Abstract
Magnetic Barkhausen noise (MBN), hysteresis measurements, first order reversal curves (FORC), Vickers microhardness, and Transmission Electron Microscopy (TEM) analyses were performed on Fe-1wt.%Cu (Fe-Cu) samples isothermally aged at 700°C for 0.5 – 25 hours to obtain samples with different sized Cu precipitates and dislocation structures. Fe-Cu is used to simulate the thermal and irradiation-induced defects in copper-containing nuclear reactor materials such as cooling system pipes and pressure vessel materials. The sample series showed an initial increase followed by a decrease in hardness and coercivity with aging time, which is explained by Cu precipitates formation and growth as observed by TEM measurements. Further, the MBN envelope showed a continuous decrease in its magnitude and the appearance of a second peak with aging. Also, FORC diagrams showed multiple peaks whose intensity and location changed for different aging time. The changes in FORC diagrams are attributed to combined changes of the magnetic behavior due to Cu precipitate characteristics and dislocation structure. A second series of samples aged at 850°C, which is above the solid solution temperature of Fe-Cu, was studied to isolate the effects of dislocations. These samples showed a continuous decrease in MBN amplitude with aging time although the coercivity and hardness did not change significantly. The decrease of MBN amplitude and the appearance of the second MBN envelope peak are attributed to the changes in dislocation density and structure. This study shows that the effect of dislocations on MBN and FORC of Fe-Cu materials can vary significantly and should be considered in interpreting magnetic signatures.
Highlights
INTRODUCTIONFe-1wt%Cu was heat treated at high temperature (700◦C and 850◦C) for different durations to induce formation of copper-rich precipitates (CRP) and/or changes in dislocation structure that simulate the thermal and irradiation-induced defects in copper-containing nuclear reactor steels
In the U.S, many of the existing reactors are reaching or exceeding their 40 year operation license
Magnetic Barkhausen noise (MBN), hysteresis measurements, first order reversal curves (FORC), Vickers microhardness, and Transmission Electron Microscopy (TEM) analyses were performed on Fe-1wt.%Cu (Fe-Cu) samples isothermally aged at 700◦C for 0.5 – 25 hours to obtain samples with different sized Cu precipitates and dislocation structures
Summary
Fe-1wt%Cu was heat treated at high temperature (700◦C and 850◦C) for different durations to induce formation of copper-rich precipitates (CRP) and/or changes in dislocation structure that simulate the thermal and irradiation-induced defects in copper-containing nuclear reactor steels Reactor components such as the cooling system pipes and the reactor pressure vessel materials contain copper, as it enhances the mechanical properties in steel.[13,14] irradiationand thermally-induced CRP formation is one of the main causes of embrittlement in reactor materials.[13,15] In this study, MBN measurements, major loop hysteresis, FORC, TEM, and hardness tests were investigated to look for correlations between the microstructure, magnetic signatures, and mechanical properties
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