Ultra-high local plasticity in high-strength nanocomposites

We subjected an aged Cu-24wt%Ag ingot to cold drawing to create a high-strength nanostructured composite wire with both Cu-rich proeutectic and Ag-rich eutectic components. During the drawing, a fine lamellar structure (average spacing 20 ± 6 nm) developed in the proeutectic component, which contained a high density of Ag fibers (average width below 5 nm) embedded in the matrix. In the eutectic component, a relatively coarse structure developed, with an average Ag grain size around 100 nm. The result of such a bimodal size of Ag fibers was ultra-high bending plasticity, i.e., the drawn wire tolerated 59% bending strain at the outermost edge, 15 times its tensile elongation (3.6%). During our bending test, dynamic recovery and partial recrystallization occurred more near the inner edge than near the outer edge and primarily in the eutectic component. High bending strain caused some of the thicker Ag fibers to become discontinuous and lose their original alignment. This structural evolution increased local plasticity, resulting in an unexpectedly high achievable bending strain, which is unusual in nano-sized, Ag-fiber-reinforced high-strength composites.