Improving the microstructural stability and tensile properties of Inconel 617 superalloy at high temperature by stabilization of the γ′ phase

Coarsening of the γ′ phases in Inconel 617 superalloy during long-term service can cause degradation of mechanical properties. In this study, we investigated the microstructural modulation of γ′ phases in γ matrix by heat treatments to obtain two different initial microstructures of the alloy, and studied their influence on the microstructural evolution and mechanical properties during subsequent service. The solution + sub-solution heat-treated (SST) alloys had not only better short-term mechanical property, but also excellent long-term thermo-mechanical property stability compared to the standard solution heat-treated (ST) alloys. This was mainly attributed to the large number of M23C6 carbides precipitated in the microstructure after sub-solution heat treatment. M23C6 carbides was found to solubilize Al and Ti elements and decrease the solubility of Al and Ti elements in matrix around M23C6 carbides, thus significantly inhibiting the coarsening of γ′ phases during long-term aging. The γ′ coarsening rate of ST alloys is approximately 10 times that of SST alloys. Moreover, we investigated the evolution of deformation mechanisms with γ′ phases coarsening during long-term aging. By analyzing the deformation mechanism, the optimal γ′ phases diameter precipitation range was roughly determined, which has important guiding significance for the subsequent upgrading and optimization of Inconel 617 superalloy.