A critical insight into lack-of-fusion pore structures in additively manufactured stainless steel

Despite the obvious advantages of additive manufacturing (AM) in producing metallic parts, defect formation remains a challenge that deleteriously impacts some critical materials properties of AM parts. Here, through electron microscopy and X-ray computed tomography (X-ray CT), new insights are revealed about lack-of-fusion (LOF) pores; the most common defect reported for AM. We show that LOF pores are not simply a void but a complex structure comprising oxide films decorating pore walls and grain refined regions with dislocation structures surrounding the pore. The formation of a thin nanocrystalline metallic layer on the pore wall is also observed. Spatter particles are the source of most LOF structures at high densities typical of recommended processing conditions and can only be eliminated by careful selection of processing parameters. Data constrained modelling, which uses the materials’ properties, was used for generating 3D representations of the complex structure surrounding LOF pores from X-ray CT datasets. • X-ray CT studies of lack-of-fusion (LOF) pores in 316SS made by laser powder bed fusion (L-PBF) were made. • LOF pores can be classified into different groups depending on their origin. • LOF pores caused by spatter particles persist even in materials with high density. • These pores have affiliated oxide and dislocation structures and internal nanoscale metal layer. • Lack-of-fusion pores cannot be considered as only void structures.