Evolution and Stability of a Nanocrystalline Cu₃Ge Intermetallic Compound Fabricated by Means of High Energy Ball Milling and Annealing Processes

Abstract

In this study, the structural evolution of two nanostructured Cu-22 wt pct Ge (Cu-20 at. pct Ge) and Cu-26 wt pct Ge (Cu-24 at. pct Ge) alloys upon mechanical alloying (MA) with subsequent heat treatment was investigated, and the phase transitions were monitored by means of various characterization methods. The findings indicated that, when the MA process continued for some time, a nanocrystalline α-Cu(Ge) solid solution was formed, which partially transformed into an amorphous phase. Further MA processing for 20 hours led to the formation of a disordered nanometric ε-Cu₃Ge intermetallic compound with a monoclinic crystal structure. Increased milling time subsequently led to the diminishing of the content of the amorphous phase which transformed into ε-Cu₃Ge nanocrystals. Clearly, a nanocrystallization transformation occurred upon ball milling principally on account of the accumulated energy due to the heavy mechanical deformation. Crystallization was also seen to occur at 473 K (200 °C) after annealing the MA-ed powders, leading to the formation of an ordered ε ₁-Cu₃Ge intermetallic phase with an orthorhombic structure. The crystallographic relationships between the two disordered and ordered intermetallic phases were also discussed.