Two-stage Hall-Petch relationship in Cu with recrystallized structure

Although Cu was studied extensively, the Hall-Petch relationship was mainly reported in the coarse-grained regime. In this work, fully recrystallized Cu specimens with a wide grain size regime of 0.51-14.93 mu m manifest a two-stage Hall-Petch relationship. There is a critical grain size of 3 mu m that divides stages I and II where the Hall-Petch slope k value are quite different. The stage II is supposed to be validified down to 100 nm at least by comparing with a Cu-Ag alloy. The critical grain size varies in different materials systems, and the underline mechanisms are discussed based on the dislocation glide modes. (C) 2020 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.