Dynamic mechanical behavior and microstructural evolution of additively manufactured 316L stainless steel

The high strain rate dynamic behavior of additively manufactured (AM) 316L stainless steel (SS) is investigated, and a dynamic deformation-induced microstructural evolution is examined in this study. First, the as-built microstructure feature is characterized. The grain morphology is revealed to be location-dependent and driven by the solidification process. A steep rise in the point-to-origin misorientation profile traversing a melt pool boundary is observed, quantitatively describing the influence of process-induced interface on the initial grain orientation state. The static and dynamic mechanical properties are then examined. Compared with conventional wrought 316L SS, AM 316L SS demonstrates an enhanced mechanical strength under quasi-static compression (with a \({\sim }\,95\%\) increase in yield strength). Under dynamic shearing, strain rate-induced strength enhancement is observed in wrought 316L SS (with a \({\sim }\,47\%\) increase in dynamic flow stress); AM 316L SS nevertheless demonstrates nearly rate-insensitive responses in its yield stress (with a \({\sim }\,5\%\) increase in dynamic flow stress). Localized deformation in the form of an adiabatic shear band and the associated structural evolution are analyzed. Radical changes in crystallographic and structural features induced by high strain rate deformation are observed. Grain deformation and rotation lead to a remarkable difference in the grain orientation and spatial direction from the starting state driven by the solidification process. Upon dynamic shearing, the transmission of localized plastic deformation across melt pools is revealed, and the indication in grain rotations is discussed. The change in the geometrically necessary dislocation density is examined, hinting at the competition of the dislocation multiplication and annihilation under localized deformation. The current work enriches the understanding of the dynamic mechanical properties of AM materials at high strain rates.