Characterization of copper-cementite nanocomposite produced by mechanical alloying

A copper-iron carbide nanocomposite has been synthesized by high-energy milling of elemental powders (Cu69-Fe23-C8), followed by annealing at 873 K. Phase identification and microstructure characterization have been carried out by transmission electron microscopy and energy dispersive spectroscopy. The carbide phase found in the as-milled material has been identified as Fe3C and/or Fe7C3, but clearly only Fe3C was present after annealing. Overall, grain sizes ranged from 10 to 50 nm in the as-milled condition and from 30 to 160 nm after annealing, with the carbide phase presenting a higher growth rate than copper. Stacking faults and a dispersion of Cu nanoparticles (5-10 nm) have been detected in annealed cementite while copper grains exhibited twins on {1 1 1} planes. Cementite growth could be evaluated in terms of precipitate growth theory. The remarkable thermal stability of the copper matrix is proposed to be related to solute drag effects.