Effect of cryo-rolling on mechanical properties and microstructure of pure copper

It is a challenging task to achieve high strength without any loss in its electrical conductivity in pure copper because commonly used strengthening mechanisms such as alloying, grain boundary strengthening, and dislocation, result in an increase in strength but simultaneously reduce its electrical conductivity. However, if strengthening is achieved by introducing twin boundaries, then the reduction in electrical conductivity is minimal. These twin boundaries can be introduced in pure copper by low-temperature plastic deformation. Thus, the main objectives of the present research work are to understand the evolution of the microstructure and the resulting mechanical property correlation during liquid nitrogen temperature (LNT) deformation and to compare it with room temperature (RT) deformation. For profile rolling analysis, copper is subjected to profile rolling at both RT and LNT rolling processes to a true strain of 1.77 with a step size of 0.11% strain. High-resolution electron backscatter diffraction coupled with orientation image mapping technique and transmission electron microscopy are used for microstructural characterization of the profile-rolled copper samples. The microstructural characterization reveals mechanical twins of 10–100 nm thickness in samples subjected to LNT, whereas there are no traces of mechanical twins in RT samples. The mechanical characterization by tensile test and hardness test shows that the samples deformed at LNT conditions have superior properties compared to RT.