Cu-Cr nanocrystalline powder prepared by high-energy ball milling

Nanocrystalline Cu-50%Cr composite powders were prepared by high-energy ball milling. Effects of ball milling time and process control agent (PCA) on the grain size, microstructure and morphology of the composite powders were studied using X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and transmission electron microscopy (TEM). A thermodynamic model was also applied to predict the change in the solubility limit of the Cu-Cr system. The results show that the powders are refined at a highest rate without the addition of PCA, but the powder yield is lower. However the excess of PCA would weaken the grain refinement. On this conditions, the optimum addition of PCA is 5% (mass fraction). With increasing milling time, the grain size of the powders decreases gradually, while the micro-strain increases firstly then decreases correspondingly. After milling for 60 h, the nanocrystalline Cu-50%Cr composite powders with homogeneous distribution of Cu and Cr phase are achieved with average grain size of about 10 nm and the solid solubility of Cr in Cu is extended largely up to 7%.