Strain and Microstructural Evolution in Architected Lattices: A Comparison of Electron Beam and Laser Powder Bed Fusion

Metallic microlattice (MML) materials enable novel material properties through geometry and topology, and through additive manufacturing (AM) there exists a viable and scalable method of producing the fine networks of struts and nodes which make up an architected lattice. However, AM methods often induce locally high cooling rates, which lead to residual strains and anisotropic microstructures which can limit how tunable and predictable the properties of a lattice will be across its volume. Residual strains can degrade mechanical properties or act as strain concentrators and contribute to the failure dynamics of a lattice under load. In the micron scale regime of lattices this means the microstructure is the point of failure minimization, and we show that the orientation of a strut between two edge cases within a lattice and its proximity to a heatsink will change the strain distribution and microstructure within a lattice strut depending on the manufacturing technology used. We show that changes in energy density and solidification conditions between two AM methods, laser and electron beam powder bed fusion (PBF-LB and PBF-EB) lead to different magnitudes of residual strain and anisotropy, with PBF-EB showing far lower levels of residual strain and greater consistency in both strain and microstructure invariant of strut orientation next to a heatsink.