Microstructural evolution and anisotropic mechanical properties of Inconel 625 superalloy fabricated by directed energy deposition

The microstructure and the anisotropy of mechanical properties for Inconel 625 superalloy prepared by directed energy deposition (DED) were investigated in this study. The microstructure of as-deposited sample was mainly composed of epitaxial columnar grains, which showed a z-shaped distribution along the deposition direction. Combined with thermodynamic calculation, the formation mechanism of Laves phase in as-deposited Inconel 625 superalloy was discussed in detail. Owing to the anisotropic microstructure of as-deposited sample, tensile properties and fatigue crack growth (FCG) behavior showed significant anisotropy. Compared to vertical sample, the grain boundary volume fraction in horizontal sample was larger, which caused that the ability of grain boundary strengthening and the resistance of fatigue crack growth were higher in horizontal sample during tensile and fatigue crack growth process. As a result, the yield strength and the ultimate tensile strength of horizontal sample were higher, while the fatigue crack growth rate was lower. However, the elongation of horizontal sample was smaller than that of vertical sample caused by the Laves phase distribution.