Improving the wear and corrosion resistance of new generation cast i̇rons (SSFF) wi̇th hvof thermal spray coati̇ng method

In this thesis, it is aimed to develop a wear and corrosion resistant, high hardness surface on solid solution strengthened ferritic ductile cast iron (SSF) by using HVOF (High Velocity Oxy Fuel Spraying) thermal spray coating method which offers better surface properties compared to conventional coating methods. Solid solution strengthened ferritic ductile cast iron (SSF) is a new (second) generation of cast iron and is considered as an alternative to forged and cast steels. Although they have advantages such as relatively low cost, low melting point, light weight, fluidity, castability, machinability and homogeneous mechanical properties throughout the part, they have relatively poor wear, corrosion and fatigue resistance under harsh conditions. At this point, it is necessary to develop parts with high surface quality. In this context, wear and corrosion resistant, high hardness surfaces are developed by using HVOF thermal spray coating method which offers high quality surface properties. In the proposed study, it is aimed to develop parts with high surface hardness, high wear and corrosion resistance by coating WC-Co and WC-Co(Cr) with HVOF method on new generation cast irons with EN-GJS-600-10 standard. WC-Co and WC-Co(Cr) coatings applied to SSF cast irons using the HVOF thermal spray coating method have provided significant performance improvements compared to the base material. A noticeable increase in hardness has been observed; the WC-Co coating achieved a hardness value of 1176 HV, while the WC-Co(Cr) coating reached 1248 HV, providing approximately six times the hardness of the base material (~199 HV). In terms of wear resistance, while a wear mark 200 μm deep formed on the uncoated sample, only superficial scratches were detected on the coated samples, and SEM-EDS analyses confirmed that the substrate material (Fe) was not reached in the wear areas. The WC-Co coating stood out particularly in terms of corrosion resistance. With an open-circuit potential (OCP) of -0,230 V, it exhibited more noble behavior compared to the substrate (-0,481 V), and PDP and EIS analyses also demonstrated superior protection by showing low corrosion current density and high charge transfer resistance. Adhesion strength was clearly evident in scratch tests; the WC-Co(Cr) coating reached a critical load value of 30,1 N, demonstrating the positive effect of Cr addition on fracture resistance. In conclusion, both HVOF coatings comprehensively improved the surface performance of SSF cast iron in terms of hardness, wear resistance, and corrosion resistance.