Double-peak age strengthening phenomenon and mechanism of Cu–Be–Ni–Co alloys

Abstract

Unconventional double-peak age strengthening phenomenon has occasionally been observed in some alloys, yet the underlying mechanism responsible for this phenomenon are still unclear. Here, we for the first time report the double-peak age strengthening phenomenon in the Cu–Be–Ni–Co alloys and try to unveil the underlying mechanism. Both the theoretical and experimental analyses demonstrate that the strong coherency strengthening effect of tiny nanoprecipitates (<1 nm) contributes significantly to the appearance of first peak, whereas the order-to-Orowan strengthening transformation accounts for the appearance of second peak. Moreover, the precipitate evolution processes of the alloys are identified as Guinier–Preston (GP) zones → γ′′→ γ′ and the light-mass Be atoms in the γ′ phase are directly made out by using integrated differential phase-contrast scanning transmission electron microscopy (iDPC-STEM) technology. Our work may provide new insights into the coherency strengthening effects and demonstrates a powerful strategy for designing high performance via double-peak behavior.

Keywords

• Cu–Be alloys
• Double-peak age strengthening
• Precipitate evolution
• Strengthening mechanism
• Be atomic image