Novel strengthening mechanism of laser powder bed fusion-manufactured Inconel 718: Effects of customized hierarchical interfaces

A novel strengthening mechanism involving hierarchical interfaces self-assembled and/or artificially introduced into Inconel 718 (IN718) via laser powder bed fusion (PBF-LB/M) additive manufacturing (AM) has been discovered for the first time. The structures processed by applying two different scanning directions depending on the region have customized hierarchical interfaces that are formed by self-organization of the microscale lamellar structure comprising distinctively different crystal orientations and artificial control of local texture for mesoscale building blocks. The underlying mechanism of strengthening of the structures is clarified using experimental and numerical approaches. Numerical crystal plasticity finite element analysis successfully reproduces the experimental deformation behavior, including the stress-strain curves and anisotropic changes in the shape of the structures, revealing improvements in the mechanical properties by mechanical interaction owing to plastic anisotropy of the lamellar structure. A systematic numerical analysis of the deformation behavior of structures with a higher density of mesoscale interfaces between regions with different local textures suggests possible improvements in the mechanical properties, showing a 13 % increase in 0.2 % proof stress in the optimum structure. Additionally, excellent peak mechanical properties are observed owing to the competition of mechanical interactions between regions with different local textures and a decrease in plastic anisotropy owing to the activation of additional slip modes of the lamellar structure.