CONICET | Buscador de Institutos y Recursos Humanos

Cu1-xCox (x<0.2) was a model system in early investigations related to precipitation phenomena in supersaturated binary alloys. The precipitation sequence involving Co rich clusters and coherent precipitates, which become incoherent with the Cu rich matrix when reaching a critical size has been extensively investigated. This binary alloy is also a paradigm of granular alloys exhibiting giant magnetoresistance, arising from electron scattering processes inside the coherent Co precipitates and/or at their interfaces. More recently, a minimum in the electrical resistance has been reported at low temperature (about 35K), which was attributed to a Kondo-like mechanism involving Co rich clusters or precipitates. In this work, Cu90Co10 alloys are prepared by rapid solidification, in a twin roller melt spinning device, at tangential wheel speeds between 5 m/s and 20 m/s to obtain quite different solute distributions and Co-rich precipitates size distributions directly from the melt. The microstructures resulting for different quenching rates are characterized by electron microscopy, scanning (SEM) and transmission (TEM), and by X-ray diffraction (XRD) techniques. It is found that precipitate spatial and size distributions strongly depend on the quenching rate. Magnetic measurements indicate that there are A paramagnetic and a ferromagnetic contribution to the hysteresis loop. Resistance vs. temperature curves are typical of metallic solids and they show a minimum at low temperature. The precipitation structures observed in the alloys in the as cast condition are correlated with the parameters describing the low temperature resistance minimum.