aluminide

An aluminide is a compound formed between aluminum and a more electropositive metal, typically an intermetallic with a fixed stoichiometry. Common aluminides include Ni3Al, NiAl, TiAl, FeAl, and CoAl. They are characterized by ordered crystal structures and limited solubility with other elements.

Aluminides often exhibit high melting points and high-temperature strength, along with good oxidation resistance due to the formation of protective alumina scales on exposed surfaces. However, many aluminides are relatively brittle at room temperature and may show limited ductility, which can complicate processing and design.

Many aluminides are used or considered for high-temperature structural applications. Intermetallics such as gamma-TiAl or beta-NiAl are being explored for lightweight turbine components and aerospace structures because of their favorable strength-to-weight ratios and oxidation resistance. NiAl and FeAl, in particular, have been studied for use in coatings and as bond coats or structural materials in certain thermal environments.

Processing methods include diffusion reactions to form aluminide layers on another metal (diffusion aluminides), pack cementation, chemical vapor deposition, and other surface engineering approaches. These coatings, often called aluminide coatings, enhance oxidation and corrosion resistance by promoting the growth of a protective Al2O3 scale during service.

Limitations and ongoing research address improving ductility, fracture toughness, and high-temperature stability of aluminides, as well as overcoming brittleness and aging effects in service.