Filament extrusion-based additive manufacturing of 316L stainless steel: Effects of sintering conditions on the microstructure and mechanical properties

Indirect Induction Sintering of Metal Parts Produced through Material Extrusion Additive Manufacturing

“…Several trapped pores are found inside the equiaxed grains after 240 s of the refractory-sintered samples, which is typical during the last stage of sintering [ 49 ]. Annealing twins are additionally identified during the grain growth of the vacuum-sintered specimens after 60 s, which has been reported previously during the grain growth of powder sintering FFF stainless steel 316 L [ 52 , 60 ]. Concerning the vacuum-sintered specimens, large dendritic grains are observed after 360 s, which is connected to the extended soak time compared to the refractory ballast sintered.…”

“…In a vacuum, the samples closer to the crucible will experience higher effective heat compared to those at the center of the crucible, but with the detrimental effect of having an uneven distribution of radiated heat along the sintered part if not symmetric along the crucible principal geometric axes. However, high densities of 99.9% and 99.8% are reached rapidly after 4 min and 6 min in the refractory ballast and vacuum-sintered specimens, respectively, being a notable improvement compared to the conventional furnace approach, which reached between 2 h and 13 h heating cycles in recent studies of sintered FFF stainless steel 316L [ 52 , 53 , 54 , 55 ].…”

Fatigue Behavior of Additively Manufactured Stainless Steel 316L

“…For FFF parts in [104], after parameter optimization throughout the entire SDS process, including printing and debinding, a final density above 95% of the theoretical density was reached. In [105], the highest relative density obtained was 92.9%, with little influence of layer orientation, whereas in [35], an average sintering density above 96% was reported. Overall the porosity of FFF is still higher than PBF and DED, in which case full densification can be achieved.…”

“…After filament deposition on a platform to allow shaping, the binder is removed in a debinding step, and the remaining material is sintered, similarly to BJ, with the advantage of low cost, anisotropy, and low health hazard. The use of FFF for 316L has been recently reported in [15,35,36].…”

“…For FFF technologies, the microstructure was investigated in [15], and X-ray Diffraction (XRD) data of the 316L sintered sample solely showed γ (FCC) austenitic phase with full dissipation of the subtle presence of δ-ferrite detected in the powder feedstock. In [35], the nanoindentation technique revealed instead the presence of austenite, δ-ferrites as well as detrimental oxides and σ-phase depending on sintering conditions. The presence of the second phase (Cr-C) along the grain boundaries was also noticed in [36].…”