Reactively sputtered coatings for the protection of a nickel-based alloy against heavy oil corrosion fouling

Critical components in the petrochemical industry require materials resistant to wear, corrosion, and fouling to withstand hydrocracking conditions. This work evaluates the fouling resistance of nitride coatings, sputter-deposited on Inconel 718 substrates by RF and pulsed DC magnetron sputtering, followed by processing heavy oil at high temperature (450 °C) and high pressure (>11 MPa). The nitride coatings protected the surface against diffusion, oxidation, and sulfidation. Specifically, the amorphous nitride film (am-Coating) exhibited better anticoking properties, while the polycrystalline nitrides (pc-Coating) offered superior mechanical performance. Contact angle measurements indicated that the pc-Coating was hydrophobic, with a surface energy dispersive component 41% higher than the am-Coating, potentially increasing its affinity for organic fouling and consequently poorer anticoking performance. The am-Coating exhibited a hardness of 17.5 GPa, with a cohesive failure (LC1) at 3.99 N and an adhesive failure (LC2) at 7.28 N. Incorporating a silicon (Si) interlayer improved LC1 and LC2 to 4.94 and 8.27 N, respectively, without significantly altering the hardness. The pc-Coating demonstrated a higher hardness of 27.0 GPa, with LC1 at 6.12 N, and no adhesive failure observed up to 20 N. The mechanical properties may have also contributed to the difference in foulant adhesion between the amorphous and polycrystalline coatings. Boriding of the Inconel 718 alloy was explored as an alternative to create a gradient of elasto-plastic properties from the substrate bulk toward the coating surface. However, standard borided samples performed poorly against fouling before and after the nitride depositions.