Grain size stabilization and strengthening of cryomilled nanostructured Cu 12Â at% Al alloy

Nanocrystalline Cu12 at% Al alloy was synthesized by high energy ball milling under cryogenic condition. The alloy was then annealed up to 900 °C (or 0.87 Tm). Phase and microstructural evaluation were carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM) and the mechanical property was investigated by microhardness testing. Results show that at elevated temperatures grain growth of Cu 12 at% Al alloy is much less than pure Cu prepared under same condition. The microhardness of the alloy decreases from 2.91 GPa to 2.73 GPa (∼6% decrease) after annealing at 900 °C. Superior thermal stability at high temperature was ascribed to the grain boundary pinning by nano-scale intermetallic particles. Kinetically stabilized grain size and hardness show good agreement with theoretical predictions.