Influences of the compressed dry air-based active cooling on external and internal qualities of wire-arc additive manufactured thin-walled SS308L components

Abstract

Among additive manufacturing (AM) technologies, wire-arc additive manufacturing (WAAM) features a high material deposition rate and low costs of device investment. However, WAAM parts generally undergo a complex-thermal history and a high accumulation of heat, which significantly influences its external and internal qualities. In this article, the influence of different cooling conditions on the qualities of WAAM SS308L components was addressed. Three thin walls were built by WAAM with three cooling conditions. The first and second walls were produced with the free-cooling condition, where an interlayer holding time (Tih) of 30 s and 60 s was used between two successive deposits, respectively. The third wall was built with the compressed dry air (CDAir)-based active cooling, in which the compressed dry air (CDAir) and an interlayer holding time of 10 s were employed between two adjacent layers to cool down the workpiece. The obtained results indicate that the evolution of microstructures in three walls is very likable. In the bottom and the middle regions, the microstructure mainly contains vertically oriented dendrites of austenite and ferrites that appear in the austenite grains’ boundary. The austenitic phases also appear in equiaxed grains in the top region. However, the CDAir-based active cooling has noticeable effects on the spacing of secondary dendrite arms (SSDA) in the middle of the walls. The wall built with the CDAir-based active cooling features the smallest average SSDA, followed by the walls produced in the free cooling condition and a Tih of 60 s and 30 s, respectively. Accordingly, the CDAir-based active cooling produces the highest average hardness and tensile strengths. Moreover, the wall produced using the CDAir-based cooling also reveals the lowest surface roughness. Therefore, it can be considered that the CDAir-based active cooling is a reasonable option to enhance the internal and external qualities of WAAM stainless steel 308L components.