Study on Microstructure and Fatigue Properties of Laser Powder Bed Fusion Nickel-Based Superalloy with Heat Treatment

Laser powder bed fusion (L-PBF) is an advanced metal additive manufacturing process with an excellent capability for fabricating nickel-based superalloys. After solution aging (SA), the L-PBF nickel-based superalloys can match the tensile properties with the conventional manufacturing process; however, its performance under long-life regime service conditions, especially at an elevated temperature of 650 °C, has not yet been well understood, which restricts its promotion in industrial applications. In this study, combined with various techniques including X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and micro-computed tomography (micro-CT), the microstructure, phases, micro-texture, and internal defects of SA L-PBF nickel-based superalloys were analyzed, and tensile and cutting-edge fatigue tests with stress ratios R =−1 and 0.1 were performed at 25 °C and 650 °C to investigate the fatigue failure behavior. The results showed that the SA treatment promoted microstructural homogenization with vague laser scanning tracks. The synergistic effect of the γ', γ'', and δ phases improved the mechanical and fatigue properties. Elevated temperatures and positive stress ratios promoted the occurrence of subsurface or internal failures. The four cracking modes include crack nucleation from the crystallographic facets, pore-assisted facetted crack nucleation, lack of fusion-induced crack nucleation, and inclusion-induced crack nucleation. At 650 °C, the grains fractured along the maximum shear plane, formed a large number of highly inhomogeneous facets, which caused significant fluctuations. Finally, the phase transition processes during SA treatment and defect-related fatigue failure mechanisms were elucidated. This study provides key quality and testing data to support the advancement of L-PBF nickel-based superalloys and provides a foundation for their optimized design and industrial applications.