Surface engineering strategies for Ni-Cr and Cr₃C₂-NiCr Coatings: A systematic review of thermal spray processing, post-treatment, and high-temperature degradation resistance

Nickel-chromium (Ni-Cr) and chromium carbide–nickel chromium (Cr₃C₂-NiCr) coatings are widely used to protect industrial components exposed to high-temperature oxidation, erosion, corrosion, hot corrosion, and tribological wear. However, coating performance remains difficult to generalize because it is strongly affected by deposition route, feedstock characteristics, post-treatment, microstructure, substrate, and service environment. This systematic review synthesizes and critically evaluates 106 studies published between 2016 and 2026 to establish quantitative process–performance relationships and develop an evidence-informed framework for service-specific selection of Ni–Cr and Cr₃C₂–NiCr coating systems. The quantitative synthesis demonstrates that high-velocity deposition routes, particularly high-velocity oxygen-fuel (HVOF) and high-velocity air-fuel (HVAF) spraying, consistently produce dense, low-porosity coatings with superior adhesion, hardness, and wear or erosion resistance. However, coating performance is ultimately governed by the combined effects of particle thermal–kinetic history, carbide retention, splat cohesion, porosity evolution, and service-specific operating conditions rather than by deposition technology alone. Other methods, including cold spray, plasma spray, arc spray, laser cladding, and electrical discharge coating, offer complementary advantages for specific substrates and service conditions. Corrosion and oxidation resistance are mainly governed by protective oxide formation, binder continuity, intersplat bonding, porosity, residual stress, and the ability to restrict inward diffusion of molten salts, chlorides, sulfates, and oxidizing species. Post-processing methods such as ultrasonic nanocrystal surface modification, surface mechanical attrition treatment, heat treatment, and laser remelting further enhance performance by reducing surface defects and refining microstructure. Overall, no single deposition process or coating composition is universally optimal. Instead, this review integrates quantitative evidence into an evidence-informed process–microstructure–degradation framework that supports service-specific coating selection and identifies the key microstructural factors governing long-term performance under severe wear, corrosion, erosion, and high-temperature oxidation environments.