On the Microstructures and Fatigue Behaviors of 316L Stainless Steel Metal Injection Molded with Gas- and Water-Atomized Powders

Abstract

316L stainless steel samples are fabricated by metal injection molding using water-atomized and gas-atomized powder with different oxygen contents. The influences of oxygen on the microstructural evolution and fatigue properties of the samples are investigated. The oxygen tends to react with Mn and Si to form oxide particles during sintering. The oxides hamper the densification process and result in decreased sintered density. Moreover, their existence reduces the Mn and Si dissolving into the base metal and compromises the solution strengthening effect. The oxides lead to stress concentration in the tensile and fatigue tests and become the initiation sites of fatigue cracks. After sintering, the samples made from the gas-atomized powder have a much lower oxygen content compared to those made from the water-atomized powder, therefore, exhibiting much better mechanical properties. The tensile strength, yield strength and the elongation of the samples made from the gas-atomized powder are 560 MPa, 205 MPa, and 58%, respectively. Their fatigue lives are about one order of magnitude longer than the samples made from water-atomized powder, and also longer than those fabricated by powder metallurgy and selective laser sintering which were reported in other studies.

Additive manufacturing of 316L stainless-steel structures using fused filament fabrication technology: mechanical and geometric properties

“…Finally, a comparison of the tensile performance of 3-D printed 316 L stainless steel samples manufactured with different techniques is presented in Table 1. It can be observed that Flat and On-edge sintered samples depicted similar tensile strength and stiffness values to those obtained by MIM process based on a similar sintering stage (Zhang et al, 2018;Agarwala et al, 1996;Yoon et al, 2003). In addition, 3-D printed SLS samples showed elongation to fracture values of 24%-42% for porosity levels between 1% and 2%, that are in accordance with the results obtained in this study (Suryawanshi et al, 2017;Kong et al, 2018;Li et al, 2019), and they are comparable, and even improving in certain cases, with published recent studied based on FFF technique (Gong et al, 2019;Damon et al, 2019).…”

“…The FFF technique generates a 3-D object through the deposition of a thermoplastic extruded filament. Furthermore, additive manufacturing of metals becomes increasingly important in many industrial fields (Gonzalez-Gutierrez et al, 2018;Zhang et al, 2018;Suryawanshi et al, 2017;Liverani et al, 2017;Kong et al, 2018). However, the current use of AM processes, such as laser-based powder bed fusion techniques, are quite complex and expensive to purchase and operate (Thompson et al, 2019;Gong et al, 2019;Damon et al, 2019;Gonzalez-Gutierrez et al, 2019).…”

“…Furthermore, 316 L austenitic stainless steel is a biocompatible material with good physical properties, such as high strength and corrosion resistance, making it ideal for biomedical applications. Many studies of additive manufacturing using selective laser sintering or melting processes of 316 L stainless steel have been conducted (Zhang et al, 2018;Suryawanshi et al, 2017;Liverani et al, 2017;Kong et al, 2018;Li et al, 2019;Tyagi et al, 2019). However, to date, there have been few studies on the fabrication and characterization of FFFbased 316 L austenitic stainless-steel parts post-processed with subsequent industry standard debinding and sintering stages (Gong et al, 2019;Damon et al, 2019).…”

Metal Powder Recyclability in Binder Jet Additive Manufacturing

“…During sintering, the residual oxygen content of SS 316L tends to react with alloying elements and form oxides in the sintered parts, and the presence of oxides may impede densification during sintering. 27 Powders with lower oxygen content have better sinterability and result in higher densification. 28 During sintering of 316L, oxides containing Mn and Si are more likely to be formed due to the lower DG (Gibbs free energy) of their oxidation reactions.…”

“…Moreover, the formation of SiO 2 and MnO reduces the amount of Si and Mn elements, which are essential contributors to the strengthening of the alloy, 29 thus leading to inferior tensile and ductility properties. 27 The formation of Si and Mn oxides during the LPBF process could enhance the mechanical properties 30 but may have detrimental effects on the densification of the sintered parts. Varying amounts of oxides may be present in the BJT parts, depending on the oxygen content.…”