High-power laser powder bed fusion of 316L stainless steel: Defects, microstructure, and mechanical properties

Abstract

Low build rate has always been the bottleneck problem of the application and development of laser powder bed fusion (LPBF) metal 3D printing technology. Although increasing laser power has been an effective way to break through this technical problem, studies regarding the high power LPBF (HP-LPBF) are still insufficient. Relying upon a self-developed 2000 W level HP-LPBF equipment, this paper investigated the defect characteristics, microstructure, and mechanical properties of 316L stainless steel (SS) LPBF samples fabricated at three different laser power levels (200 W, 1000 W, 2000 W). The results show that hot cracks extending along high angle grain boundaries may form at 1000 W and 2000 W. However, no crack is observed at 200 W. With the optimized process parameters, highly dense (relative density>99.5 %) samples can be obtained at all three laser powers. Moreover, the build rate of the dense sample increases monotonously with the increase of laser power, which are 5.76 cm3/h at 200 W, 36 cm3/h at 1000 W, and 61.2 cm3/h at 2000 W. The dominant grain structures of all the as-built samples are columnar grains growing along the build direction. With the increase of laser power, the columnar grains become coarser in size and higher in proportion, the 〈001〉 texture gets stronger, while the dislocation density decreases slightly. Although the Vickers hardness and room-temperature tensile properties of the LPBF samples fabricated at 1000 W and 2000 W are slightly lower than those of the samples fabricated at 200 W, they are significantly higher than those of 316L SS forgings (ASTM A182M-2016A).