Effects of Be Content and Heat-Treatment Conditions on the Heterogeneous Nanostructure and Mechanical Properties of Cu-Be Alloys

The effects of beryllium (Be) content and heat-treatment conditions on the development of the heterogeneous nanostructure and mechanical properties of CuBe alloys were systematically examined. With increasing Be concentration from 0.4 to 2.14 mass%, the volume fraction of eye-shaped twin domains developed in the 90% cold-rolled samples increased up to 4.9%. Additionally, the volume fraction further increased to 7.1% when Co was excluded, even for a Be concentration of 1.86 mass%. Therefore, Be addition promotes mechanical twinning, while the precipitates appear to impede it. Furthermore, it was revealed that excess Be was consumed for formation of γ- and β-phases in the CuBe alloy with 2.14 mass% Be. The age hardenability at 588 K was more significant with increasing Be content, although the increase in tensile strength was not highly significant. These tendencies were more significant when the alloy was solution treated at higher temperatures and for longer times. The highest tensile strength (1.7 GPa) was observed for the CuBe alloy with 2.14 mass% Be when tested along the transverse direction, which was slightly higher than the 1.5 GPa measured along the rolling direction. The above results indicated the important role of age hardenability and the volume fraction of eye-shaped twin domains in the heterogeneous nanostructure.