Magnetoacoustic and Barkhausen emission in ferromagnetic materials

Abstract

Magnetoacoustic emission (MAE) and Barkhausen emission (BE) have been studied in ferromagnetic materials placed in a magnetic field, varying at a few millihertz. Comparison of the two signals indicates the nature of the domain walls responsible for the activity at a given field strength. In order to characterize a specimen the strength of the emission around the hysteresis loop is measured. The technique has been used to measure non-destructively the effects of the following. ( a ) Precipitates: both MAE and BE are sensitive to the growth of precipitates in Incoloy 904, and can be used to monitor the precipitate size. ( b ) Dislocations: BE and MAE exhibit high sensitivity to plastic deformation, and this has been studied in a-Fe. ( c ) Radiation: neutron irradiation of an Fe-Cu alloy produces small changes in emission, although with sufficient sensitivity for useful characterization of radiation effects. ( d ) Tensile stress: MAE is sensitive to stress over the whole range, but particularly at low stresses. Such measurements lay the foundation for the use of MAE for residual-stress measurements.

Prediction of the Mechanical Properties of P91 Steel by Means of Magneto-acoustic Emission and Acoustic Birefringence

“…Various non-destructive methods have been used to evaluate material degradation due to creep [1][2][3][4][5][6][7]. Among them one can indicate a magnetoacoustic emission technique [2,3] or Barkhausen noise method [4,5] for example.…”

“…The magnetoacoustic emission (MAE) technique is based on the analysis of acoustic signals generated in the bulk of the material subjected to alternating magnetic fields [7]. MAE is generated during the movement of non-180 • domain walls (in the case of steels they are 90 • domain walls) as a result of local deformations (volume changes) induced by the local change of magnetisation in a material having the non-zero magnetostriction [8].…”

“…Taking into account a good sensitivity to the precipitation process development [7,12] as well as stress variation [8], the magnetoacoustic emission was chosen in this research.…”

Magneto-acoustic emission for the characterisation of ferritic stainless steel microstructural state

“…The magnetic domain walls get pinned or held in place by dislocation interactions. Because of increased domain-wall dislocation interactions at increased plastic deformation, the magnetising force is not high enough to set them free and reduced domain movement results in decreased BN [21]. This also results in increased hardening of the material with increased strain.…”

Structural Characteristics at Surface and Barkhausen Noise in Aisi 4340 Steel After Grinding

“…of the noise signals connected with the magnetic domain wall movement and with the nucleation of the domains themselves, In materials with positive magnetostriction (like steels) Barkhausen noise increases or decreases by increasing tensile or compressive residual stresses respectively [1,2], Calibration curves of BN versus stress are given in the bibliography [1]; these curves are valid only for specific structures, Effects of microstructure and intergranular impurity segregation, due to tempering, on BN have been examined by Kameda et at. [3,4,5]; the dependence of BN on surface decarburation has been considered by Mayos et al [6], who have resolved the contributions to BN of pearlite and of ferrite; effects of subboundary formation and of dislocation density have been analysed by Klesnil et al [7] and by Kronrnuller [8], From a comparative study of the effects on BN of tensile stresses, precipitates and dislocations, Buttle et al [9] have drawn the conclusion that for practical 256 P. GONDI ET AL monitoring by BN of stressed regions allowance has to be made for accompanying variations of the local microstructure.…”