Thermal stability in nanocrystalline electrodeposits - a comparison of Ni- and Co-based materials

Paper in proceeding, 2009

The exceptional properties associated with nanocrystalline materials are to a large extent a result of their high intercrystalline volume fraction. However, the intrinsic instability of the nanostructured state may compromise the gain in properties by the occurrence of grain growth during exposure at elevated temperatures. Thermal stability is therefore a fundamental materials issue for nanocrystalline materials. This paper summarizes findings for Ni- and Co-based materials obtained by a combination of characterization techniques (DSC, XRD, TEM, and Tomographic Atom Probe (TAP)). Alloying as well as phase- and ordering transformations are found to affect the grain growth behavior. The findings for the different materials are the basis for a model in which it is stated that segregation leads to an improved thermal stability of the nanocrystalline structure by the combination of a thermodynamic effect (reduction in driving force for grain growth) and a kinetic effect (reduction in grain boundary mobility).