Abstract
It is one of the most characteristic behaviors of Cu-4 wt%Ti alloy that a sharp decrease in electrical resistivity and an increase in mechanical strength are observed at the initial stage of ageing. The precipitation sequence from the supersaturated solid solution of Cu-Ti alloy is thought to be: modulated structure→intermediate phase (face centered tetragonal, c⁄a=0.98)→stable precipitate, Cu3Ti.
The decrease in electrical resistivity is discussed according to Kolomets’ theory which calculates residual resistivity on the assumption of a periodical distribution of solute concentration. The increase in strength, which is expected form the modulated structure, is found to be due to the internal strain hardening mechanism originally suggested by Mott-Nabarro.
An intermediate phase sustains both electrical and mechanical properties of this alloy. The grain boundary reaction type or the Widmanstätten type of precipitate Cu3Ti, however, leads to softening.
