Mechanical alloying (MA) is a powder metallurgy processing technique involving cold welding fracturing and rewelding of powder particles in a high-energy ball mill. This has now become an established commercial technique in producing oxide dispersion strengthened (ODS) nickel- and iron-based materials. The technique of MA is also capable of synthesizing non-equilibrium phases such as supersaturated solid solutions metastable crystalline and quasicrystalline intermetallic phases nanostructures and amorphous alloys. In this respect the capabilities of MA are similar to those of another important non-equilibrium processing technique viz rapid quenching of metallic melts. however the science of MA is being investigated only during the past ten years or so. The technique of mechanochemistry on the other hand has had a long history and the materials produced this way have found a number of technological applications e.g. in areas such as hydrogen storage materials heaters gas absorber fertilizers. catalysts cosmetics and waste management. The present talk will concentrate on the basic mechanisms of formation of non-equilibrium phases by the technique of MA and these aspects will be compared with those of rapid quenching of metallic melts. Additionally the variety of technological applications of mechanically alloyed products will be highlighted.

Nanocrystalline materials, with a grain size of typically <100 nm, are a new class of materials with properties vastly different from and often superior to those of the conventional coarse-grained materials. These materials can be synthesized by a number of different techniques and the grain size, morphology, and composition can be controlled by controlling the process parameters. In comparison to the coarse-grained materials, nanocrystalline materials show higher strength and hardness, enhanced diffusivity, improved ductility/toughness, reduced, density, reduced elastic modulus, higher electrical resistivity, increased specific heat, higher coefficient of thermal expansion, lower thermal conductivity, and superior soft and hard magnetic properties. Limited quantities of these materials are presently produced and marketed in the US, Canada, and elsewhere. Applications for these materials are being actively explored. The present article discusses the synthesis, structure, thermal stability, properties, and potential application of nanocrystalline materials.