Pulsed Eddy Current Testing of Thermally Aged and Cold-Rolled Fe–Cu Alloys

In this work, Fe-1wt%Cu alloy samples exposed to thermal aging and cold rolling (CR) were studied as an attempt to emulate material degradation in neutron irradiated nuclear reactor pressure vessels. CR was tested by pulsed eddy currents (PECs) using a directional probe which was rotated in the sample plane. Normalized PEC signals, represented by typical “figure of eight” on the polar plot, showed very strong anisotropy, which has a monotonic dependence on the amount of cold work. Since the normalized PEC signals represent the response due to electrical conductivity and reduce the ferromagnetic effect, it is concluded that the change is due to anisotropic magnetoresistivity of the rolled steel. The normalized difference PEC responses have been found to be described by the quadratic dependence of the cosine of in-plane angle shifted by an angle, which is believed to correspond to slip planes of dislocations induced by rolling. The technique advantageously combines effects of rolling on electrical conductivity and magnetic permeability and does not require referencing to an untreated standard, which is important for future material and device health management.