Effect of prior cold work on mechanical properties and structure of an age-hardened Cu-1.5wt% Ti alloy

The effects of prior cold work on hardness, tensile properties, electrical conductivity and microstructure of an aged Cu-1.5 wt% Ti alloy have been studied by employing hardness and resistivity measurements, tensile tests and scanning and transmission electron microscopy. The hardness increased from 80 VHN in the solution-treated condition, to 210 VHN on peak ageing and 280 VHN with prior cold work followed by ageing. While a similar trend has been observed in yield and tensile strengths, the ductility (percentage elongation) decreased from 45% to 9%. The electrical conductivity of the alloy also increased up to 26% International annealed copper standard upon ageing the cold-worked alloy. Maximum strengthening of the alloy was associated with the precipitation of metastable, coherent and ordered Cu-4 Ti, beta' phase having body-centred tetragonal structure. The differences in the properties and microstructural evolution between low and high titanium alloys (for example, the absence of composition modulations and deformation twins in Cu-1.5 Ti alloy, while they are present in Cu-4.5 Ti alloy) have been discussed. Prior cold work did not change the fracture mode of microvoid coalescence.