High temperature structure stability of GH4169 superalloy

The long-term thermal stability of GH4169 superalloy has been studied as a function of heat treatment and thermal exposure. The GH4169 superalloy was subjected to long-term unstressed heat treatment at 650 °C, from 200 to 1000 h. The microstructure, tension and stress rupture properties of the samples before and after long-term thermal exposure were characterized. The coarsening of strengthing phase γ′ and γ″ was observed after exposing at 650 °C. Coarsening of two different precipitates proceeds by Oswald ripening controlled by volume diffusion of solute atoms in the alloy. The tension strength at room-temperature and 650 °C decreases slowly and the stress rapture life decreases remarkably with the increase of thermal exposure time. The decreasing of volume fraction and increasing of mean distance for the precipitates appears to be the main factor in the degradation of the mechanical properties.