Formation of multiple twins and their strengthening effect in nanocrystalline Cu/Zr multilayer films

Multiple twins are experimentally observed within Cu grains in nanostructured Cu/Zr multilayer films. Formation of the multiple twins occurs through the sequential emission of partial dislocations not only from the grain boundaries but also from the Cu/Zr interfaces, which are driven by extremely high internal stresses and highly complex stress state caused by the inhomogeneous microstructures. The multilayers with multiple twins exhibit hardness higher than those with single or coplanar twins, indicative of a significant strengthening effect of the multiple twins.