Gamma prime particle coarsening behavior at elevated temperatures in cast nickel-based superalloy, GTD-111 EA

Abstract

The objective of this research is to investigate the most appropriate heat treatment condition for a nickel base superalloy GTD-111 turbine blade with the suitable microstructure to enable the phase stability after long-term thermal exposure. The received turbine blade that had been used under load and high temperature showed the coarse gamma prime particles as well as connected to each other and thus forming into larger/longer particles. This result could reduce creep resistance and increases the failure. Therefore, longterm serviced turbine blades were reheated in 6 different conditions for microstructural refurbishment. In this research, 6 reheat treated superalloy GTD - 111 samples were long-term heated under simulated working condition at 1173 K and 1273 K. At every 1800 ks from the beginning of heat treatment until time reached 9000 ks, these samples were collected and the microstructure and size of gamma prime were examined. It was found that with heating at 1173 K, the sample passed the lowest solutioning temperature at 1398 K for 7.2 ks and (secondary) aging at 1118 K for 86.4 ks (with or without primary aging at 1328 K for 3.6 ks), showed the slowest growth of gamma prime size. For heating at 1273 K, all samples after various heat treatments showed similar results in coarsening behavior and quantity of precipitated gamma prime particles.