2020 年 59 巻 1 号 p. 260-264
Changes in microstructure and mechanical properties of Cu–Ti alloy sheets during cold rolling were studied with Cu–Ti precipitates in the initial microstructures. Second phase particles, which are presumably β–Cu4Ti precipitates, were observed in the Cu–Ti alloy before cold–rolling along the grain boundaries, and their Ti concentration and size are near 7 wt.％ and are less than 1μm. Pre–existing Cu–Ti precipitates were plastically deformed and severely elongated along the rolling direction via cold rolling, accelerating the formation of a nano–lamellar structure. A mean lamellar boundary spacing of 20 nm was achieved at an equivalent strain of 6.7. This exceptional refinement during cold rolling can be mainly attributed to pre–existing precipitates, which can effectively subdivide the matrix microstructure. Ultimate tensile strength, 0.2％ proof stress and Vickers hardness increased with decreasing lamellar boundary spacing, following the Hall Petch relationship. Therefore, the strength of heavily deformed Cu–Ti sheets can be primarily attributed to grain boundary strengthening related to the lamellar boundaries. These results suggest that pre–existing precipitates promote microstructural refinement during heavy cold rolling, leading to excellent mechanical properties.
