Magnetomechanical Damping in Thermally Sprayed Fe-Cr-X Coatings

Abstract

The ability of high damping capacity iron-chromium based coatings to absorb mechanical vibrations has been investigated over a wide range of frequencies varying between ∫= 10Hz to 10 kHz, and deformation amplitude between ϵ = 10-6to 10-3. The magnetomechanical hysteresis loss (Q-1) was determined based on the modal analysis technique of a flat beam and was found to be very sensitive to internal stress in the samples. Heat treatments usually enhanced the loss capability, but only high-temperature annealing of coatings restored the whole damping capacity to be comparable to that of cast alloys of same chemical composition. The variation of Q-1 versus vibration amplitude first increased rapidly, passed through a maximum, and then declined relatively slowly to its initial values. The position of the maximum damping was shifted towards lower strains with annealing time and temperature. In contrast to the strain amplitude, the vibration frequency did not influence damping behavior significantly, as expected in ferromagnetic materials. The structure of magnetic domains was observed using the magnetooptical Kerr effect Modification of structure following heat treatments was associated with different values of the damping capacity. Accordingly, the beneficial effect of annealing on damping capacity arises on the one hand from improved mobility of unpinned domain walls and on the other hand from growth of 90 deg domains, leading rather to equiaxed domain configurations. The irreversible movement of domain walls upon application of an external stress in general occurred suddenly and abruptly between two pinned positions.