Structure of thermal-aging induced Fe clusters and their effects on physical properties for Cu-1.2 at.% Fe alloy

We have investigated the structure of Fe clusters which were induced by thermal-aging and their effect on magnetic properties of Cu-1.2 at.% Fe alloy by using the extended X-ray absorption fine structure (EXAFS), the atom probe tomography (APT) and the SQUID magnetometer. Small Fe clusters with the diameter of 3.3 nm on average and solute Fe atoms in the solution-treated specimen show paramagnetism. At the initial stage of thermal-aging, Fe clusters with the diameter of 10.9-24.0 nm on average are produced, and most of them exist as anti-ferromagnetic γ-Fe with fcc structure due to the coherent growth against the fcc Cu matrix. By the enough long time thermal-aging, some of these γ-Fe clusters transform to ferromagnetic Fe clusters with bcc structure due to their growing up to enough large size. From the results obtained by EXAFS, the atomic fraction of Fe atoms forming bcc-structured clusters indeed increases with increasing the aging time. These results obtained by non-destructive EXAFS methods revealed that transformation from γ-Fe to bcc-structured Fe occurs only by the thermal-aging. The effects of the Fe clustering on the electrical resistivity and the micro Vickers hardness, and effects of the plastic deformation will also be mentioned briefly.