Precipitation hardening of Cu-Ti-Cr alloys

Abstract

The effect of 1.0 wt.% chromium addition on the age hardening behaviour of Cu-3Ti and Cu-4Ti alloys was studied with respect to mechanical properties, electrical conductivity (EC) and microstructure. It was observed that Cu-Ti-Cr alloys are predominantly strengthened by precipitation hardening mechanism. The hardness of Cu-3Ti-1Cr alloy (118 Hv10 in solution treated condition) increased to 277 Hv10 on peak aging while that of Cu-4Ti-1Cr alloy increased from 224 to 326 Hv10. A similar trend was observed for the yield and tensile strength values of both the alloys, though the ductility (%elongation) decreased on aging. The electrical conductivity of Cu-3Ti-1Cr and Cu-4Ti-1Cr alloys in solution treated condition was 5.9 and 3.9%IACS, respectively. On peak aging the conductivity increased to 13.1%IACS for the Cu-3Ti-1Cr alloy and 8.8%IACS for the Cu-4Ti-1Cr alloy at 450 °C. Maximum strengthening of the alloys was associated with the precipitation of metastable, ordered and coherent β′ (Cu4Ti) phase on peak aging. The alloys overaged due to the precipitation of β (Cu3Ti) phase. Discontinuous precipitation leading to the precipitation of Cu3Ti was also observed in alloys overaged at 450 and 500 °C. © 2004 Elsevier B.V.All rights reserved.