Diffusion couple experiments and calculations in Fe-Cr-Ni-Al system at 800–1000 °C

Abstract

The phase equilibria in the Fe-Cr-Ni-Al system was investigated between 800 and 1000 °C with diffusion couple technique. The experiments were carried out at 800, 900, 950, and 1000 °C using the single-phase terminal alloys (in wt%) Fe-25Cr-5Al (BCC, α) and Fe-30Ni (FCC, γ). The experiments showed the formation of β-NiAl phase in the diffusion couples annealed between 800 and 950 °C. No new phase was formed in the diffusion couple annealed at 1000 °C. New experimental data concerning α + β tie-line and α + β + γ tie-triangle at 800–950 °C, and the α + γ tie-line data at 1000 °C were obtained using EPMA measurements. The results were compared with thermokinetic calculations using two different combinations of commercial thermodynamic and mobility databases. The calculation performed using the database combination for nickel-base alloys predict the formation of the β phase at 800 and 900 °C, but not at 950 °C. The width of the α + β field in the calculated diffusion profile, however, differed considerably from the measured profile. The database combination for ferrous alloys did not predict the formation of the β phase at any of the temperatures.