Wear and corrosion resistance of niobium-chromium carbide coatings on AISI D2 produced through TRD

Niobium carbide, chromium carbide and niobium-chromium carbide coatings were deposited using the thermo-reactive diffusion (TRD) deposition technique on AISI D2 steel substrates, and their wear and corrosion resistance was studied. The morphology of the coatings was characterized through optical and scanning electron microscopy (SEM), and the crystalline structure was studied through X-ray diffraction (XRD). Chemical composition was evaluated via energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The hardness of the coatings was measured through nanoindentation, and their wear was studied using the ball on disk test. The electrochemical behavior was assessed with potentiodynamic polarization and electrochemical impedance (EIS) tests. The XRD results show the formation of the NbC for the niobium carbide coating, Cr23C6 and Cr7C3 for the chromium carbide coating, and NbC, Cr23C6 and Cr7C3 for the niobium-chromium coating. Hardness value for the niobium-chromium carbide coating was 27.62 ± 2.56 GPa, which was higher in comparison to 21.66 ± 0.5 GPa for niobium carbide, 14.7 ± 1.1 GPa for chromium carbide and 6.70 ± 0.28 GPa for the uncoated steel. The wear resistance obtained was higher for the niobium-chromium carbide coating. However, its corrosion resistance was lower than the corrosion resistance for binary coatings.