An investigation of thermal stability and microhardness of electrodeposited nanocrystalline nickel-21% iron alloys

The thermal stability of an electrodeposited nickel-21% iron alloy with an average grain size of approximately 14 nm was investigated. Samples were annealed for 90 mins in the temperature range of 373-773 K. The results of this study showed that grain growth started after annealing at and above 400 K. Two regimes of grain growth were identified. It is suggested that the low temperature regime (below 575 K) is accommodated mainly by the grain boundary diffusion, while the high temperature regime is assisted by the lattice diffusion. The microhardness results also confirm the presence of these two regimes. The position of the (111) XRD peaks indicated a sudden decrease in the lattice parameter after annealing at 773 K, which is attributed to the loss of connectivity of the nanosize grains. The variation of hardness with grain size followed the Hall-Petch relationship. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.