Microstructure and Mechanical Properties of Ni-based Superalloy K418 Produced by the Continuous Unidirectional Solidification Process

Adopting effective strategies to control the solidification structure of Ni-based superalloys is a very interesting subject for metallurgists. Despite the achievement of developing and applying the continuous unidirectional solidification process in simple alloys, the utilization of this process for K418 alloys has been ignored. The microstructure and mechanical properties of a K418 alloy ingot produced by the continuous unidirectional solidification process were investigated. We found that the γ dendrites were typically cross-shaped in the transverse section. The orientation of surviving grains along the casting direction was <001> during competitive growth. The secondary dendrite arm spacing was 32.3 ± 2.5 μm at a cooling rate of 1.75 ± 0.35 °C/s from the surface to the center of the K418 alloy ingot. Due to the higher cooling rate than that of the conventional casting process, a more uniform microstructure and finer γ′ precipitation were obtained in the ingot. Thus, compared with the conventional casting, the tensile strength and the elongation are increased by 8.4 and 21.3%, respectively, at 25 °C. The tensile strength and elongation increased by 15.2 and 49.3%, respectively, at 800 °C. In addition, the fracture surfaces exhibited numerous typical dimples and dendritic fracture characteristics.