Mossbauer study of the spinodal decomposition in a Fe-Cr-Co alloy

Spinodal decomposition which occurs at a temperature higher than 475 degrees C in Fe-Cr-Co alloys (chromindur), plays a prominent part in the embrittlement phenomenon and strongly influences the magnetic properties. In the present study, the spinodal decomposition in the Fe-31Cr-12Co alloy has been investigated using Fe-57 Mossbauer effect as a function of aging time at a temperature of 520 degrees C. An addition of Cobalt causes a transition of the aging behaviour from the nucleation and growth to the spinodal decomposition and rises its decomposition temperature. Mossbauer spectra for the as-quenched alloy, takes at 300 K, show a typical magnetic sextet with broad lines: the hyperfine structure can be reproduced by using a distribution of hyperfine fields consistent with the presence of various kinds of iron environments. The aging at 520 degrees C, reveals the presence of three main environments: a Co-rich Fe phase with high concentration of Co, a Fe phase and a (Fe, Cr) phase with high concentration of Cr.