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 μm manifest a two-stage Hall-Petch relationship. There is a critical grain size of 3 μm 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.