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 Ni₅Co_XCu_95−X system was retarded by the presence of Ni in solid solution in Cu matrix.