Effects of milling time on structural and magnetic properties of Cu10wt%Co15wt%Nb₃sn Alloys consolidated by hot pressing

In this work, Cu-Co-Nb magnetic composite alloys were obtained by hot-pressing under argon atmosphere of an alloy prepared by mechanical mixing. For the preparation of this powder master alloy, it was mixed 15wt% of intermetallic Nb₃Sn, synthesized by mechanical alloying of elemental Nb and Sn and subsequent thermal treatment, and a Cu-10wt%Co solid solution, also prepared by mechanical alloying of elemental Cu and Co. A laboratory mill working at 250 rpm under argon atmosphere during 5 and 10h was used to disperse ultrafine Nb₃Sn particles into the copper-10wt%Co matrix. Microstructure of resulting powders and consolidated materials were characterized by means of X-ray diffraction, scanning electron microscopy, and electron micro probe analysis. Magnetic properties and mechanical properties were measured by means of a vibrating sample magnetometer and a durometer, respectively. Fitting of the X-ray diffraction patterns with the Rietveld method, revealed that during the hot pressing process, the Nb₃Sn particles reacted with cobalt to form (Co,Sn)₂Nb, liberating some Sn that difussed in Cu forming a Cu-Sn solid solution. The influence of the milling time on this structural change and the associated variation of magnetic properties are discussed.