Internal Friction of Austenitic Fe-Mn-C-Al Alloys

The internal friction (IF) spectra of Fe-Mn-C-Al alloys with a face-centered-cubic (fcc) austenitic phase were measured at a wide range of temperature and frequency (f) to understand the mechanisms of anelastic relaxations occurring particularly in Fe-Mn-C twinning-induced plasticity steels. Four IF peaks were observed at ~346 K (73 °C) (P₁), 389 K (116 °C) (P₂), 511 K (238 °C) (P₃), and 634 K (361 °C) (P₄) when f was 0.1 Hz. However, when f increased to 100 Hz, whereas P₁, P₂, and P₄ disappeared, only P₃ remained without the change in peak height, but with the increased peak temperature. P₃ matches well with the IF peak of Fe-high Mn-C alloys reported in the literature. The effects of chemical composition and vacancy (v) on the four IF peaks were also investigated using various alloys with different concentrations of C, Mn, Al, and vacancy. As a result, the defect pair responsible for each IF peak was found as follows: a v-v pair for P₁, a C-v pair for P₂, a C-C pair for P₃, and a C-C-v complex (major effect) + a Mn-C pair (minor effect) for P₄. These results showed that the IF peaks of Fe-Mn-C-Al alloys reported previously were caused by the reorientation of C in C-C pairs, not by the reorientation of C in Mn-C pairs.