On the role of dynamic grain movement in deformation and mechanical anisotropy development in a selectively laser melted stainless steel

316 L stainless steel samples were built vertically (VB) and horizontally (HB) by selective pulsed laser melting. The microstructure of the as-fabricated samples was investigated using a range of characterisation techniques and the properties evaluated by tensile testing. It was found that at a relatively low laser power (200 W) pores evolved from lack-of-fusion pores to keyhole pores with increased laser exposure time. Correspondingly, the porosity level decreased first and then increased with exposure duration. Increased laser power led to minimisation of porosity. The porosity type and level did not cause significant influence on tensile properties in the current case. With increased energy density, the microstructure changed from a fine dispersive fan-like grain structure gradually into a coarse vertically grown columnar grain structure, leading to increased <100> texture along the building direction. With the latter microstructure, the VB samples show much higher yield strength and ultimate tensile strength but lower elongation than their HB counterparts, leading to development of mechanical anisotropy. The mechanical anisotropy was strongly associated with grain movements through different dominant deformation mechanisms in different building directions, i.e., the VB samples deformed mainly by grain elongation via dislocation slipping whereas the HB samples deformed by grain rotation through massive twinning and slipping. With the refined fan-like grain structure, grain rotation was heavily involved in both HB and VB samples, which was beneficial for reduction in mechanical anisotropy. The extent of mechanical anisotropy decreased with decreased laser power and exposure time, paving the way for reducing mechanical anisotropy in this material.