Effect of Layer Directions on Internal Structures and Tensile Properties of 17-4PH Stainless Steel Parts Fabricated by Fused Deposition of Metals

Abstract

17-4PH stainless steel specimens were fabricated by fused deposition of metals (FDMet) technology, which combines 17-4PH particles with an organic binder. FDMet promises a low-cost additive manufacturing process. The present research aims to clarify the influence of layer directions in the 3D printing process on the mechanical and shrinkage properties of as-sintered and as-aged specimens. All specimens (the as-sintered and as-aged specimens printed in three layer directions) exhibited high relative density (97.5–98%). The highest ultimate strengths (880 and 1140 MPa in the as-sintered and as-aged specimens, respectively) were obtained when the layer direction was perpendicular to the tensile direction. Conversely, the specimens printed with their layer direction parallel to the tensile direction presented a low ultimate strength and low strain at breakage. The fact that the specimens with their layer direction parallel to the tensile direction presented a low ultimate strength and low strain at breakage is a usual behavior of parts obtained by means of FDM. The SEM images revealed oriented binder domains in the printed parts and oriented voids in the sintered parts. It was assumed that large binder domains in the filament were oriented perpendicular to the layer directions during the fused deposition modeling printing, and remained as oriented voids after sintering. Stress concentration in the oriented void defects was likely responsible for the poor tensile properties of these specimens.

A Review on Material Extrusion Additive Manufacturing of Metal and How It Compares with Metal Injection Moulding

“…The built orientation is an important issue that has been widely studied with three orientations, which are the flat, on-edge and vertical orientations. All available studies report that the vertical built orientation exhibits the lowest tensile properties due to layer delamination [8,53,56,64,68,81]. Figure 18 shows the difference in fracture surface characteristics and related failure mechanism of metal MEX specimen built by the flat (Figure 18a,c) and vertical orientations (Figure 18b,d).…”

“…The filament will be brittle if too-high solid loading is used [145]. Very careful handling of the filament is needed with an extra heater to reduce the brittleness of the filament and to reset the memory shape [56,64,146]. The filament must have no porosity, shape consistency and uniform distribution of the metal powder, including as high as possible of solid loading to minimise shrinkage [94].…”

“…The usage of high flexibility polymer as a part of the binder system, such as PA [29], PLA [51,89] and PO [37,96,102,168] can also be helpful. Otherwise, special features, such as a heating chamber, are required to reduce the brittleness of the filament during feeding [56,64]. For the well-known commercial filament; Ultrafuse 316L, the high flexibility of the skin case is utilised to enhance the filament flexibility [4].…”

“…The effect of solid loading content on the shrinkage of 17-4PH stainless steel [8,36,44,49,64,127,158] and 316L stainless steel [9,35,37,38,41,44,45,52,53,56,57,66,68,70,75,98,127,159] with different sintering conditions is summarised in Figures 15 and 16, respectively. The solid loading of 17-4PH is in the range of 55% to 79% with measured shrinkage of 12% to 20% [8,36,44,49,64,158], which is similar to the typical shrinkage obtained in MIM (12% to 20% [127]). Generally, it is observed that as the solid loading increases, the shrinkage tends to decrease.…”

“…It is found that neural network algorithms provide the highest accuracy, which can successfully predict dimensional variations and optimise the printing and sintering process parameters of the metal MEX parts [101]. [8,36,44,49,64,127,158].…”