Anomalous weakened annealing-induced hardening in extremely fine nanograined NiFe alloys

Annealing-induced hardening effect was studied in electro-deposited nanocrystalline Ni and NiFe thin films. Nanoindentation testing showed obvious hardening effect for all grain sizes in experiment, which were precisely controlled by adding Fe solutes. Contrast to the general trend in which the hardening effect monotonically increases with decreasing grain size, it enhanced firstly, peaking at a critical grain size (similar to 16 nm) and then lowered. Based on the apparent inverse H-P trend and unusual enhancement of strain rate sensitivity after annealing, we attributed the weakened annealing-induced hardening phenomena, despite of the strongest grain boundary pinning effect resulted from the highest Fe solutes (up to 50 at%), mainly to the more pronounced grain-boundary mediated plasticity in extremely fine nanograins. This work contribute directly to understanding the distinct effect of alloying on mechanical properties of nanocrystalline metals. (C) 2022 Published by Elsevier B.V.

Automated summary

This study investigated the annealing-induced hardening effect in electro-deposited nanocrystalline Ni and NiFe thin films. The results showed that the hardening effect does not increase with decreasing grain size, but rather peaks at a critical grain size before decreasing. This can be attributed to the more pronounced grain-boundary mediated plasticity in extremely fine nanograins.