High-temperature structure stability and mechanical properties of novel 718 superalloy

Phase transformation from γ″ (bct) to δ (orthorhombic) at 650 °C or elevated temperature is the main obstacle preventing the conventional In 718 alloy from elevated temperature applications. A kind of novel 718 alloy, which offers 30 °C temperature advantage over conventional In 718, was designed and fabricated by adjustment of chemical composition which included the increasing in content of Al + Ti, the ratio of Al/Ti and the level of P and B. Microstructure of the novel 718 alloy at as-heat treated condition was studied. Variety and morphology of the strengthening phase were evaluated by SEM, TEM and SAED observations. High-temperature structure stability and mechanical properties of the novel 718 alloy were examined after long-term exposure at 680 °C. Results indicate that the strengthening phases in novel 718 alloy are spherical morphology γ′-phase and sandwich γ′ + γ″-phases. The unique structure makes this novel 718 alloy have excellent high-temperature structure stability and mechanical properties compared to the conventional In 718.