Impact of high-productivity process parameters in powder bed fusion – laser beam on microstructure of stainless steel 316L

Abstract

Abstract Low production speed is a limiting factor for wider adoption of Powder Bed Fusion – Laser Beam (PBF-LB). The build rate can be increased by scaling up main process parameters, i.e., layer thickness, scan speed, and hatch distance. However, increased build speed leads to low quality in terms of density, surface finish, and mechanical properties. This study analyses size, orientation, and shape characteristics of 316 L with three- and four-factor increases in hatch distance and layer thickness beyond the state of the art to 270 and 80 µm. I-optimal designs were employed to create empirical models relating porosity level and processing parameters. The influence of overlapping melt pools on aspect ratio, size, and orientation of the pores were elucidated by analysis of optical micrographs of etched cross-sections. The lack-of-fusion pores generated by high layer thicknesses and hatch distances are preferentially orientated with respect to the build direction. With given layer thickness, the porosity level abruptly increases at a threshold of hatch distance, exceeding 1% areal fraction by 2D image analysis. Within the experimented region, the maximum allowable hatch distance for achieving <1% porosity decreased from 200 to 160 µm as the layer thickness increased from 20 to 80 µm.