Effects of cooling conditions on the shape, microstructures, and material properties of SS308L thin walls built by wire arc additive manufacturing

Abstract

This research explores the effects of the free cooling and active cooling on the surface roughness, microstructures, and material properties of SS308L walls manufactured by wire arc additive manufacturing (WAAM). In the free cooling, a holding time of 30 seconds was used between two successive layers to cool down the wall by the natural air. On the other hand, in the active cooling, the compressed dry air was used for rapidly cooling the wall between two adjacent deposits. The results show that the walls built with the active cooling exhibits lower surface roughness and higher layer thickness when compared to those of the walls built with the free cooling. In both cases, the microstructure evolution of the walls is similar. A specified layer in the middle of the walls displays columnar dendrites of austenite growing vertically along the building direction and residual ferrite remaining in the boundaries of austenite. However, the spacing of secondary dendrite arms in the walls built with the active cooling is smaller, leading to a significant increase in microhardness and tensile strengths.