Investigating Macro/Microstructure and Mechanical Properties of the Directionally-Solidified GTD111 Ni-Based Superalloy

In the present work, grain structure, microstructure and mechanical properties of the GTD-111 Ni-based superalloy directionally solidified by the Bridgman method were investigated. Several rod-shaped samples of the superalloy were solidified under different withdrawal rates of 1, 3, 6 and 9 mm/min. The remelting and solidification of the rods were conducted in an investment cast mold installed on a water-cooled copper chill. The cast specimens were then heat treated for mechanical testing. Macro-microstructures of the DS specimens were examined using optical and SEM equipped with EDS. Hardness, room temperature tensile, hot tensile and stress-rupture tests were conducted on the heat treated specimens. The results showed DS grain structure for all the withdrawal rates investigated in which grain competition occurred along the rod axis. Increasing the cooling rate resulted in a decrease in dendrite arm spacing, carbide size, and γ-γ’ eutectic regions, but had no effect on the size of g’ precipitates. The yield and ultimate tensile strengths of the DS specimens were higher than those of the initial conventionally-cast (CC) samples and standard limits, while the tensile elongation was relatively lower than that of the CC one. The stress-rupture properties of the DS specimens were much higher than those of the C ones.