Hardness, ductility, and thermal processing of Cu/Zr and Cu/CuZr nanoscale multilayer foils

The hardness, ductility, and thermal processing of Cu/Zr and Cu/CuZr multilayers were investigated by indenting, bending, and heating a series of free-standing multilayer foils. The foils were deposited with alternate, nanoscale layers of Cu and Zr, and then thermally processed to produce three additional nanostructures: alternate layers of Cu and amorphous CuZr(aCuZr); alternate layers of Cu and Cu51Zr14; and a non-layered structure with small Cu grains in large Cu9Zr2 grains. The hardness and ductility of the foils depended strongly on the degree of thermal processing and varied dramatically with the volume fraction of the Zr or CuZr phases in each of the four nanostructures. The dependence of hardness on volume fraction was stronger when the films were indented parallel to their layering than when the foils were indented perpendicular to their layering. This result demonstrates that plastic deformation is anisotropic in these multilayer samples.