Phase separation in PM 2000™ Fe-base ODS alloy: Experimental study at the atomic level

The coarsening of the three-dimensional microstructure resulting from phase separation during ageing at 748 K of a Fe-based PM 2000™ oxide dispersion strengthened (ODS) steel has been investigated by atom probe tomography and hardness measurements. Phase separation resulted in the formation of isolated particles of the chromium-enriched α′ phase. The aluminum and titanium were found to preferential partition to the iron-rich α phase. The partitioning of aluminum is consistent with theoretical calculations. The change in the scale of the chromium-enriched α′ phase was found to fit a power law with a time exponent of 0.32 in accordance with that predicted by the classical Lifshitz, Slyozov and Wagner (LSW) theory. The solute concentrations of the coexisting α and α′ phases were estimated from concentration frequency distributions with the Langer-Bar-on-Miller (LBM) method and proximity histograms. The hardness was linearly related to the chromium content of the α′ phase.