A study on the effect of dislocation on the magnetic properties of nickel using magnetic NDE methods

Dislocations affect the magnetic properties of ferromagnetic materials by pinning the domain walls. The primary mechanism is interaction between the stress fields of dislocation and domain walls. Using magnetic nondestructive methods, namely the acoustic Barkhausen noise (AB), magnetic Barkhausen noise (MB), and the hysteresis curves, we have studied these interactions. The three measurements give different types of information. AB provides information about non‐180° type domain wall interaction, MB primarily provides information about 180° domain wall interaction, and the hysteresis curve about both these interactions as well as about rotation of domain walls. The paper presents results obtained on polycrystalline nickel which was first deformed and then annealed at different temperatures in order to achieve different dislocation densities. The results show that AB and hysteresis loss follow the same trend as hardness. MB results, however, change in a more complex fashion which is sensitive to grain recrystallization as well as dislocation structure. Interesting features of these results will be discussed in detail.