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

Abstract

A direct energy deposition (DED) process using wires is considered an additive manufacturing technology that can produce large components at an affordable cost. However, the high deposition rate of the DED process is usually accompanied by poor surface quality and inherent printing defects. These imperfections can have a detrimental effect on fatigue endurance and corrosion fatigue resistance. The aim of this study was to evaluate the critical effect of phase transition and printing defects on the corrosion fatigue behavior of 316L stainless steel produced by a wire laser additive manufacturing (WLAM) process. For comparison, a standard AISI 316L stainless steel with a regular austenitic microstructure was studied as a counterpart alloy. The structural assessment of printing defects was performed using a three-dimensional non-destructive method in the form of X-ray microtomography (CT) analysis. The microstructure was evaluated by optical and scanning electron microscopy, while general electrochemical characteristics and corrosion performance were assessed by cyclic potentiodynamic polarization (CCP) analysis and immersion tests. The fatigue endurance in air and in a simulated corrosive environment was examined using a rotating fatigue setup. The obtained results clearly demonstrate the inferior corrosion fatigue endurance of the 316L alloy produced by the WLAM process compared to its AISI counterpart alloy. This was mainly related to the drawbacks of WLAM alloys in terms of having a duplex microstructure (austenitic matrix and secondary delta-ferrite phase), reduced passivity, and a significantly increased amount of intralayer porosity that acts as a stress intensifier of fatigue cracking.

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 ]).…”

Effects of Solid-Solution Carbon and Eutectic Carbides in AISI 316L Steel-Based Tungsten Carbide Composites on Plasma Carburizing and Nitriding

“…Steel materials, particularly austenitic stainless steels such as AISI 316L, which are readily available and exhibit excellent corrosion resistance, are actively used for additive manufacturing. The metallurgical and mechanical properties of additively manufactured AISI 316L stainless steels have been extensively studied [7][8][9][10][11][12][13]. Additive manufacturing via laser metal deposition has been used to improve the wear resistance of stainless-steel materials via compositing with tungsten carbide particles [14][15][16][17][18].…”

Effect of Microstructure Modifications on Stress Corrosion Endurance of 15-5 PH Stainless Steel Formed by Wire Laser Additive Manufacturing (WLAM)

“…Both WAAM and WLAM enable a deposition rate of up to 3 kg/h, compared to 0.1 kg/h for PBF, as well as the production of large components with near-net-shape structures. In addition, it should be pointed out that WAAM and WLAM technologies allow the use of a wide range of metals and alloys to produce a variety of components for different industries [18][19][20]. The main disadvantage of those technologies compared to PBF is the relatively rough resultant surface that usually requires additional machining processes [21,22].…”