Influence of hot corrosion on thermal fatigue behavior of Ni-based single crystal superalloy: Invisible and accelerated crack.

• Thermal fatigue behavior of Ni-based single crystal superalloy at 25–900 °C are investigated. • The cracks only initiate at the direction of 45° from [0 0 1] direction in hot corrosion environment, which is different from the multi-point initiation of cracks in air environment. • The invisibility of crack morphology in hot corrosion environment deserves to be highlighted. • The influence mechanism of hot corrosion on the thermal fatigue behavior of Ni-based single crystal superalloy is proposed. As an important failure model for single crystal materials in service, with the increasing complexity of working environments, the thermal corrosion fatigue failure needs to be studied urgently. In this study, the thermal corrosion fatigue crack initiation and propagation behaviors of an Ni-based single crystal superalloy in both air and hot corrosion environments at 25–900 °C were studied by using a designed precise thermal fatigue test device. The microstructure characteristics and crack composition were analyzed by SEM, TEM and EDS, and the internal stress and recrystallization during thermal fatigue were characterized by EBSD. Moreover, the detailed and comprehensive crack morphology was characterized with different surface treatments. The results showed that the crack morphology was invisible in the hot corrosion environment, which is worthy of being highlighted. The initiation and propagation of thermal fatigue cracks were also accelerated in the hot corrosion environment, which contributed to the sufficient thermal stress, the accelerated material degradation of the inner/outer layers in the crack region, and the rapid forward diffusion of O 2 in the inner crack layer. Finally, the influence mechanism of hot corrosion on the thermal fatigue behavior of the Ni-based single crystal superalloy is proposed. [ABSTRACT FROM AUTHOR]