A novel end-to-end integrated process paradigm for fatigue life improvement in nickel-based superalloy hole structures

Abstract

The premature fatigue failure of hole structures poses a critical challenge in aviation components. This study introduces an end-to-end integrated paradigm, utilizing the cold expansion process (CEP) as a technological carrier to simultaneously improve both fatigue life and stability in the IN718 hole structures. Integrated process technology gains better performance than the isolated ones, where IP-CEP achieves a 2.76-fold improvement in fatigue life. This paradigm further advances to a 4.87-fold fatigue life improvement with reduced dispersions by actively integrating drilling, reaming, cold expansion, reaming, and polishing, breaking through the upper limits of CEP-series. The fatigue life improvement mechanisms are elucidated through advanced surface integrity analysis and fatigue fracture characterization. The results show that the cold expansion process induces substantial maximum compressive residual stress (CRS) and gradient plastic deformation layer, while reaming and polishing effectively improve the surface quality of cold expansion holes. Finally, a clear link between surface integrity and high-temperature fatigue life is established. The consistent enhancement in the fatigue life of the hole structure was primarily attributed to the synergistic effects of CRS, the plastic deformation layer, and superior surface quality. This study proposes an active anti-fatigue paradigm with flexible stages, providing a unified framework to balance multiple objectives for high-temperature structural applications.