Mechanically induced driving forces in preparing W-Cu nanocomposite

Mechanical alloying (MA) is a versatile technique to produce different nanocrystalline and amorphous alloys. The ability of producing immiscible elements is one of the specific advantages of this method. High energy shaker ball milling has been used to produce W-20 wt.% Cu nanocomposite. Powders of elemental W (1-30 mu m) and Cu (1-15 mu m) were milled with a ball to powder ratio (BPR) of 16:1 for up to 30 h. The size and shape of the elemental and alloyed particles were examined by a scanning electron microscope (SEM). It has been observed that 30 h of milling produced homogeneous structure. X-ray diffraction (XRD) patterns confirmed partial alloying of Cu and W. As the sizes of W and Cu atoms are different, elastic strain energy due to misfit has been calculated to be about 5.3 kJ/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) 2008 Elsevier B.V. All rights reserved.