Mechanical spectroscopy of the Zener relaxation in Fe-22Al and Fe-26Al alloys

Two Fe-Al alloys with ∼22 and 26 at% Al have been studied using iso-and athermal mechanical spectroscopy. The Zener relaxation caused by reorientation of pairs of Al atoms in Fe is used to evaluate the activation parameters of Al atom jumps in Fe. Isothermal mechanical spectroscopy (frequency variations from 10−4 to 102 Hz) gives some advantages as compared with ordinary technique, i.e. study of anelasticity as a function of temperature. The advantage is an opportunity to avoid different transient effects and to measure materials in a state close to equilibrium. This allows to distinguish clearly between Al atom diffusion in A2, B2 and D03 states. The Arrhenius plot for Zener relaxation in the Fe-22 and Fe-26%Al alloys exhibits activation energies: for Fe-22Al in the disordered A2 range the HA2≈238 kJ/mol and in the D03 (+A2) ordered range the HD03≈270 kJ/mol; for Fe-26Al in the B2 range the HB2≈235 kJ/mol, and in the D03 ordered range the HD03≈286 kJ/mol. The structural state of the alloys was characterised by TEM and heat flow (DSC) studies.