Nucleation mechanism of the sigma-to-alpha phase transition in Fe_1-xCr_x

This Rapid Communication reports on Mossbauer-spectroscopy measurements of the kinetics of the sigma-to-alpha phase transition in the system Fe-Cr. By isothermally annealing samples of the compositions Fe53.8Cr46.2 and Fe51Cr49 at temperatures between 820 and 855 degrees C the authors gained information about the kinetics of the phase transition in terms of the Johnson-Mehl-Avrami-Kolmogorov equation. The obtained values for the Avrami exponent allow to draw conclusions about the type of nucleation mechanism. The behavior of the Avrami exponent for near-critical temperatures and for higher temperatures indicates a change in the nucleation mechanism with T-T-c.