Effect of pre-hot salt corrosion on hot salt corrosion fatigue behavior of the TC11 titanium alloy at 500 °C

•The fatigue life decreases greatly with the increase of salt deposition.•The HSCF sensitivity of the TC11 alloy at 500 °C was further increased by PHSC.•Combined effect of cyclic stress and salt broken the protective layer of TiO2.•Local stress concentration of pits accelerated the initiation of fatigue cracks.•Hydrogen and the hydride phase promoted fatigue crack propagation. Pre-hot salt corrosion (PHSC) tests is the samples with 0.1, 0.5, 1 and 4 mg/cm2 salt coating are corroded at 500 °C for 100 h. The hot salt corrosion fatigue (HSCF) tests were conducted on PHSC specimens at a stress ratio, a maximum stress amplitudes and temperature of −1, 450 MPa and 500 °C, respectively. The effect of PHSC on HSCF behavior of TC11 alloy at 500 °C was studied by deposition of solid NaCl. The HSCF sensitivity of the TC11 alloy at 500 °C was further increased by PHSC, and increased gradually with the increase in solid NaCl content. When the salt content exceeded 1 mg/cm2, the HSCF life was reduced by more than 99% compared with the samples without salt coating. The mechanism of HSCF was that the local stress concentration of the corrosion pits accelerated the initiation of fatigue cracks, hydrogen and the hydride phase promoted fatigue crack propagation. The PHSC process promoted the formation of corrosion pits, and accelerated the infiltration of hydrogen into the matrix and hydride formation, so the fatigue resistance of pre hot salt corrosion samples was reduced further. A greater NaCl deposition resulted in more severe surface corrosion damage of the titanium alloy, a stronger coupling of corrosion factors and alternating load in the HSCF process, and a greater reduction in fatigue resistance.