Fe/Al and Ni/Al coatings – composition and intermetallic formation

The demand for durable, oxidation-resistant coatings for high-temperature tooling requires an understanding of intermetallic phase formation and thermal stability. Intermetallic coatings are being explored more for use in high-temperature and chemically aggressive applications. The effect of thermal treatment on Fe/Al and Ni/Al coatings deposited by thermal spraying on grey cast iron substrates was investigated with emphasis on composition, microstructure and intermetallic phase formation. Annealing experiments at different temperatures provided insight into solid state diffusion processes. During annealing, interdiffusion between the coating and substrate components led to the formation of homogeneous intermetallic phases on the surface. The results showed that both chemical composition and annealing parameters influence the hardness of thermally sprayed coatings. Temperature and duration were found to have a significant effect on intermetallic phase formation. For Fe/Al coatings, annealing at 700°C resulted in the formation of FeAl and Fe ₃ Al intermetallic compounds, whereas at 1000°C only the FeAl phase remained. In Ni/Al coatings, annealing at 700°C resulted in the formation of multiple phases, including Ni ₃ Al, NiAl, and Ni ₂ Al ₃ , while at 1000°C only the NiAl phase was present. Optimization of thermal treatment processes can significantly improve the mechanical and chemical properties of coatings, making them suitable for a wide range of applications in industries.