Phase separation kinetics in a Fe–Cr–Al alloy

The α–α′ phase separation kinetics in a commercial Fe–20 wt.% Cr–6 wt.% Al oxide dispersion-strengthened PM 2000™ steel have been characterized with the complementary techniques atom probe tomography and thermoelectric power measurements during isothermal aging at 673, 708, and 748 K for times up to 3600 h. A progressive decrease in the Al content of the Cr-rich α′ phase was observed at 708 and 748 K with increasing time, but no partitioning was observed at 673 K. The variation in the volume fraction of the α′ phase well inside the coarsening regime, along with the Avrami exponent 1.2 and activation energy 264 kJ mol−1, obtained after fitting the experimental results to an Austin–Rickett type equation, indicates that phase separation in PM 2000™ is a transient coarsening process with overlapping nucleation, growth, and coarsening stages.