On the phase transformation pathway during localized grain boundary oxidation in an Fe-10 at% Cr alloy at 200?C

We have performed short-term, controlled oxidation experiments of sputter deposited Fe-10 at% Cr alloy films at 200 degrees C. Nanoscale structural characterization by four-dimensional scanning transmission electron microscopy (4d-STEM) and chemical characterization by atom probe tomography (APT) have provided insights on the phase transformation pathway followed during localized, inward-progressing oxidation of grain boundaries at this low temperature. Direct nucleation of a metastable spinel-structured oxide, with suppression of the corundum -structured Cr2O3 has been observed even at the early stages. A `partitioning-free oxide nucleation mechanism' under conditions of extremely restricted kinetics is proposed to explain the non-equilibrium transformation pathway.