Microstructure, Tribological, and Corrosion Behavior 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 excellent crack resistance. Composite coatings with chromium carbide (Cr₃C₂) in a nickel-chromium (NiCr) matrix are commonly applied in demanding environments, such as the energy and transport sectors. This study compares the microstructure, mechanical, tribological, and corrosion properties of two coatings-Cr₃C₂-25(Ni20Cr)-10(Ni) and Cr₃C₂-25(Ni20Cr)-deposited on ductile cast iron using HVOF. The addition of 10 wt.% Ni enhances coating integrity, mechanical performance, and environmental resistance by improving ductility, reducing residual stress, enhancing wettability, and balancing hardness with improved crack, wear, and corrosion resistance. Microstructure analysis via LM (Light Microscopy) and SEM (Scanning Electron Microscopy), along with chemical and phase characterization using EDS (Energy Dispersive X-ray Spectroscopy) and XRD (X-ray Diffraction), revealed that the Ni-enriched Cr₃C₂-25(Ni20Cr)-10(Ni) coating exhibited a denser structure, lower porosity, and high hardness. Its microstructure consists of large, partially melted Ni particles and fine Cr₃C₂ and Cr₇C₃ carbides embedded in the NiCr matrix, some at submicron scales. Performance tests, including indentation (H_IT, E_IT, K_IC), scratch, and corrosion resistance assessments, confirmed that Ni addition improves crack resistance, wear durability, and corrosion protection. Consequently, these coatings demonstrate superior operational durability, making them more effective in challenging environments.