Tailored microstructure by using in-situ re-scanning and its influence on fatigue crack growth behavior of Inconel 718 fabricated by LPBF at elevated temperature

Owing to the basic layer-by-layer laser powder bed fusion (LPBF) process, defects will be inevitably present in specimens and can affect their material properties. In-situ re-scanning can be used to fabricate high-quality key components in small batches, which can effectively eliminate the pore defects generated in LPBF. In this study, the effect of in-situ re-scanning on the tailored microstructural characteristic of Inconel 718 was investigated. After in-situ re-scanning, dynamic recrystallization occurred, Laves precipitates displayed low sizes, and the grains were effectively refined. Besides, the results showed that the melt pool boundary (MPB) acted as a guide to the propagation of fatigue cracks. In the case of vertical forming, complex grain boundaries due to grain refinement caused by in-situ re-scanning, resulting in a significant improvement in FCG resistance. In the case of horizontal forming, however, in-situ re-scanning weakened this resistance instead. Although the refinement of grains by in-situ re-scanning was not significant, the size of Laves precipitates was reduced, which in turn reduced the hindrance to FCG. In addition, the effects of MPBs, micro precipitates, and grain boundaries (GBs) on the FCG behavior were discussed in comparison. This study provides a theoretical basis for fabricating higher-performance LPBF specimens.