Role of disclinations and nanocrystalline state in the formation of quasicrystalline phases on mechanical alloying of Cu-Fe powders

Elemental powders of Cu and Fe were ball milled for various time durations up to 100 h. The various stages of forced alloying by ball milling, leading to instability of elemental crystalline phases and formation of quasicryst alline phases were monitored using X-ray diffraction. Diffusion of Fe into the Cu matrix is proposed as the cause which triggers the instability of cr ystalline phases and leads to the formation of quasicrystalline phases afte r 10 h of milling. Milling for 100 h resulted in two different quasicrystal line phases with different lattice constants. Role of the nanocrystalline m icrostructure as an important criterion for the destabilisation of crystall ine phases is explained. It is suggested that the formation of nanocrystall ine microstructure and their subsequent transformation into quasicrystallin e phases may be associated with a continuous increase in the disclination c ontent of the system, which had formed as a result of continued milling and mechanical deformation.