Material characterization study of laser powder bed fusion type 316L stainless steel with process parameter modifications to promote isotropy

Specially processed type 316L stainless steel fabricated via laser powder bed fusion (L-PBF) exhibits a substantial reduction in anisotropy characterized by directionally dependent properties and microstructural features. To promote isotropy, standard electro optical systems (EOS) deposition process parameters were modified by increasing the laser scan speed. With all other parameters constant, an increased scan speed reduces the thermal energy input, causing deliberately inserted lack-of-fusion (LOF) defects aimed at tailoring the microstructure and properties. As material is deposited and rapidly solidifies layer by layer, multidirectional growth of cellular colonies breaks down as the most favorable orientation outpaces its neighbors. Each LOF pore halts the continuation of the fastest growing colony and reinitiates multidirectional growth from its free surface. After a hot isostatic press treatment, the pores consolidate, and cellular boundaries annihilate to form a lower aspect ratio and smaller grains with a more uniform texture than seen in standard processed L-PBF material. This process-structure relationship was also seen as a convergence of strength and impact energy in all directions examined. Although additional testing and optimization would be necessary, this first trial concludes that deposition parameter modifications will greatly improve isotropy in L-PBF materials.