MICROSTRUCTURAL EVOLUTION IN MECHANICALLY ALLOYED NB-25 AT -PERCENT GE

The microstructural evolution of mechanically alloyed Nb-25 at. % Ge powders has been studied by analytical electron microscopy. Mechanical alloying involves the mixing and milling of powders with different compositions in a high-energy ball mill. During this process, individual powder particles repeatedly cold-weld to other particles upon impact and are subsequently fractured by further milling. The cold-welding (which involves the formation of clean interfaces and possibly interdiffusion at somewhat elevated temperatures just after impact) may produce a zone of intermediate composition. This process is somewhat akin to the formation of transfer layers during wear and erosion.