Solid-State Diffusion Reaction and Formation of Intermetallic Phases in the Fe-Al System

The solid-state diffusion reaction between Fe and Al was studied using bulk diffusion couples in the temperature range 450°C to 600°C for annealing durations up to 240 h. The Al-rich intermetallic phase Fe₂Al₅ formed in the diffusion zone at all annealing temperatures. However, for diffusion couples annealed at and above 600°C, additional intermetallic phases Fe₃Al, FeAl, and FeAl₂ appeared in the diffusion zone. The existence of these phases at and below 640°C and the composition range of their existence were investigated, and these results provided better insight into the existing Fe-Al phase diagram. It was observed that Fe₂Al₅ is the dominant phase in the diffusion zone, and the formation of this phase was rationalized based on the modified effective heat of formation model. Both kinetic and diffusion parameters were evaluated for Fe₂Al₅, and the activation energy for interdiffusion of this phase was found to be 146.8 kJ/mol; these results were compared with previously published work.