High tensile ductility via enhanced strain hardening in ultrafine-grained Cu

Low tensile ductility owing to the insufficient strain hardening is the main drawback for ultrafine-grained (UFG) materials, which restricts their practical applications. Here, via a simple friction stir processing technique with additional cooling, we prepared UFG Cu with high strength and tensile ductility. Enhanced strain hardening capacity, which is effective in blocking and accumulating dislocations, was achieved in the present recrystallized UFG microstructure. The enhanced strain hardening capacity is attributed primarily to the low dislocation density, and the presence of large fraction of high angle grain boundaries and a certain amount of coherent twin boundaries. This work provides a strategy for designing UFG materials with good mechanical properties.