Achieving Inconel 625-comparable high-temperature corrosion resistance by laser-cladded Al/FeCrAl composite coatings for waste-to-energy applications

High-temperature corrosion behavior of laser-cladded Al/FeCrAl composite coatings in a simulated waste-to-energy (WTE) incineration environment was systematically investigated. The coatings were designed by introducing an Al interlayer beneath a Fe-13Cr-7Al top layer to improve Al availability while maintaining coating integrity. Results showed that the Al interlayer thickness strongly affected coating microstructure, hardness, and corrosion resistance. Increasing the Al interlayer thickness promoted the formation of FeAl intermetallics and Al₂O₃, and significantly enhanced coating hardness. However, excessive Al addition caused coating delamination or through-thickness cracking because of the formation of brittle FeAl phases and increased thermal stress during solidification. Among all samples, the 7Al-3 coating exhibited the best overall performance, showing a dense and crack-free microstructure and a mass loss of 1989 g·m⁻² after 168 h at 650 °C, which was comparable to that of laser-cladded Inconel 625 (1925 g·m⁻²) and markedly lower than that of 12Cr1MoV steel (4082 g·m⁻²). This superior performance was mainly attributed to the outward diffusion of Al from the composite coating, which promoted the continuous formation of protective Al-rich oxide scales and suppressed the consumption of Fe and Cr. Cracks and grain boundaries acted as the main corrosion pathways, whereas Al enrichment at these regions effectively retarded further corrosion propagation. Therefore, the Al/FeCrAl composite coating strategy can effectively overcome the cracking tendency associated with high Al content in single-layer FeCrAl coatings, while achieving a 168 h mass loss comparable to that of laser-cladded Inconel 625 under the present test conditions, showing strong potential for waste incineration superheater protection.