Fatigue performance and DADT certification of powder-bed additively-manufactured Ti-6Al-4V: defect assessments, EIDS distributions, and inspection limits

icaf2023 Tracking Number 106

Powder-bed fusion additive manufacturing (PFB AM) of metals has reached an intermediate stage of technological maturity. Parts manufactured by PFB AM are considered by OEMs and end-users for a growing set of applications. To date, however, few of those applications have been fracture critical components due to uncertainties inherent in durability and damage tolerance (DADT) certification of AM metals. Certification considerations specific to AM include fabrication system-to-system variability, updates to hardware and build-parameter-sets that occur at a frequency similar to those for personal electronic devices and software, and difficulties in non-destructive defect inspections of complex geometries to name only a few. The US Air Force relies upon the Equivalent Initial Damage Size (EIDS) distribution to characterize the quality of an aircraft structure upon manufacture. Although several decades of experience with this approach inform certification of structural components produced by conventional fabrication modes (cast and wrought parts), there is to our knowledge currently no available published EIDS data for PBF AM metals. In this work we report on our measurements of EIDS distribution data for PFB AM Ti-6Al-4V. EIDS distributions are in development for several hundred fatigue samples across which fabrication modality (laser- vs. electron-beam energy source), sample inclination to the build direction, surface condition, heat treatment, and other variables are modified. To assess the nature of the crack-nucleating defect in a given specimen, and to relate its size to the measured EIDS value, a series of destructive and non-destructive characterization activities is undertaken, including computed tomography, profilometry, and serial sectioning, among others. The results are interpreted in a certification context by comparison with data developed in parallel for mill-annealed Ti-6Al-4V plate forgings.