Structures, properties and responses to heat treatment of Cu-Y alloys prepared by mechanical alloying

Cu_100-xY_x (x=5, 10 and 20 wt. %) alloys were synthesized from elemental powders using mechanical alloying for different durations up to 40 h. The as-milled powder samples were heat treated for 2 h at 300 and 500°C. These samples were characterized by scanning and transmission electron microscopy (SEM and TEM, respectively), X-ray diffractometry, microhardness testing and particle size analysis. Nano-sized αCu grains were found by TEM analysis in all compositions after milling for 20 h by TEM analysis. Both SEM and particle size analyzer confirmed the flattening of the particles into thin discs after milling for 2 h and their size decreased on further milling, reaching a minimum after milling for 10 h and increased significantly after milling for 20 h. No Y or secondary phases were detected by XRD for Cu₉₅Y₅ after milling for 20 h. However, a small amount of Cu₅Y/Cu₄Y was found in the same sample by TEM. The microhardness values increased with milling time, reaching a maximum for powder sample that had been milled for 20 h for Cu₉₅Y₅ and 40 h for Cu₉₀Y₁₀ and Cu₈₀Y₂₀ respectively. Heat treatment at 500°C for 2 h on the Cu₉₅Y₅ powders which had been milled for 20 h produced no significant coarsening of αCu grains as the size of these grains was still in the nanometer region. However, the amount of Cu₅Y/Cu₄Y as detected by TEM was found to increase upon heat treatment.