Dislocation Network and Microstructural Characterization of Directionally Solidified GTD-111 Nickel-Based Superalloy after Long-Term Service Exposure

This study focuses on investigating the effects of long-term service exposure on the microstructure and creep properties of directionally solidified GTD-111 Nickel base superalloy as a land-based gas turbine blade. After a duration of 76,000 h, the examination of the airfoil microstructure through optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM) demonstrated significant changes. These changes included the coarsening of primary γ′ particles, the decomposition of MC carbides, the emergence of needle-like phases, and the formation of dislocation patterns. TEM observations verified that within the critical zone of the airfoil, there was a notable presence of extensive dislocation networks observed in both the γ channels and at the γ/γ′ interfaces. Furthermore, the examination of the creep-tested samples using TEM unveiled the existence of tightly-packed dislocations within the γ channels, accompanied by the occurrence of shearing dislocations in the γ′ phases. Upon analyzing the TEM observations, it has been concluded that the primary mechanism of creep occurring during the service exposure of the examined alloy is a composite process involving the movement of dislocations through gliding, climbing, and cross-slipping.

Graphic Abstract