Grain-Growth Kinetics and Thermal Stability of Nanocrystalline Materials

摘要

An essential step in the development of nanocrystalline materials for technological application is understanding the growth kinetics of nanometer-sized grains. Although several studies of such materials find growth exponents and activation-energy values similar to those of polycrystalline materials of conventional grain size, theoretical considerations predict a change in the qualitative nature of the growth kinetics in the submicron size range. Experimental evidence for grain-size-dependent kinetics in nanocrystalline Fe is presented and discussed. The thermal stability of nanocrystalline materials can be improved using the same strategies for grain-boundary pinning that are successful at conventional grain sizes. Alternatively, one can exploit the thermodynamics of chemical segregation to the boundaries to reduce the driving force for grain growth. The effectiveness of this approach is demonstrated for nanocrystalline Pd containing 20 at.% Zr.