Distortion Analysis of Magnetic Excitation (DAME) is a novel and simp le measurement approach for... more Distortion Analysis of Magnetic Excitation (DAME) is a novel and simp le measurement approach for evaluation of different properties of ferrom agnetic materials. The presence of a different ferromagnetic material, between the poles of a n electromagnetic (EM) yoke, introduces non-linear distortion in the excitation v oltage (VE) across the coil around the EM yoke. The non-linear distortion behav iour of the magnetic excitation voltage (V E) is directly influenced by the magnetisation behaviour of the ferromagnetic material between the poles of the EM yoke. Th e time derivative of the excitation voltage (dV E/dt) plotted as a function of total applied voltage (VT) (which is directly proportional to the applied magnetic field) has been found to show unique shape for each sample with different material cond itions. The shape of the DAME profile with a peak and trough clearly reflects the sub tle changes in the composition, microstructure, grain orientation and stress through their effe...
In ferromagnetic materials, the magnetic Barkhausen emission (MBE) during magnetization has been ... more In ferromagnetic materials, the magnetic Barkhausen emission (MBE) during magnetization has been found to be highly sensitive with good and repeatable correlations to microstructural variations. Thus, MBE technique is complementary to the microscopy techniques and is superior for on-line characterization of ferromagnetic materials. However, this micro-magnetic non-destructive evaluation (NDE) technique could not be developed, so far, to a level of resolving and quantifying the individual microstructural features such as grain size and second phase precipitate size which vary simultaneously during heat treatment or thermal aging. In the present study, it has been shown that, in a carbon steel, on carefully optimizing the experimental parameters, the MBE profile systematically changes from a single peak to two peaks, when the quenched martensite structure dominated by high dislocation density is heat treated to produce well differentiated ferrite grain boundaries and second phase precipitates. The first MBE peak at lower current/magnetic field has been attributed to the influence of grain boundaries and the second MBE peak at higher current/magnetic field to that of second phase precipitates. To substantiate this, it has also been shown that the variations in the position of the two MBE peaks match well with the kinetics of tempering, the changes in the average size of the grains and carbides. The excellent quantitative correlation reveals that MBE technique has matured as a powerful technique for rapid on-line evaluation of metallurgical quality of as fabricated and service exposed ferromagnetic materials through finer microstructural characterization. .
Distortion Analysis of Magnetic Excitation (DAME) is a novel and simp le measurement approach for... more Distortion Analysis of Magnetic Excitation (DAME) is a novel and simp le measurement approach for evaluation of different properties of ferrom agnetic materials. The presence of a different ferromagnetic material, between the poles of a n electromagnetic (EM) yoke, introduces non-linear distortion in the excitation v oltage (VE) across the coil around the EM yoke. The non-linear distortion behav iour of the magnetic excitation voltage (V E) is directly influenced by the magnetisation behaviour of the ferromagnetic material between the poles of the EM yoke. Th e time derivative of the excitation voltage (dV E/dt) plotted as a function of total applied voltage (VT) (which is directly proportional to the applied magnetic field) has been found to show unique shape for each sample with different material cond itions. The shape of the DAME profile with a peak and trough clearly reflects the sub tle changes in the composition, microstructure, grain orientation and stress through their effe...
In ferromagnetic materials, the magnetic Barkhausen emission (MBE) during magnetization has been ... more In ferromagnetic materials, the magnetic Barkhausen emission (MBE) during magnetization has been found to be highly sensitive with good and repeatable correlations to microstructural variations. Thus, MBE technique is complementary to the microscopy techniques and is superior for on-line characterization of ferromagnetic materials. However, this micro-magnetic non-destructive evaluation (NDE) technique could not be developed, so far, to a level of resolving and quantifying the individual microstructural features such as grain size and second phase precipitate size which vary simultaneously during heat treatment or thermal aging. In the present study, it has been shown that, in a carbon steel, on carefully optimizing the experimental parameters, the MBE profile systematically changes from a single peak to two peaks, when the quenched martensite structure dominated by high dislocation density is heat treated to produce well differentiated ferrite grain boundaries and second phase precipitates. The first MBE peak at lower current/magnetic field has been attributed to the influence of grain boundaries and the second MBE peak at higher current/magnetic field to that of second phase precipitates. To substantiate this, it has also been shown that the variations in the position of the two MBE peaks match well with the kinetics of tempering, the changes in the average size of the grains and carbides. The excellent quantitative correlation reveals that MBE technique has matured as a powerful technique for rapid on-line evaluation of metallurgical quality of as fabricated and service exposed ferromagnetic materials through finer microstructural characterization. .
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