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 Cu100−xNbx (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 10 wt.% Nb by MA at RT. The Cu crystallite size decreases with increasing milling time, and approaches 7 nm in Cu80Nb20 and 13 nm in Cu95Nb5 after 100 h milling, respectively. The maximum value of microhardness is about 4.8 GPa for Cu80Nb20 milled for 100 h. 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.