Precipitate-dominated crack initiation and propagation mechanisms in superalloy IN718 investigated via quasi-in-situ uniaxial tensile 3D imaging

Quasi-in-situ tensile three-dimensional imaging was employed to systematically investigate the crack initiation and propagation mechanisms of IN718 alloy in large aerospace precision castings at different locations and after HIP treatment under room-temperature uniaxial tension. Particular emphasis was placed on the influence of the precipitate–micropore system, precipitate morphology, and their three-dimensional spatial distribution on crack evolution. The results indicate that rapid cooling promotes preferential crack initiation through network-like Laves phase and carbide precipitates, whereas slow cooling produces granular, discretely distributed precipitates that reduce local strain sensitivity. HIP treatment markedly decreases the Laves phase content, effectively suppressing crack initiation. Dislocations tend to accumulate at precipitate interfaces, inducing local stress concentrations and intra-precipitate cracking; micropores evolve into planar fracture surfaces under stress, and cracks may propagate along non-crystallographic paths due to branching or local stress perturbations. Crack propagation is strongly governed by elongated precipitates and element segregation networks. High-density microcracks with short nearest-neighbor distances substantially enhance crack coalescence, ultimately interacting with micropores to form the main crack. Quantitative analysis reveals that microcracks in regions with KDE > 14 and KNN < 0.1 exhibit the highest probability of coalescence, decisively influencing main crack paths. This study highlights the critical role of the precipitate–micropore spatial architecture in directing crack propagation and provides essential insights for predicting the fracture and failure behavior of IN718 alloy in key aerospace engine components.