Micro-magnetic non-destructive testing on extreme condition aged samples
Résumé
Creep phenomenon is an important feature to assess in extreme condition applications, although the correlations with microstructure and magnetic behaviour remain unclear. Conventional Eddy current testing has been extensively used for the ferromagnetic materials characterization but when it comes to creep damage detection, it becomes difficult to distinguish between the changes caused by the actual creep damage and from the signals generated by other sources like, cracks, surface roughness, hardness etc.
In this work, 12%Cr-Mo-W-V creep test samples are investigated using three electromagnetic inspection techniques. Magnetic parameters based on the results are then evaluated in comparison to the microstructure. Additionally, a modified Jiles-Atherton model has been used to numerically reproduce experimental results from Magnetic Incremental Permeability (MIP), Magnetic Barkhausen Noise (MBN) and standard B(H) measurements. All the three techniques exhibit different responses in understanding creep and the modelling parameters derived from the adapted Jiles-Atherton model parameters are then correlated to the microstructure information. Some suitable parameters are then shortlisted according to the application technique. Coupling between the stress and magnetic field is the main and important feature of the ferromagnetic materials consisting of various small magnetic domains in its microstructure
[1][2]. Magnetic Incremental Permeability (MIP) is used to investigate samples as it is highly sensitive to stress.
On the other hand, Magnetic Barkhausen Noise being sensitive to the mechanical changes in the materials, is also used to analyse the samples in addition to standard B(H) curve measurements. Finally, ferromagnetic hysteresis models such as dry friction quasi static model [3], Preisach model [4], JilesAtherton model [5], which are based on magnetic induction B versus applied magnetic field strength H, are implemented to get the simulated data based on experiments. The objectives of these simulations are to improve magnetic signatures interpretations in co-relation to microstructure.