Alloying of immiscible Ge with Al by ball milling

Mechanical alloying (MA) is a versatile technique to produce nanocrystalline and amorphous alloys. Its special advantage is to form alloys of immiscible elements. High energy planetary ball milling has been used to produce Al-2 wt.% Ge alloy. Powders of Al (1-125 mum) and Ge (0.5-2 mum) were milled together with a powder to ball weight ratio of 1:20 up to 400 h. The size and shape of the elemental and alloy powder particles were examined in a scanning electron microscope (SEM) while their microanalysis was performed by energy dispersive system (EDS) attached with SEM. It has been observed that 300 h of milling produces homogeneous alloy. X-ray diffraction (XRD) patterns confirm complete alloying of Ge with Al. As the size of the atoms of Al and Ge are different, elastic strain energy because of misfit has been calculated to be about 2.6 kcal/mol. It has been concluded that among the factors contributing towards the enthalpy, stress exerted by dislocations on solute atoms is the major driving force for alloying. (C) 2003 Elsevier Science B.V. All rights reserved.