Stress-medium synergistic hot corrosion failure mechanism and kinetics model of a Ni-based superalloy

The hot corrosion behavior of a Ni-based superalloy was investigated under tensile stresses of 0, 60, and 120 MPa at 750 °C using XRD, OM, SEM, and EDS. The corrosion medium consisted of a 75 % Na₂SO₄–25 % NaCl salt mixture. The influence of tensile stress on oxide film microstructure, elemental diffusion, and corrosion kinetics was systematically analyzed. Results revealed that tensile stress accelerated hot corrosion via two key mechanisms: (1) enhancing the bidirectional diffusion of Cr and S, and (2) degrading the oxide film's integrity. The thickness of Cr-depleted layers, which varied with applied stress, served as a quantitative indicator of corrosion kinetics. The corrosion process progressed through three distinct stages, corresponding to oxide film growth, cracking/spalling, and reformation. A synergistic degradation mechanism was proposed, combining stress and hot corrosion effects. Outward Cr diffusion initially formed a protective Cr₂O₃-rich layer, but tensile stress and corrosive salts jointly shortened its protective lifespan. Subsequent Cr₂O₃ spalling enabled deeper salt penetration, inducing grain boundary embrittlement and accelerated substrate degradation.