Anelasticity of iron-aluminide Fe3Al type single and polycrystals

Abstract

Mechanical spectroscopy and in situ neutron diffraction techniques were employed to study and interpret anelasticity in Fe-27 at.%Al single crystal (SC) and polycrystal (PC) alloys from room temperature to 600 °C. Thermally activated Zener relaxation was recorded in the temperature dependent internal friction (IF) curves for both SC and PC alloys upon heating and cooling. The reversible second-order D03 ↔ B2 phase transition studied by in situ neutron diffraction leads to a transient anelastic effect at ∼550 °C both upon heating and cooling. The transient peak temperature does not depend on measurement frequency, whereas the peak height is roughly proportional to the inverse frequency of measurements according to Landau's theory for the second order transitions. Calorimetry and magnetometry techniques recorded the same temperature range for the D03 ↔ B2 phase transition as mechanical spectroscopy and in situ neutron diffraction. The study of amplitude dependent internal friction (ADIF) revealed that the absolute value of maximum damping Qm−1 in the SC sample is about five times higher than that of in the PC sample at room temperature. The calculated value of internal stresses opposing magnetic domain wall motions for the PC sample is ∼1.5 times larger than that of for the SC sample, which corresponds to the detrimental influence of grain boundaries to magnetomechanical damping. By increasing the tightening force of torque wrench, a higher level of localized stress is induced to the sample, and the damping capacity (Qm−1) in single cantilever configuration of forced bending vibrations reduces monotonously.