Microstructure-sensitive fatigue short crack and fatigue life of nickel-based superalloy welded joint

Welded components are widely used in advanced industries, but the complex non-uniform microstructure of welded joints poses challenges to accurately elucidate fatigue failure mechanisms and predict the fatigue crack initiation life of welded structures. Herein, we explore the fatigue short crack growth behavior in the fusion zone of nickel-based superalloy welded joints at 600 °C using an in-situ fatigue testing device. The microstructure-sensitive life of welded joints is predicted by dislocation-based crystal plasticity modeling that explicitly incorporates the experimentally characterized secondary phases. It is found that the short crack path is surrounded by multiple distinct activated slip plane traces (predominantly along {111} slip planes) and non-octahedral {110} slip planes are notably activated under high-temperature conditions. This pronounced multi-slip activity makes the crack growth deviate from the directions of a specific set of activated slip plane traces, leading to a complex zigzag-like cracking morphology. Geometric compatibility factor analysis reveals that local crack deflection at grain boundaries is strongly governed by the crystallographic orientation of neighboring grains. Furthermore, based on the crystallographic information and precipitate phase distribution from microstructure characterizations, we predict fatigue crack initiation life of the welded joint by dislocation-based crystal plasticity finite element model (CPFEM) that integrates Tanaka–Mura model. The predicted life is in good agreement with the experimental ones, falling into a two-fold scatter band. Our study could favor the analysis of fatigue failure mechanism and the prediction of fatigue crack initiation life of welded joints to provide guidance for improving service life of welded structures.