Enhanced strength and delayed necking of architected metametals additively manufactured via laser sheet fusion

Abstract

Using a pulsed laser to sequentially weld and cut SS304L sheets, novel metametals with sharp transitions in macrophases (regions with distinct microstructure, morphology and properties) were additively manufactured. By modulating the laser pulse parameters, the macrophases could be made strong via high dislocation densities (0.2 %YS ∼ 660 MPa; %EL ∼ 22 %) or ductile via transformation-induced plasticity (TRIP) effects (0.2 %YS ∼ 535 MPa; %EL ∼ 36 %). By passing over selective regions during welding, the original work-hardened microstructure and properties of the metal feedstock sheets can also be retained (0.2 %YS ∼ 970 MPa; %EL ∼ 19 %), greatly raising the overall in-plane strength of the metametals (up to 0.2 %YS ∼ 840 MPa; UTS ∼ 975 MPa). Importantly, the metametals exhibited delayed necking at strains up to 2.3 × as high as that of their constituent macrophases. This was due to the enhanced work hardening rate conferred by the TRIP macrophases and the formation of self-stabilizing interfacial shear stresses, which worked together to arrest strain localizations that could lead to the early onset of necking. As a result, the strength-ductility tradeoff curve of the metametals surpassed that of SS304L reported in the wider literature.