Microstructure and mechanical properties of Cu_xNb_1-x alloys prepared by ball milling and high pressure torsion compacting

New Cu_xNb_1-x alloys were prepared using a two-step process of ball milling and subsequent high pressure torsion compacting at ambient temperature. The alloys showed a nanocrystalline structure with grain sizes between 13-26 nm for the Cu-rich samples and 11-13 nm for the Nb-rich samples. The grain sizes decreased with the milling time and the amount of Nb in the Cu-rich and Cu in the Nb-rich samples, respectively. The distortion of the crystallographic lattice of the fcc Cu and bcc Nb suggests the formation of a solid solution. The mechanical properties studied by nanoindentation show an increase of the hardness with milling time and the amount of added element. A thermal treatment was carried out under a protective Argon atmosphere. Up to 400 °C the Cu-rich samples do not show significant signs of oxidation and in increase of hardness. The Nb-rich samples showed a continuous increase of the hardness up to 500°C, due to the precipitation of Cu, and the initial formation of NbO_x.