Fabrication of Dual-Phase Strengthened Cu–Ti Alloy Sheets

Abstract

The advancement of electronic devices and their capabilities has driven the demand for specific material property combinations, such as mechanical strength and electrical conductivity, in materials pertinent to device fabrication. To this end, the microstructure and properties of Cu–4.2 at% Ti alloy sheets, produced through a multi-step process involving over-aging and severe cold rolling, were investigated. The microstructure of the over-aged alloy prior to cold rolling consisted of cellular components with laminated plates of terminal copper solid solution (Cu_ss) and β–Cu₄Ti. When the over-aged alloy was severely cold rolled for a 99% reduction in thickness, a hierarchical double-phase microstructure was formed parallel to the cold-rolling direction, with Cu_ss bands and two-phase bands containing small β–Cu₄Ti pieces stacked within Cu_ss phase. The strength of the over-aged alloy sheet increased steadily during increasing degrees of cold rolling, caused by a large volume fraction and fine dispersion of hard β–Cu₄Ti pieces and high dislocation density in the Cu_ss matrix. The electrical conductivity decreased in the later stages of cold rolling; however, the conductivity was higher than that of the alloy sheet prepared by peak aging and cold rolling. Eventually, the balance between strength and electrical conductivity of this Cu–Ti alloy was significantly improved by over-aging and severe cold rolling compared to conventional peak-aging and cold rolling processes.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 62 (2023) 68–72. Figures 4 and 5 were slightly modified.

(Left) Tensile strength and electrical conductivity in Cu–4.2 at% Ti alloy sheets, prepared by solid solution treatment (squares), peak-aging (circles), or over-aging (circles), then cold-rolled from a 10 mm thickness to 0.3, 0.2, and 0.1 mm. (Right) Cross-sectional FE-SEM images of Cu–4.2 at% Ti alloys after over-aging and cold rolling from a thickness of 10 mm to 0.3 mm. The brighter and darker regions correspond to the β–Cu₄Ti and Cu phases, respectively. The alloy sheet exhibits a hierarchical double-phase microstructure consisting of laminated Cu bands (with darker contrasts) and two-phase bands containing small β–Cu₄Ti particles suspended in the Cu phase.