**1. Introduction**

Inconel 718 is a super-alloy. Due to its excellent high-temperature performance, it is widely used in aircraft turbojet engines as discs, blades, and casing for high-pressure sections of aircraft engine components. It also finds application in rocket engines and cryogenic environments due to its good toughness at low temperatures, which protects the components from brittle fracture. Due to excellent mechanical properties and wear resistance, the Inconel 718 is favorable for aerospace, marine and chemical industries. However, the higher shear strength and low material removal rate of Inconel 718 create difficulty in machining, especially for complex parts where tight dimensional accuracy is required [1–3]. Additive manufacturing (AM) provides an excellent opportunity to overcome the difficulty of conventional machining to develop a complex structure of Inconel 718 [4,5].

Among the different methods of AM techniques, laser powder bed fusion (LPBF) has gained tremendous attention due to its capability to fabricate a fully dense component [6,7]. LPBF is also referred as direct laser sintering or selective laser melting. LPBF technique involves layer-by-layer formation where a layer of powder is applied to the

**Citation:** Siddaiah, A.; Kasar, A.; Kumar, P.; Akram, J.; Misra, M.; Menezes, P.L. Tribocorrosion Behavior of Inconel 718 Fabricated by Laser Powder Bed Fusion-Based Additive Manufacturing. *Coatings* **2021**, *11*, 195. https://doi.org/ 10.3390/coatings11020195

Academic Editor: Kevin Plucknett Received: 21 December 2020 Accepted: 5 February 2021 Published: 8 February 2021

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platform/substrate and subsequently melted using laser. The melting of the powders causes bonding between powders and forms the first layer. Similarly, successive layers of powders are formed to fabricate the coating/parts. LPBF technique has been used to fabricate different standalone coatings (ref.) and 3D components (ref.) of various materials such as Ti6Al4V coating [8], tantalum coating [9], Ti-SiC coating [10], 316L stainless steel [11], and Inconel 718 [12] etc.

LPBF has enabled customization of Inconel 718 components with easy production of complex shapes and geometries. During its operation, especially in aircraft and jet applications, the material may come in contact with various extreme and aqueous environments in addition to tribo-contacts with other materials [13]. These conditions can cause early failure or reduced performance of AM Inconel 718 components if the AM design or fabrication process has any flaws. It is also well known that the Inconel 718 provides excellent corrosion resistance. It has been shown that the AM Inconel 718 can maintain pitting corrosion resistance even after low-temperature solution treatments, while high-temperature solution treatments can cause some weakening of the pitting corrosion resistance [13–15]. Additionally, the electrochemical polishing process can significantly improve pitting corrosion resistance. Build direction using LPBF has also shown a significant influence on microstructure and corrosion performance of Inconel 718. The corrosion resistance of the AM Inconel 718 samples increases with the increasing incline angle of LPBF process, and this can be rationalized by considering changes to the grain boundary area [16]. To make the AM Inconel 718 tribo-contact interfaces functionally resistant in extreme environmental conditions, it is necessary to investigate the wear along with the electrochemical behavior of these alloys. Hence, understanding the tribological and tribocorrosion behavior of functionally processed Inconel 718 materials are of practical and theoretical importance.
