In-situ X-ray computed tomography study on defect evolution in additively manufactured GH4169 superalloy during high-temperature fatigue

This study investigates the defect evolution mechanisms in nickel-based GH4169 superalloy fabricated using selective laser melting (SLM) under high-temperature fatigue. X-ray computed tomography (CT) was employed for three-dimensional defect characterization, and in-situ fatigue tests were conducted at 400°C. Initial defects were found to be randomly distributed, primarily consisting of pores and lack-of-fusion (LOF) defects, with 80% having an equivalent diameter smaller than 20 μm. Pores exhibited significant axial elongation during fatigue loading in stress-concentration regions, especially at elevated temperatures, where localized plastic deformation was enhanced. Additionally, fatigue cycling led to defect coalescence, with smaller defects merging into larger ones, primarily along the tensile loading direction.