Influence of the thermal exposure on the deformation mechanism of the Inconel 625 superalloy

To evaluate the long-term service safety of the Inconel 625 superalloy in concentrated solar power plants (CSP). This study focuses on the deformation mechanisms of the homogenized and thermally exposed Inconel 625 superalloy. Transmission electron microscopy (TEM) observations reveal that the homogenized sample contains stacking faults (SFs) in its microstructure after room-temperature deformation, and only a small amount of SFs appear during deformation at high temperatures (705 °C). In contrast, the thermally exposed sample exhibits nano-twins after room-temperature deformation and a tiny amount of SF at high temperatures (705 °C). Combined with thermodynamic calculation results, it is indicated that a thermodynamically metastable γ'' phase precipitates in the alloy after thermal exposure. This phase alters the matrix composition, increasing the driving force for SF formation, decreasing the stacking fault energy (SFE), and thereby promoting the generation of SFs (during high-temperature deformation) and deformation twins (during room-temperature deformation). The thermodynamic calculation indicates that the SFE of the thermally exposed alloy is 3.3 mJ/m 2 at room temperature, further confirming the experimental observations. This study not only provides fundamental data for the long-term service of Inconel 625 superalloy in CSP power plants, but also, via the driving force of SF, offers novel insights into alloy deformation mechanisms.