High thermal stability of mechanically-alloyed nanocrystalline Cu-Nb alloys

The high thermal stability of a nanocrystalline mechanically-alloyed Cu-Nb alloy was studied by means of isothermal annealing at high temperatures. The structure of the Cu matrix remains nanocrystalline with a grain size of about 50 nm even after annealing at 1000 degrees C for 10 h. The copper grain growth is described with the help of kinetic analyses. The activation energy of the copper grain growth in Cu-10 at. % Nb is about 0.98 eV and the grain growth exponent is 4. The enhanced stability of the nanocrystalline, Cu microstructure is attributed to the diffusion of Nb atoms along the Cu grain boundaries, Zener drag of NbO, Cu2O or Fe7Nb6 particles, and a non-equilibrium state of Cu grain boundaries.