Revealing internal corrosion of GH4169 with stress coupled solid NaCl deposited in a humid environment of 600°C

NaCl-deposited specimens of Ni-based superalloy GH4169 have been corroded in a humid environment of 600 °C with elastic stress applied by four-point bending testing. A stress-promoted "active oxidation" mechanism at the internal corrosion zone promotes deeper internal corrosion in an exponential form with external stress. Stress and Cl synergistically change the single corrosion product of Cr 2 O 3 to mixed Cr 2 O 3 and Fe 2 O 3 at internal corrosion tips. Because of increased oxygen vacancy, more oxygen diffuses inward to the internal corrosion zone. Gathered Cl induced by stress participates in the reaction circularly and corrodes metals, leading to the propagation of internal corrosion. • The corrosion mechanism of stress-coupled NaCl at 600 °C was studied. • The internal corrosion depth within the elastic stress range was counted. • The principle of internal corrosion depth versus elastic stress level was proposed. • Mechanism of external elastic stress promoting active oxidation was proposed.