Microstructural Evolution and Mechanical Properties of Heavily Cold-Rolled and Subsequently Annealed Cu-3 wt.%Ti Alloys with Nano-Lamellar Structure

Abstract

Changes in the microstructure and mechanical properties of Cu-Ti alloy sheets during cold rolling and subsequent annealing were studied with and without Cu-Ti precipitates in the initial microstructures. Pre-existing Cu-Ti precipitates plastically deformed and severely elongated in 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. Vickers hardness increased with decreasing lamellar boundary spacing. Subsequent annealing after cold rolling clearly enhanced the mechanical properties, and a maximum Vickers hardness value of 443 HV (4.35 GPa) was attained in the sample with pre-existing precipitates strained to 6.7. These results suggest that pre-existing precipitates promote microstructural refinement during heavy cold rolling, and that heavily cold-rolled Cu-Ti alloys exhibit anneal hardening behavior, leading to excellent mechanical properties.