Development of chromium nitride layers on Inconel 625: impact on structural integrity and chemical stability

Abstract This study evaluated the surface modification of Inconel 625 superalloy by conventional plasma nitriding (PN) and cathode cage plasma nitriding (CCPN), performed at 450 °C and 500 °C for 5 h. The samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness testing under 50 gf for 15 s, roughness measurements, adhesion testing under 150 kgf, potentiodynamic polarization in 3.5 wt% NaCl solution, and pin-on-disc wear testing against an AISI 52,100 steel ball under 5 N for 3000 s. The results confirmed the formation of the CrN phase under all treatment conditions. Surface hardness increased after nitriding, with the CC500 condition reaching 1573.57 HV, corresponding to a 383.7% increase compared with the untreated alloy. Adhesion tests indicated satisfactory performance, especially for the CC450 condition, which was classified as HF1. From an electrochemical standpoint, the treatments shifted the surface behavior toward more noble potentials, with PN450 showing the lowest corrosion current density of 3.71 × 10 − 9 mA cm − 2 . Tribological performance was also improved, as the nitrided samples showed reduced disk wear and promoted the formation of protective Fe- and O-rich tribofilms during sliding. Therefore, PN and CCPN show high potential for naval components, representing efficient and sustainable alternatives to improve the durability of Inconel 625 in marine environments.