Wear and corrosion behavior of titanium carbide coatings grown on the surface of ductile iron

The fact that ductile iron can be produced more economically than steel with relatively lower density and the well-known characteristics of cast iron such as high castability, vibration dampening, and load-bearing capability make this alloy group a desirable alternative to steels in numerous applications in the industry. But unfortunately, the low surface hardness and average corrosion resistance of ductile iron restrict its applications, especially in tribo-corrosive applications where wear and corrosion resistance is simultaneously required. The initiation sites for corrosion and wear are the surface, therefore the improvement of surface properties will directly influence the resistance to corrosion and wear. In this study, titanium carbide (TiC) coatings were grown on the surfaces of ductile iron (GGG-80) grade samples by thermo-reactive diffusion (TRD) at temperatures of 800 °C, 850 °C and 900 °C for 4 h. The resulting TiC coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), surface profilometry, microhardness tests, VDI adhesion tests, wear tests, and electrochemical corrosion tests. Depending on the TRD temperature, smooth, continuous, and crack-free TiC coatings with 5–11 µm and 27.96–32.45 GPa average hardness were obtained on the surface. The coating also exhibited good adhesion with the substrate. The high chemical stability, hardness, and good adhesion strength of the TiC coatings also provided low friction high wear resistance, and superior corrosion resistance compared to the untreated ductile iron. While delamination and oxidation-assisted abrasive wear were observed in the untreated sample, only oxidation-assisted adhesive wear was observed in the TiC coated samples. Selective corrosion due to galvanic effects was observed in the untreated sample, whereas a more homogeneous form of corrosion combined with pitting was observed in the TiC coatings. The improvement in the wear and corrosion resistance displayed by the presence of the TiC coatings showed that TiC coatings produced by thermo-reactive diffusion can be used for increasing the service life of ductile irons considered for tribo-corrosion applications.