This study confirmed that Al₂O₃ particles were formed in IN718 alloys during the fabrication by both selective laser melting (SLM) and electron beam melting (EBM). Different heat pattern and atmospheres in SLM and EBM result in different distribution and volume fraction of Al₂O₃ particles. The Al₂O₃ oxides would act as nucleation sites for the precipitation of Nb/Ti carbides, leading to the formation of unique core-shell composites with Al₂O₃ in the center and Ti/Nb at the periphery. In order to investigate the oxygen content introduced during SLM and EBM, the volume fraction of Al₂O₃ formed in spark plasm sintering (SPS)-fabricated substrate, by consolidating the pre-oxidized IN718 raw powders at 800 °C, was utilized. The oxygen contents introduced to IN718 substrates during SLM and EBM fabrication were calculated to be 0.030 wt% and 0.099 wt%, respectively.