Effects of microstructure of ferromagnetic alloys on magnetoacoustic emission

The origin of MAE (magnetoacoustic emission) is mainly due to the interaction between 90° magnetic domain walls and defects, as evidenced by the phase lag of the MAE with respect of magnetic induction B(t), found under certain conditions. Recent experiments have shown an asymmetry of MAE bursts in a period corresponding to a half cycle of the hysteresis loop for embrittled HY80 steel samples, which was not explained satisfactorily. The present study was performed to investigate fully the origin of this asymmetry with an improved scheme of AC magnetic field application. The results show that critical information on the material characteristics can be obtained directly from the shape of MAE spectra and that the asymmetry is reduced by increasing the AC field intensity. It has also been found that the generation of a square wavelike form of dB/dt is desirable to enhance the rate of data collection at low AC field frequency