Microstructure and tensile property of SLM 316L stainless steel manufactured with fine and coarse powder mixtures

Selective laser melting (SLM) technology is the prevailing method of manufacturing components with complex geometries. However, the cost of the additive manufacturing (AM) fine powder is relatively high, which significantly limits the development of the SLM. In this study, the 316L fine powder and coarse powder with a mass ratio of 80:20, 70:30 and 60:40 were mixed using a ball milling and the samples with a relative density greater than 97% were prepared by SLM. The results show that the intricate temperature gradients and surface tension gradients in SLM will produce Marangoni flow, forming a typical molten pool morphology, cellular and strip subgrain structures. And as the proportion of coarse powder increases, the scanning track morphology changes from smooth to undulating; the morphology of the molten pool and subgrain structure are weakened. Meanwhile, the unmelted particles appear on the surface of the SLM sample. On the premise of an introducing appropriate amount of large particle size powder (20%), the SLM samples still have good mechanical properties (662 MPa, 47%).