Structure evolution and solid solubility extension of copper-niobium powders during mechanical alloying

The supersaturated Cu-Nb solid solutions were produced by mechanical alloying (MA) at room temperature (RT). The microstructural evolution and mechanical property of Cu_100-xNb_x (x=5, 10, 15, 20, wt.%) powder mixtures during milling were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) observations and microhardness measurement. The results show that the solid solubility limit of Nb in Cu can be extended to more than 10wt.% Nb by MA at RT. The Cu crystallite size decreases with increasing milling time, and approaches 7nm in Cu₈₀Nb₂₀ and 13nm in Cu₉₅Nb₅ after 100h milling, respectively. The maximum value of microhardness is about 4.8GPa for Cu₈₀Nb₂₀ milled for 100h. The mechanism of solid solubility extension by MA was discussed using a thermodynamical analysis. The surface and elastic strain energy produced by milling supply the main driving force for alloying.