Fatigue crack initiation and propagation behavior of Inconel Alloy 690TT steam generator tube

Fatigue crack initiation and propagation behavior of Inconel Alloy 690TT steam generator (SG) tube under 0.2% strain amplitude were studied by scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD) detector and extended finite element method (XFEM). The results showed that the main crack initiated at the discontinuous interface between the persistent slip bands (PSBs) and the matrix in the grain at the edge of the intrados surface. The metastable crack firstly transgranularly transited to the lateral surface, then penetrated steadily along the direction of maximum shear stress, and finally rapidly propagated perpendicularly to the loading axis, which was consistent with the numerical simulation results. Different fracture modes of specimen shape led to different fatigue lives. The fatigue life of tubular specimen was lower than that of bar specimen, the fatigue life of boat-shaped Alloy 690TT SG tube at 0.2% strain amplitude was 11,476 cycles.