Evolution behavior of competing fatigue failure and life prediction related to defect, stress and temperature for laser powder bed fused superalloy with solution aging treatment

Laser powder bed fusion (LPBF) provides advanced manufacturing capabilities for nickel-based superalloy, and solution aging treatment enhances its mechanical properties. However, the fatigue properties of solution-aged LPBF nickel-based superalloy at elevated temperature are not fully well understood. Here, high-cycle and very-high-cycle fatigue tests are conducted at 650 °C with stress ratios of R = −1 and 0.1. Microstructures and fatigue fractures are analyzed using various techniques, including scanning electron microscopy, X-ray computed tomography, electron backscatter diffraction, and three-dimensional ultra-depth of field imaging. The results indicate that solution aging blurs the laser tracks and melt pool prevalent in the LPBF process. The synergistic interaction of δ, γ′, and γ″ phases improves fatigue properties. Four defect-induced internal failure modes caused by facet, pore, lack of fusion, and inclusion are revealed. Internal microcracks grow in a trans-granular fracture mode under shear forces. The aggregation of facets formed during crack growth is a typical feature of internal failure. Interestingly, even for internal failures, the crack nucleation site gradually shifts from the subsurface to the center as the stress level decreases, accompanied by an increase in the facetted cracking area. A fatigue life prediction model related to the effects of defect features, stress, and temperature is established.