The surface quality, microstructure and properties of SS316L using a variable area scan strategy during quad-laser large-scale powder bed fusion

In this work, a self-developed muti-laser powder bed fusion (ML-PBF) equipment was utilized to produce a series of SS316L samples. A new scan strategy called "variable area scan" was used to investigate the dimensional accuracy, microstructure, defects, surface roughness and mechanical properties of the single-laser PBF samples, dual-laser PBF samples and quad-laser PBF samples during muti-laser PBF processing. It is found that single-laser samples and quad-laser samples have got a good surface quality and dimensional accuracy, but the size of the double laser printed samples have large deviation due to the stitching error. The OM and SEM diagrams show the complex interlacing of the melt tracks in the multi-laser junction area, and the existence of holes at the lap boundary, which is also one of the reasons for the unstable microhardness of the overlap region. As the number of lasers increases，the grain size of the region increases, and the preferred orientation of the overlapping region changes and exhibits a pronounced <100> texture, and more columnar grains along BD are generated because of a high thermal gradient. Moreover, dual-laser PBF samples even get better average tensile properties than that of single-laser PBF samples. The work can provide a practical reference for the large-size parts building during the muti-laser PBF processing.