Microstructural control of LPBF Inconel 718 through post processing of intentionally placed AM discontinuity distributions

A major untapped potential of laser powder bed fusion (LPBF) is the ability to additively manufacture (AM) parts with site-specific properties. However, robust methods of improving performance and manufacturing efficiency via spatial variations in microstructure are underexplored. This work introduces a method of creating several distinctive multi-modal microstructures in the nickel superalloy, Inconel 718, by performing a Hot Isostatic Pressing (HIP) procedure on characteristic LPBF discontinuities such as keyhole and lack of fusion (LOF) porosity, as well as large powder filled voids. Observed using electron backscattered diffraction, this approach enables the formation of site-specific variations in microstructure and extreme bi-modal microstructures. Processing AM parts via this method facilitates the production of fully dense, equiaxed, and strain free, material culminating in a 47% time saving per layer. In addition to this, it is proposed that the use of lack of fusion / HIP processing in AM has the potential to enable the manufacture of dense components using otherwise difficult to process materials.