Fe2Al5

Fe2Al5 is an intermetallic compound in the binary iron–aluminum system, with the stoichiometry Fe2Al5. It represents a distinct phase that appears in the Fe–Al phase diagram within certain composition and temperature ranges and is typically observed in Al-rich alloys after appropriate heat treatment. The phase is identified in phase-equilibrium studies and can coexist with other aluminides depending on processing conditions.

Crystal structure and characterization: The crystal structure of Fe2Al5 is described as complex, common among aluminides, and not easily classified by simple close-packed motifs. It forms a relatively large unit cell that contains both iron-containing motifs and aluminum-rich segments. Its presence is usually confirmed by diffraction techniques and electron microscopy, which reveal characteristic ordering of Fe and Al on specific lattice sites.

Properties: Fe2Al5 is generally regarded as brittle and not ductile at ambient conditions, a typical trait of many intermetallic compounds. It tends to exhibit high hardness and chemical stability relative to pure metals, along with limited solubility with neighboring phases in the Fe–Al system. These properties contribute to its limited use as a structural material.

Formation and synthesis: Fe2Al5 can be produced by high-temperature diffusion or direct reaction between iron and aluminum, and by heat treatment of Fe–Al alloys with sufficient Al content. Its formation is highly sensitive to temperature, overall composition, and cooling history, and it often arises during phase transformations within the Al-rich portion of the Fe–Al diagram.

Applications and significance: The phase is primarily of interest for phase-equilibria studies, diffusion research, and fundamental understanding of the Fe–Al system. Due to brittleness and processing challenges, Fe2Al5 has no widespread commercial application as a structural material.