Surface modification and tribological behavior of plasma nitrided Inconel 718 manufactured via direct melting laser sintering method

Abstract

Currently employed in aerospace, defense, oil, and gas applications, Inconel 718 (IN718) is an indispensable alloy with excellent thermo-mechanical properties and hot corrosion resistance. Inconel (IN718) has become the gold standard to manufacture turbine blades, bearing housing parts, compressor seals, drive couple gears, side pocket mandrels, wellheads, packers, and safety valves. Additive Manufacturing (AM) or 3D printing technology is a promising alternative to fabricate and repair nickel-based superalloy components, characterized by challenging processing through conventional methods due to the mechanical strength of the alloys or the geometric complexity of the piece. Furthermore, many applications require surface protection features, such as high hardness, corrosion, and wear resistance. These properties can be achieved by applying hard coatings and/or surface thermochemical treatments such as plasma nitriding. This study reports the effect of plasma nitriding applied on Laser Powder Bed Fusion (LPBF) additively manufactured IN718. Depending on the time, the treatment produced a 1.5–2.8 μm nitrided protective bi-layer composed by an outer CrN containing layer followed by an inner austenitic expanded γN layer. The growing kinetics analysis shows that the nitriding process follows a parabolic behavior. The nitriding process also increases the surface roughness as a result of case hardening formation reaching ~ 60 nm within 2 h. No measurable wear on the plasma nitrided additively manufactured IN718 alloy was recorded.