Thermal stability of electrodeposited nanocrystalline Ni–Co alloys

Reducing the grain size of Ni electrodeposits to below 100 nm has considerable potential for MEMS applications. However, the strong thermodynamic potential for grain growth in these nanocrystalline materials may be a limiting factor in their widespread use. This study investigates the possibility of increasing the thermal stability of nanocrystalline Ni electrodeposits by alloying with Co. It is found that while alloying does improve the thermal stability, the largest single factor is the sulphur impurity concentration. This can be interpreted in terms of a dynamic segregation model in which the migrating abnormal growth fronts collect sulphur as they sweep through the nanocrystalline matrix.