Formation of new Cu-based nanocrystalline powders by mechanical alloying technique

Nanocrystalline Cu50Mg30Ni20 and Cu50Mg45Ni5 alloys were synthesized by mechanical alloying from mixtures of pure crystalline Cu, Mg and Ni powders using a Fritsch planetary ball mill with certain weight ratio of ball to powder. Structural evolution and thermal properties of these alloys were examined by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray diffraction patterns were examined with the help of Fullprof program by employing Rietveld refinement technique. According to the present results, the crystallite size of Cu–Mg–Ni powders decreased with increasing milling time. Average crystallite size was calculated by three methods; Rietveld refinement technique, Debye Scherrer equation, TEM observation and, it was determined in the range of 10–20 nm. After 25 h of milling nanostructured three phases such as Cu-based solid solution (Cbs), Mg0.85Ni0.15 and MgO were obtained. The lattice parameter of the Cbs phase varied from 3.61 to 3.66 Å during different stages of milling from 5 to 25 h. DSC traces of the mechanically alloyed Cu–Mg–Ni powders showed two exothermic peaks after being milled for 10–15 h.