Thermal stability of ultrafine grained and nanocrystalline metals

The aim of this work is to figure out the conditions for enhanced thermal stability of nanocrystalline structures. For this purpose ultrafine grained elemental and alloyed metal powders were prepared by the inert gas condensation technique. Cu- Ag- CuAg- and AgAu-wire was evaporated. The as-consolidated materials were investigated by transmission electron microscopy and differential scanning calorimetry. It turned out that in pure metals (Ag, Au, Cu, Pd) abnormal grain growth occurs leading to large grained 'islands'embedded in nanocrystalline material after moderate annealing conditions. On the other hand when using alloying elements the grain growth is homogeneous throughout the specimen. The size of the exothermic reactions in alloys suggest that dissolution phenomena are existent in binary metal alloys prepared by inert gas condensation