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

Abstract

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 eyeshaped 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 £and ¢-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.

A Basic Research for Conquest Drawbacks and Further Improvement of Properties of Heterogeneous-Nano Structured Copper Alloys

“…Hardness peaks also appeared at temperatures of 523 and 573 K, but the temperatures and the time to reach the hardness peak are lower and shorter than those of common copper alloys, respectively, due to the low thermal stability of the HN. 4,12) In particular, softening occurs early in the specimens with small amounts of added elements. Consequently, precipitation of the additive elements becomes insufficient even after peak aging; therefore, the EC should not increase adequately.…”

“…In other words, recrystallization and softening easily occur before complete precipitation of additive elements in the matrices; hence, the remaining solute elements lower the EC. Therefore, HN materials must be aged at substantially lower temperatures than that of the normal grain-sized ones; 4,13) even in that case, sufficient precipitation by aging is difficult.…”