Development of gas turbine blades has been considered by both university and industrial researchers in the last few years. The effect of withdrawal velocity of a single crystal Nickel-based superalloy on microstructural and mechanical properties was investigated in the current work. For this purpose, directional solidification tests of ceramic mold specimens including spiral grain selector were conducted under determinate withdrawal velocities of 1, 2, 3, 6, and 9 mm/min inside a laboratory-scale Bridgeman vacuum furnace. Microstructural examinations were performed to obtain dendritic spacing. Scanning electron microscopy was used to study the segregation on cross sections of the specimens. Studying the orientation of the single crystal was performed by both EBSD and RO-XRD methods and the results were analyzed. A numerical simulation model for predicting the grain structure of the single crystal was also developed. Microstructure of the specimens include dendrites that are grown opposite but parallel to the heat flux direction. Suddenly increasing the withdrawal velocity results in gradual decreasing of the primary and secondary dendrite spacings. Transition distance of 15, 20, and 25 mm is needed for stability of dendritic structure after 2 to 3, 2 to 6, and 2 to 9 mm/min withdrawal transition, respectively. Results indicated that dendritic structure is dependent upon its initial solidification condition. For a constant secondary velocity, the more the initial velocity, the higher the dendritic spacing will be obtained. Crystal direction measurements obtained from both XRD and EBSD methods represented a good match between two methods. Increasing the initial withdrawal velocity leads to higher misorientation of the single crystal after passing spiral grain selector. Withdrawal transition also induced a misorientation in the single crystal. Results showed that higher initial misorientation results in more severe crystal orientation after withdrawal transition. Examination of hardness of the specimens revealed an increasing trend with increasing withdrawal velocity. High temperature stress rupture tests were also performed on samples. Mechanical tests showed that rupture lives of the samples depend on orientation of the single crystal so that, increasing crystal misorientation leads to decreasing rupture life and strain rate of the specimens. Keywords: Nickel-based superalloy; Single crystal; Bridgeman directional solidification; dendritic microstructure
