Multiple defect-driven high temperature fatigue internal cracking mechanisms of nickel-based superalloy fabricated by laser powder bed fusion at same stress level

Defects generated during additive manufacturing (AM) significantly impact on the fatigue properties of AM materials, but the associated failure mechanisms with some factors including temperature, cycles, and stress are not fully understood. Here, combined with the testing technologies including scanning electron microscopy, three-dimensional ultra-depth of field, and electron backscatter diffraction, the fatigue tests at 650 degrees C with a stress ratio of -1 are performed to investigate the defect-driven failure mechanism for nickel-based superalloy fabricated by laser powder bed fusion (L-PBF). Three different internal failure modes at the same stress level are observed. Results show that the number of crystallography facets increases with the number of load cycles. Fatigue sensitivity levels increase successively in terms of the type, number, size, and location of the defect. The crack growth path is tortuous and exhibits through-crystal fracture. Finally, three internal failure mechanisms of L-PBF nickel-based superalloy are elucidated.