Laves phase morphology-mediated damage initiation and deformation heterogeneity mechanisms in laser directed energy deposited GH4169 superalloy

The inherent nonequilibrium solidification during laser directed energy deposition (L-DED) of GH4169 superalloy induces Laves phase precipitation, which acts as critical initiators for damage and exacerbates deformation heterogeneity. Resolving these morphology-mediated failure mechanisms is vital for guaranteeing the structural integrity of aerospace components under extreme service environments. In this study, by integrating advanced experimental characterization with a crystal plasticity-phase field model (CP-PFM), we systematically decode the quantitative relationships linking Laves phase morphology to damage initiation and deformation heterogeneity. The results demonstrate that controlled thermal processing transforms Laves phase characteristics from long-striped configurations to granular particles, reducing the stress concentration factor by 28 %. This morphological evolution alters the damage mechanism from phase fragmentation to interfacial debonding, effectively limiting crack initiation and propagation. Long-striped Laves phase exhibits a higher damage factor due to fragmentation, whereas the granular Laves phase transfers damage to the matrix because of debonding. The CP-PFM simulations further reveal that the Laves phase morphology alters the activation of dominant slip systems in the γ matrix, and granular Laves phases facilitate more stable plastic deformation by homogenizing strain partitioning. Simultaneously, the Laves phase dissolution promotes homogeneous precipitation of γ’/γ“ strengthening phases, with their average sizes increasing from 13.76/8.23 nm to 20.42/13.74 nm, thereby enhancing yield strength from 441 MPa to 1107 MPa. These insights provide a mechanistic foundation for optimizing microstructural design in additive manufacturing, ultimately contributing to superior mechanical performance and damage tolerance in applications.