Investigation of the effects of deposition scan patterns on STS 316L thin-wall structures in directed energy deposition

This study investigates the effects of deposition scan pattern on the fabrication of thin-wall structures using laser powder directed energy deposition (LP-DED). Two distinct deposition patterns-sequential (SP) and center-out (COP)-were evaluated in terms of their influence on bead formation, thermal behavior, and mechanical properties. The sequential pattern resulted in significant asymmetry in bead shape and a greater temperature gradient, while the center-out pattern achieved a more balanced flow, leading to more uniform bead formation. Experimental results showed that the center-out pattern minimized distortion, with a maximum deviation of 0.2 mm for a thin-wall structure of 100 mm in height, compared to the sequential pattern with a maximum deviation of 5.5 mm. Electron backscatter diffraction (EBSD) analysis further revealed that the grain size in the COP method was approximately 40% smaller than that in the SP method, and the primary dendrite arm spacing (PDAS) was 25% smaller, resulting in a more refined microstructure. As a consequence, the COP method led to a 4.9% increase in hardness and achieved a higher density of 99.9% compared to 99.7% in the SP method. This study highlights the importance of choosing an appropriate deposition scan pattern for improving the quality of thin-wall structures fabricated by DED, offering insights into reducing deformation and optimizing microstructure and material properties.