Effect of Strain on Melting Point of Lead produced by Mechanical Milling

In the past two to three decades, mechanical milling (high intensity milling of materials of stoichiometric composition and occuring without any material transfer) as a means of synthesis of nano-crystalline materials has gained importance. It is a "top-down" approach wherein the coarse grain size of a bulk material is reduced by mechan-ical stresses unit it reaches nanometer dimensions. Grain size refinement by mechanical milling can be applied to pure materials including metals, alloys and intermetallic compounds [1-3]. The minimal grain size achieved by mechanical milling in metals and intermetallic compounds has been reported to be in the range of 3 to 30 nm depending on the material and processing conditions[4]. The nature of deformation and fracture during milling depends upon whether the fracture strength of the mater-ial is significantly higher than the yeild strength as in ductile materials, the impact forces cause flattening by plastic deformation, cold welding, work hardening and subsequent fracture whereas in brittle materials, fractur-ing and size refinement occurs more readily without much of plastic deformation[4]. The energy stored during the process of mechanical milling manifests through a variety of crystal defects such as vacancies, anti site disorder, dislocations, fresh surfaces, increased grain boundaries, stacking faults and structural disorder.