<p>The development of the γ′ (Ni₃(Al,Ti)) and γ″(Ni₃Nb) phases gives excellent characteristics to the niobium-strengthened superalloy Inconel 718. The thermodynamic stability and phase fractions of the high-temperature products, i.e., γ′, γ″, and topologically close-packed (TCP) phases, within the temperature range of 500 °C to 1300 °C for Inconel 718 and its related alloys, were investigated in this study using CALPHAD methodology. Moreover, to investigate the high-temperature effect of Nb in superalloy, the Inconel 718 samples were periodically subjected to salt spray test at temperatures of 35˚C, 650˚C and 750˚C as to relate the weight change due to oxide spallation and corrosion resistance. The EDS analysis confirms the presence of Cr and Nb, so as the formation of protective oxides such as Cr₂O₃ and Nb₂O₅. Consequently, the Nb₂O₅ and Na₂CrO₄ usually form at 650°C at all oxygen partial pressure but at low NaCl pressures. However, NaCl associated with the existence of NbCl₅ and other chlorine-based Nb-products. The Nb based complex oxides and Chlorine-based compounds are created at 750°C. The X Ray Diffraction also confirms the presence of numerous niobium-rich oxides, including NbO₂, Nb₂O₅, and FeNbO₄, in addition to the intermetallic complex Ni₃Nb. The findings support a robust relationship between experimental observations and thermodynamic expectations.</p>