As-built surface layer characterization and fatigue behavior of DMLS Ti6Al4V

Direct Metal Laser Sintering (DMLS) is a powder bed fusion technology used in the fabrication layer-by-layer of metallic parts directly from a CAD file. Since the fatigue behavior of DMLS Ti6Al4V is strongly influenced by the surface roughness of the as-built surface, fatigue tests were performed on smooth specimens produced with different orientations with respect to build using an EOS M 290 system. A SEM investigation and roughness measurements of the test surfaces were used to interpret the surface roughness as the contribution of i) roughness induced due to solidification of the melt pool (primary roughness); ii) roughness induced by partly melted powder particles (secondary roughness). Surface roughness modification from the as-built state by manual grinding was also investigated in fatigue and found to give a limited improvement. On the other hand, surface machining improves considerably the fatigue strength with respect to both the as-built condition and the manually ground condition.