Process porosity and mechanical performance of fused filament fabricated 316L stainless steel

Abstract

Purpose This study aims to investigate the correlation between build orientation characteristics, part porosity and mechanical properties of the fused filament fabrication (FFF) process to provide insight into pore formation mechanisms and to establish guidelines for optimal process configurations. Design/methodology/approach Micro computed tomography and metallographic sections provide the basis for a correlation between porosity and extrusion path. Using the correlations found in this study, the way to improve printing strategies and filament properties can be deduced directly from an analysis of the print path and the final influence on mechanical performance. Findings With metal-FFF 3D printing technology, near-dense parts (0.5 Vol.%) can be fabricated. The pore architecture is strongly connected to the build direction and print strategy with parallel, elongated pore channels. Mechanical values of FFF samples are similar to metal injection-molded (MIM) parts, except the elongation to fracture. The high difference of yield strength of sintered samples compared to laser powder bed fusion (LPBF) samples can be attributed to the finer grains and a Hall–Petch hardening effect. The conclusions derived from this study are that the presented process is capable of producing comparable part qualities compared to MIM samples, with higher build rates in comparison to LPBF processes. Originality/value 316L stainless steel was successfully manufactured via FFF. This paper also addresses the effects of scanning strategies on the resulting porosity and proposes improvements to reduce residual porosity, thus increasing the mechanical performance in the future.

Optimization of the 3D Printing Parameters for Tensile Properties of Specimens Produced by Fused Filament Fabrication of 17-4PH Stainless Steel

“…Some pores due to the printing strategy (i.e., places where two perimeters joined or where the infill started and jointed) are visible in Figures 6a,b, and they are marked by dotted lines. This alignment of pores was observed in CT (Computed Tomography) scans of specimens produced by FFF with other highly filled filaments [21], and they can lead to weaker mechanical properties (see Section 3.3).…”

Influence of the Infill Orientation on the Properties of Zirconia Parts Produced by Fused Filament Fabrication

“…In those areas, some of the pores are round, while some others are elongated and adopt an elliptical shape. For the areas corresponding to the infill of the specimens, it is difficult to determine which of the pores are inside the extruded roads and which are the pores commonly seen in the gaps between roads [ 8 , 14 ].…”

“…The feedstock is a multicomponent polymer system highly filled with powder of the desired ceramic material [ 9 , 11 , 12 , 13 ]. Once the so-called green parts are shaped by FFF, the polymer components are removed in the debinding stage by a catalytic reaction [ 14 ], dissolution in a solvent [ 12 , 15 , 16 ] and/or thermal decomposition [ 9 , 17 , 18 , 19 ]. Finally, the parts are sintered to obtain nearly dense components.…”

“…In FFF and the other MEX techniques [ 8 , 14 , 31 , 32 , 33 , 34 , 35 , 36 ], the generation of the shape by the extrusion of material strands, known as roads, can result in defects in the gaps between the strands or weak areas if the bonding between the strands is not sufficient [ 8 ]. In early investigations, different solutions were proposed to reduce these defects [ 8 , 10 , 37 ].…”

“…In most cases, one or more perimeters are included in each layer following the contour of the part to improve the surface quality, and a raster fill pattern is used in the inner part of the specimens, known as the infill. The orientation of the roads in the infill of the parts is known to have a substantial effect on the properties of polymeric components produced by FFF [ 37 , 39 , 40 ], and the first studies for metallic FFF components showing similar effects are also available [ 14 ]. In the case of FFF ceramic components, the infill orientation is known to have a small effect on the dimensional variations during debinding [ 17 ].…”