Process Parameters Control Fatigue Performance in AM Superalloys

The Challenge

Inconel 718 is the workhorse superalloy for aerospace turbine components, where very-high-cycle fatigue performance is non-negotiable. As laser powder bed fusion scales toward production of these safety-critical parts, manufacturers face an overlooked variable: the choice of shielding gas. Argon and nitrogen both prevent oxidation during printing, but their effects on long-term fatigue life remained poorly understood.

The Solution

This research compared L-PBF IN-718 produced under argon versus nitrogen shielding, characterizing defects via optical microscopy, Archimedes density, and X-ray CT, then subjecting specimens to VHCF testing at 20 kHz. The results revealed a critical tradeoff: nitrogen shielding produced finer grain structure but introduced more porosity and inclusions. These defects became crack initiation sites, degrading fatigue performance despite the microstructural refinement.

Argon-shielded specimens showed narrower fatigue life scatter and different failure mechanisms—cracks initiated from microstructural features rather than defects, leaving characteristic facets at initiation sites.

Results

The study demonstrates that process gas selection directly impacts fatigue reliability in AM superalloys. For fatigue-critical aerospace applications, argon shielding delivers more consistent performance. This finding gives manufacturers a concrete process parameter to control when qualifying L-PBF IN-718 for turbine components where billion-cycle durability is required.