The exceptional stability of Inconel 718 in extreme corrosive environments results from the synergy between its chemical composition design and microstructural features. This article systematically analyzes the chromium-molybdenum cooperative oxidation resistance mechanism, the suppression of pitting nucleation, and the high-temperature oxide film growth kinetics.

1. Chromium-Molybdenum Cooperative Oxidation Resistance System
Chromium content (17–21%) and molybdenum (2.8–3.3%) form a dual protective barrier:

• Chromium creates a dense Cr₂O₃ film, suppressing oxygen diffusion to 1.2×10⁻¹⁴ m²/s (at 900°C).

• Molybdenum forms a MoO₃·Cr₂O₃ composite layer, increasing the bonding strength of the film by 30%.

• In chloride-containing environments, this system reduces the corrosion current density to 0.1 μA/cm² (according to ASTM G59 standard).

2. Pitting Nucleation Suppression Mechanism
The synergistic effect of titanium (0.65–1.15%) and aluminum (0.2–0.8%):

• TiN nanoparticles (30–50 nm) act as defect traps for the passive film.

• Aluminum promotes the densification of the Cr₂O₃ film, raising the pitting potential to +1.2 V (vs SCE).

• In a 3.5% NaCl solution, the critical breakdown potential reaches 1.05 V, superior to 316L stainless steel (0.35 V).

3. High-Temperature Oxidation Kinetics Model
Fitting the Arrhenius equation, the oxidation rate constant at 900°C is 3.2×10⁻¹⁶ g²/(cm⁴·s), which is significantly lower than that of Inconel 625 (1.8×10⁻¹⁵). The oxide film growth follows a parabolic law, with a thickness of only 1.8 μm after 1,000 hours of exposure and no formation of internal oxidation layers.

4. Marine Engineering Failure Case
A certain deep-sea platform riser, after five years of service in a SO₄²⁻-containing environment, exhibited a wall thinning rate of less than 0.05 mm/year. However, it should be noted that:

• When pH < 3, the passivation effect of molybdenum fails.

• Flow rates above 3 m/s can induce erosion corrosion; it is recommended to apply an Al₂O₃ coating to the surface.