Microstructure, Tribological, and Corrosion Behaviour of HVOF-Sprayed (Cr₃C₂-NiCr+Ni) Coatings on Ductile Cast Iron

The HVOF (High Velocity Oxy-Fuel) thermal spraying method is widely used in surface engineering to produce coatings with high hardness, low porosity and high crack resistance. Composite coatings with particles of chromium carbide (Cr₃C₂) in a nickel-chromium alloy (NiCr) matrix are used in demanding operating conditions, such as the energy and transport sectors. The study aims to compare the microstructure, micro-mechanical and tribological properties and corrosion resistance of two types of coatings: Cr₃C₂-25(Ni20Cr)-10(Ni) and Cr₃C₂-25(Ni20Cr), deposited by the HVOF method on a ductile cast iron substrate. Particular attention is paid to the influence of nickel (Ni) particles on the microstructure, mechanical properties, wear resistance and corrosion in the context of improving the service life of coatings. The study included microstructure analysis using light microscopy (LM) and scanning electron microscopy (SEM), as well as chemical and phase composition analysis in micro-areas using EDS and XRD techniques. The results show that the Cr₃C₂-25(Ni20Cr) coating enriched with Ni particles was characterised by a compact structure with low porosity and high hardness. Its microstructure consists of large, partially melted Ni particles and fine carbide particles (Cr₃C₂ and Cr₇C₃) embedded in the NiCr matrix, some of which reach submicron sizes. Performance tests, including indentation tests (HIT, EIT, KIC) as well as scratch and corrosion resistance tests, confirmed that the presence of Ni particles increases the coating's resistance to cracking, wear and corrosion. As a result, these coatings are characterised by higher operational durability, making them more effective in difficult working conditions.