Revealing the Pore Formation Mechanisms During Laser Powder Bed Fusion Additive Manufacturing of Hastelloy X via In-Situ Ultra-Fast Synchrotron X-Ray Imaging

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Abstract
During the Laser Powder Bed Fusion (L-PBF) process, the occurrence of defects such as cracks and pores significantly reduces the mechanical properties and service life of the parts. Therefore, in-depth research on the non-equilibrium metallurgical processes in L-PBF is of great importance. In this study, utilizing synchrotron radiation X-ray imaging technology, we investigated the formation and movement mechanisms of pores in Hastelloy X during the L-PBF process. By adjusting processing parameters, we observed the pore behaviour within the molten pool under different keyhole modes and identified that higher laser power deepens the vapour depression, while higher scanning speed generally yields a shallower, more stable keyhole by reducing keyhole-wall oscillations. The study further confirmed three types of keyholes formed under different process parameters, along with their corresponding pores distribution characteristics. By tracing pores, we revealed the melt pool flow dynamics within the Hastelloy X melt pool during L-PBF. The observational results and schematic diagrams of the two-dimensional keyhole model presented a solid theoretical basis and practical reference for optimizing L-PBF process parameters by linking keyhole morphology or stability (depth and oscillation) with pore formation, escape, and entrapment, thereby reducing porosity and enhancing material density and component performance.