Fabrication of architecturally designed steel for improving isotropy of mechanical properties using directed energy deposition

Abstract

As an excellent illustration of architectural alloy designs, multilayered structures, which incorporates highstrength and high-ductility alloys in their layered composition, can accomplish unusual combinations of strength and ductility. This is possible because the continuous microstructure consisting of a single phase without a phase boundary in each layer results in a uniform distribution of strain. However, the multilayered structure shows anisotropic mechanical properties due to discontinuity from the phase boundary in the perpendicular direction (z-direction). In this work, an alloy system with a 3D continuous microstructure with two distinct steels was manufactured using laser-based directed energy deposition. The alternately deposited lines of two distinct alloys, along with the rotated consecutive layers, contribute to creating a woven-like structure. This architectural structure features continuous microstructures in multiple directions. Successfully manufactured both multilayered and woven-like systems demonstrated advanced yield strength and uniform elongation compared to each constituting alloy in the xy plane. In the z-direction, however, only the woven-like system exhibited improved properties as in the xy plane; the multilayered system did not. This isotropy in the mechanical properties of a woven-like system results from a 3D continuous microstructure in the z-direction. The strain analyses confirmed the deformation of the brittle body-centered cubic phase and partitioning to the ductile phase which are key mechanisms of mechanical property enhancement with continuous microstructure.