Effect of Scanning Process and Heat Treatment on Microstructure and Mechanical Property of Inconel 718 Fabricated by Selective Laser Melting

Inconel 718 (IN718) superalloy is extensively used in various applications owing to its excellent comprehensive property. Fabricating Inconel 718 (IN718) superalloy by selective laser melting holds great promise for producing complex aerostructure components. In this work, the influence of scanning strategies, laser power, scanning speed and hatch distance were revealed and compared. Further, different solution treatments at various temperatures for 1 h followed by a two-step aging at 720/620 °C were employed to improve the mechanical properties of as-built IN718 alloy. The microstructure, hardness and tensile behavior of the as-built and heat-treated samples were investigated, respectively. Results showed that designing scanning strategies by changing rotation angle between scanning tracks had a limited impact on the relative density of samples while influencing the hardness of the samples. The microstructure of the as-built IN718 was a mixture of columnar and equiaxial grains with γ matrix and Laves phase precipitates in the grain boundaries. After heat treatment, the columnar structure was converted into equiaxial grains, weakening the anisotropy in samples. Meanwhile, the dissolution of Laves phase and formation of fine γ′ and γ″ precipitates dispersively distributed in the matrix became more remarkable with increasing solution temperature. As a result, when solution-treated at 1000 °C, the hardness and tensile strength reached 450.52 HV and 1396.22 MPa, respectively, and such values were increased by 28.7 and 26.9% in comparison with the AMS 5662.