Age hardening studies in a Cu–4.5Ti–0.5Co alloy

Age hardening in a Cu–4.5Ti–0.5Co alloy has been studied at different aging temperatures and times. It has been observed that this alloy exhibits considerable age hardening with hardness increasing from 225HV to a peak value of 320HV on aging. Yield strength increases from 360 to 710 MPa and tensile strength from 610 to 890 MPa on aging the solution treated alloy for peak strength. The electrical conductivity of the alloy is found to be 4 and 8% International Annealed Copper Standard (IACS) in solution treated and peak aged conditions, respectively. Addition of cobalt to Cu–4.5Ti alloy reduces the aging temperature and time for attaining peak hardness. Ordered, metastable and coherent Cu4Ti (βl) precipitate is found to be responsible for maximum strengthening of the alloy. Interestingly, absence of equilibrium precipitate Cu3Ti and presence of Cu4Ti phase have been noticed in the overaged condition. The absence of Cu3Ti is attributed to the addition of cobalt. In addition, intermetallic phases of Ti and Co like Ti2Co and TiCo have been observed in solution treated, peak aged and overaged conditions. Cold work prior to aging enhances the hardness, strength and electrical conductivity of the alloy. For example, 90% cold work followed by aging at 400°C for 1 h increases the hardness from 320 to 430HV; yield and tensile strengths, from 710 to 1185 and 890 to 1350 MPa, respectively, and electrical conductivity, marginally by 1% IACS. While mechanical properties are comparable, electrical conductivity of Cu–4.5Ti–0.5Co is less than that of the binary Cu–4.5Ti alloy in the solution treated as well as peak aged conditions.