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Characterization of copper precipitates in Fe-Cu alloys by using micromagnetic NDE techniques

: Parlog, M.; Altpeter, I.; Breme, J.; Dobmann, G.

Mazal, P. ; Czech Society for Nondestructive Testing:
Defektoskopie 2002. Proceedings
Brno: Brno University of Technology, 2002
ISBN: 80-214-2247-5
International Conference and NDT Technique Exposition (Defektoskopie) <2002, Liberec, Czech Republic>
Fraunhofer IZFP ()
micromagnetic technique

The copper containing ferritic steels used in pressurized water reactors (PWR) and boiling water reactors (BWR) are known to be prone to hardening and embrittlement by thermal ageing. Preliminary investigations concluded that the changes in mechanical properties are caused by copper-precipitation. Small (2-3 nm diameter) and coherent copper precipitates cause an increase of the hardness, decrease of the fracture toughness and shift of the Charpy impact transition temperature. For a better understanding of these phenomena, 9 Fe-Cu model alloys with Cu content between 0.65 and 2.1 wt. % were manufactured. These samples were characterized by Vickers hardness (HV 10) and electromagnetic methods, and their dependence on the Cu content was investigated. It was observed that the Vickers hardness increases with rising Cu content. Hysteresis measurements showed that the values of coercivity increase with growing Cu content. The coercivity and the Vickers hardness exhibit a similar behaviour with respect to Cu content. Barkhausen noise measurements show that the mean Barkhausen noise amplitude and the width of the Barkhausen noise profile curve at the 25% and 50% of the maximum amplitude decrease with Cu content. Measurements of the induction voltage of an eddy current probe show a decrease with increasing Cu content.