Unveiling the temperature-dependent fatigue mechanisms of LPBF Inconel 718 with experiments and crystal plasticity simulations

Understanding the high-temperature fatigue behavior of additively manufactured nickel-based superalloys is essential for ensuring the reliability of aerospace components under extreme operating conditions. Despite extensive experimental efforts, the microstructure-dependent mechanisms governing fatigue at intermediate to high temperatures remain poorly understood. This study combines strain-controlled low-cycle fatigue experiments with crystal plasticity finite element (CPFE) simulations to elucidate the temperature-dependent deformation and damage evolution in laser powder bed fusion (LPBF) Inconel 718 (IN718). Specimens exhibited high densification and consistent tensile properties across all experimental replicates, indicating that fatigue response is dominated by intrinsic temperature-dependent microstructural mechanisms rather than processing-induced defects in this study. At 650°C, fatigue life drops significantly. Simulations and experimental mappings show that plastic deformation is restricted to a few interconnected slip systems. This causes extreme strain heterogeneity and stress accumulation at high Schmid factor gradient interfaces to trigger premature cracking. Conversely at 850°C, thermal softening promotes widespread uniform intergranular deformation. A dual fatigue indicator parameter analysis confirms the failure mode shifts from local stress-driven cracking accurately captured by the SWT parameter at 650°C to viscoplastic damage captured by accumulated plastic work at 850°C. This integrated framework provides vital mechanistic insights for designing durable additive manufacturing components.