Microstructure characteristics and mechanical behaviour of a selective laser melted Inconel 718 alloy

In this study, an Inconel 718 alloy was prepared by selective laser melting (SLM) with a pre alloyed powder, and the microstructure and mechanical behaviour of the fabricated parts were studied. First, the settled layer structure, composed of several interlaced Perlagemolten pools and molten channels, was captured by low-magnification optical microscopy (OM), and the formation mechanism was revealed by the Gaussian heat source distribution characteristics of the laser source used for the SLM fabrication. Second, high-magnification scanning electron microscopy (SEM) captured the different crystal structures in different fabricated positions; meanwhile, the cross-border growth phenomenonalong the forming direction and the growth and distribution characteristics of the crystalin the radial direction (perpendicular to the forming direction) were also captured. By introducing the component super-cooling theory, the growth mechanism of crystal structures in different positions under a multi-dimensional temperature gradient heat conduction coupling mode is proposed. Finally, combined with transmission electron microscopy (TEM) and a mechanical properties test, it was found that the mechanical properties were between those of parts fabricated by casting and those by forging because the gamma phase and y' phase were distributed in the crystal, while the carbide phase and Laves phase were distributed in the intercrystal region. (C) 2019 The Authors. Published by Elsevier B.V.