Cu–Ni–Si系合金のヘテロナノ組織の発達に及ぼす析出物の影響

抄録

The effects of the existence of precipitates on the development of heterogeneous–nano (HN) structure in a Cu–Ni–Si system alloy were systematically investigated using a Cu–4.0 mass％Ni–1.1 mass％Si alloy. After solution treatment, the specimens were aged at 733 K for various periods up to 10.8 ks and then cold–rolled to a reduction of 93％ in thickness. The microstructure and mechanical properties of the rolled specimens were examined. After 70％ cold rolling, the specimens with the aging for 3.6 ks, the HN structure consisting of conventional lamellae parallel to the rolling direction, shear bands inclined from an angle to the rolling direction and deformation twin domains surrounded by the shear bands were well–developed. On the other hand, the HN structure formed in the specimen without the aging before the cold rolling was relatively vague. The HN structure developed more clearly in the specimens with increasing the rolling reduction. However, the area fraction of the twin domains in the 3.6ks–aged specimen cold–rolled to 93％ were decreased compared with the 70％ cold–rolled one. The microhardness of the alloy accordingly decreased from 307 Hv to 290 Hv. It is inferred that the shear bands were formed more densely in the 3.6 ks–aged specimens than in the un–aged specimen due to the precipitation strengthening as well as the more significant work hardening during the cold rolling. The more densely developed shear bands could cause the subdivision of the twin domains and thus result in a decrease in the area fraction of the twin domains and hardness in the specimen cold–rolled to 93％.