Structure and mechanical properties of copper/niobium multilayers
- Los Alamos National Lab., NM (United States). Center for Materials Science
Copper/niobium multilayers prepared by sputtering onto Si substrates with layer thicknesses ranging from 11 to 5,000 {angstrom} have been characterized by transmission electron microscopy and nanoindentation. The films are strongly textured with {l_brace}110{r_brace} close-packed planes of the bcc Nb parallel to the {l_brace}111{r_brace} close-packed planes of the fcc Cu and close-packed directions tending to be parallel as well. For the 11 {angstrom} layers, the Cu is found to grow pseudomorphically on Nb in the bcc structure. It is thought that, for thicker layers, the bcc Cu loses coherency and transforms martensitically to the fcc phase, thus resulting in the observed Kurdjumov-Sachs orientation relationship. As the layer thickness, d, decreases from 5,000 to 500 {angstrom}, the hardness increases as d{sup {minus}1/2}; i.e., it follows a Hall-Petch relationship so that hardening is due to grain boundaries and interfaces. The slope is the same as in pure Cu, but there is a large intercept which is ascribed to internal stresses and a large dislocation density. As the layer thickness decreases from 100 to 11 {angstrom}, the hardness increases as (1/d) {ell}n (0.69d), which is a line tension formulation such as would be expected for Orowan dislocation bowing between the layers. Again there is a large intercept which is ascribed to cutting through the Cu/Nb interfaces. The interfacial energy is calculated to be 0.46 J/m{sup 2}.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 529533
- Journal Information:
- Journal of the American Ceramic Society, Vol. 80, Issue 7; Other Information: DN: Paper presented at the symposium on microstructure-property relations of advanced materials, April 29--30, 1996, Stuttgart (DE); PBD: Jul 1997
- Country of Publication:
- United States
- Language:
- English
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