Precipitation hardening of Cu–Ti–Cr alloys

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.