Remelting-based microstructure engineering in laser powder bed fusion: A case study in 316L stainless steel

In laser powder bed fusion (LPBF), the formation of bulky columnar grains often results in undesirable mechanical anisotropy. Here, we demonstrate a new strategy to control the microstructure in LPBF through tuning melt pool overlaps without changing energy densities and scan patterns. Using 316L stainless steel as an example, we generate a wide range of grain sizes and morphologies. The underlying mechanism is associated with the retainment or elimination of newly nucleated grains at a melt pool during the formation of subsequent melt pools. The propensity of retainment or elimination of grains is largely dependent on the extent of melt pool overlaps because the grains are prone to nucleate at the free-surfaces of melt pool boundaries. This facile strategy could be applicable to a wide range of metallic alloys, paving a new way for microstructure engineering in additive manufacturing.