Influence of remelting sequence on defect generation and high-temperature mechanical properties in laser powder bed fusion of IN718 alloys

The laser multiple melting strategy is commonly employed in the laser powder bed fusion (LPBF) process to reduce porosity levels and optimize mechanical properties. However, the influence of the temporal sequences of energy input has received limited attention, despite their potential to control defect generation and microstructure evolution. Therefore, in this work, two specific remelting sequences were investigated, referred to here as the preheating strategy (a low-energy first scan followed by a high-energy second scan) and the remelting (a high-energy first scan followed by a low-energy second scan) strategy. The findings indicated that defect generation and surface roughness are highly sensitive to variations in the remelting sequences, demonstrating that samples subjected to the remelting strategy exhibit significantly lower porosity levels. The simulations revealed that the defects in the preheating strategy originate from insufficient melting between layers and rough top surfaces caused by inadequate melt pool flow. Additionally, the samples subjected to the remelting strategy exhibited superior high-temperature mechanical properties, with an ultimate tensile strength of 959.7 MPa, yield strength of 792.0 MPa, and outstanding elongation of 23.1 % along the building direction after heat treatment. This enhancement was attributed to the increased geometrically necessary dislocation density induced by fine carbides measuring 0.9 mu m. This study offers valuable insights into the laser multiple melting process, providing a foundation for future research aimed at optimizing mechanical properties in the LPBF process.