The Effect of a Slow Strain Rate on the Stress Corrosion Resistance of Austenitic Stainless Steel Produced by the Wire Laser Additive Manufacturing Process

Abstract

The wire laser additive manufacturing (WLAM) process is considered a direct-energy deposition method that aims at addressing the need to produce large components having relatively simple geometrics at an affordable cost. This additive manufacturing (AM) process uses wires as raw materials instead of powders and is capable of reaching a deposition rate of up to 3 kg/h, compared with only 0.1 kg/h with common powder bed fusion (PBF) processes. Despite the attractiveness of the WLAM process, there has been only limited research on this technique. In particular, the stress corrosion properties of components produced by this technology have not been the subject of much study. The current study aims at evaluating the effect of a slow strain rate on the stress corrosion resistance of 316L stainless steel produced by the WLAM process in comparison with its counterpart: AISI 316L alloy. Microstructure examination was carried out using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction analysis, while the mechanical properties were evaluated using tensile strength and hardness measurements. The general corrosion resistance was examined by potentiodynamic polarization and impedance spectroscopy analysis, while the stress corrosion performance was assessed by slow strain rate testing (SSRT) in a 3.5% NaCl solution at ambient temperature. The attained results highlight the inferior mechanical properties, corrosion resistance and stress corrosion performance, especially at a slow strain rate, of the WLAM samples compared with the regular AISI 316L alloy. The differences between the WLAM alloy and AISI 316L alloy were mainly attributed to their dissimilarities in terms of phase compositions, structural morphology and inherent defects.

The Influence of Intralayer Porosity and Phase Transition on Corrosion Fatigue of Additively Manufactured 316L Stainless Steel Obtained by Direct Energy Deposition Process

“…Further analysis on the XY plane (printing path-top cross-section view) revealed the existence of a duplex microstructure composed of an austenitic matrix and a secondary ferritic phase [ 13 ], as expected from the Schaeffler diagram [ 40 ] and introduced in Figure 4 . This microstructure of WLAM 316L alloy is in contrast to the pure austenitic morphology of its counterpart AISI 316L alloy, which has the same chemical composition [ 6 , 40 ]. In terms of printing defects, Figure 5 clearly demonstrates the presence of macroporosity and microporosity with sizes of 1 µm and up to 6 µm, respectively, in both the XY and XZ planes.…”

“…For example, the pitting density in WLAM 316L was 14-times higher than that obtained by the counterpart AISI 316L alloy. This could be mainly related to the inherent process defects of the WLAM 316L alloy and the fact that this alloy contains a ferritic phase with reduced corrosion resistance [ 6 , 11 ].…”

“…Additive manufacturing (AM) technologies are primarily developed to rapidly produce complex geometries without the need for additional machining and post-processing procedures [ 1 , 2 ]. This has been commonly achieved using powder bed fusion (PBF) technologies such as selective laser melting (SLM) and electron beam melting (EBM) [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. However, the main limitation of PBF technologies relates to their inability to produce large parts at an affordable cost [ 15 , 16 ].…”

“…They distinguished between interlayer porosity and intralayer porosity. While interlayer porosity is related to insufficient heating, which creates an un-melted region and is also known as lack of fusion [ 6 ], intralayer porosity is connected to the use of an inert shielding gas that promotes gas entrapment. Usually, intralayer porosity will have a spherical shape and tends to evolve at arbitrary sites with a relatively reduced solidification rate.…”

Additive Manufacturing Technologies of High Entropy Alloys (HEA): Review and Prospects

“…Research studies on the AM of HEAs can be broadly classified into four main process technologies: (i) PBF, in which a powder is spread on a printing tray and selectively melted by an energy source, such as a laser beam [ 23 , 24 , 25 , 26 ], an electron beam [ 27 ], or arc melting [ 28 ]; (ii) DED, in which the metal raw material is directly melted layer by layer using different energy sources, such as a laser beam, an electron beam, or arc melting, and the feedstock material can be in the form of powder (using blown powder deposition (BPD) technology [ 29 , 30 ]) or in the form of wire (using arc and laser melting as the heat source—that are usually known as wire arc AM (WAAM) [ 31 , 32 , 33 , 34 ] and wire laser AM (WLAM) [ 35 , 36 ]); (iii) BJ, where the powder bed technology uses a liquid binder instead of a heat source, and consequently the printed part is in the form of a green body that requires sintering to obtain adequate density [ 37 , 38 ]; and (iv) ME, where the mixture of powder and binder is extruded through a nozzle to fabricate layer by layer (in this case the printed part is also a green body that requires sintering [ 39 , 40 ]).…”