni₃Al based single crystal superalloy

The solidification behaviors of a Mo-rich Ni₃Al based single crystal superalloy at different withdrawal rates were investigated. Experimental analysis and thermodynamic calculation (by JMatPro) both indicated that the high Al and Mo contents in residual liquid promoted the precipitations of γ′ and Mo-rich phases at the last stage of solidification. Mo-rich phase in the cellular microstructure was only α-Mo phase, while two types of Mo-rich phase - α-Mo and γ/NiMo eutectic phases existed in the dendritic microstructures. Solid back diffusion during solidification led to the volume fraction of interdendritic precipitation initially increasing and then decreasing with increasing withdrawal rate.