Using the Rule of Mixtures to Examine the Hardness of Cu/Cu-Zr Multilayers

Abstract

ABSTRACTCu/Cu-Zr multilayer foils were fabricated and indented to determine the degree to which multilayer hardness is enhanced by increasing the volume fraction of the harder phase. Using sputter deposition and thermal processing a series of foils was fabricated in which the thicknesses of the Cu layers remained fixed while the thicknesses of the alternate Cu-Zr layers varied. These samples were then indented both parallel and normal to their layering. In general, hardness increased as the volume fraction of the harder Cu-Zr phase rose. When the films were loaded parallel to their layering, the measured hardnesses were higher and the dependencies on volume fraction of the Cu-Zr phase were stronger than when the films were loaded normal to their layering. These results agree with predictions based on isostress and isostrain theories. The relationships between hardness and volume fraction are used to compare the hardnesses of the Cu-Zr phases: amorphous Cu-Zr, Cu51Zr14 and Cu9Zr2, and to show that the hardness of the textured, as-deposited Zr layers is highly anisotropic .