Application of equal-channel angular pressing to Cu–Co alloy with ferromagnetic precipitates

Experiments were conducted to evaluate the influence of equal-channel angular pressing (ECAP) on the magnetic properties of a Cu-1.8 wt.% Co alloy containing 0.2 wt.% Cr which forms ferromagnetic Co-rich precipitates in the Cu matrix after aging treatment. Coherent face-centered-cubic precipitates were formed by isothermal aging at 873 and 1073 K for 259 ks. The two different aging temperatures gave precipitates of different sizes, which were expected to show either single-domain or multidomain structure. In the case of small precipitates, one pass of ECAP was effective to improve coercivity, but further pressings tended to decrease coercivity and saturation magnetization due to random orientation and dissolution of the precipitates. In the case of large precipitates, shape change to increase coercivity is difficult. Saturation magnetization was increased by the demagnetizing effect of the precipitates. Electron holography provided the quantitative magnetization measurements for rounded cubic and elongated Co precipitates, indicating the increased in-plane magnetization of the elongated precipitate due to the demagnetizing effect as a result of deformation.