Soft magnetic Cu–Co–Ni composite materials produced by mechanical alloying, cold compaction and sintering

Cu90Co10 and Cu85Co10Ni5 soft magnetic alloys were obtained by non-equilibrium phase synthesis. Elemental powder mixtures were mechanically alloyed in a planetary mill to disperse ultrafine Co and (Co, Ni) particles in the copper matrix. Thus, it was possible to modified magnetic properties of these materials. Resulting powders were characterised as a function of milling time by means of X-ray diffraction, SEM, high resolution transmission electron microscopy and electron probe microanalysis. The variation of magnetic properties and its dependence on the structure/precipitation change with milling time for each alloy are discussed. Magnetic properties of Cu-Co and Cu-Co-Ni powders reached their optimum values after milling for 60 h. On the other hand, superparamagnetic behaviour was observed at 300 K in the Cu-Co-Ni alloys. Both alloys were consolidated after 60 h milling by cold compaction and sintering at 973 K for 1 h. Although this treatment is performed at high temperature, precipitation and coalescence of Co particles on the Ni5CoXCu952-X system was retarded by the presence of Ni in solid solution in Cu matrix.