Microstructure and strain in electrodeposited Cu/Ni multilayers
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Microstructure and strain in electrodeposited CuyNi multilayers David van Heerden Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
Emil Zolotoyabko and Dan Shechtman Department of Materials Engineering, Technion-Israel Institute of Technology, 32000 Haifa, Israel (Received 31 October 1994; accepted 27 June 1996)
Electrodeposited CuyNi multilayers with different modulation lengths L 4–18 nm were examined by means of x-ray diffraction and transmission electron microscopy. Preferred orientations of [111], [110], and [001]-types, as determined from relative x-ray diffraction peak intensities, were seen in the multilayers. By means of computer simulations of the measured x-ray diffraction spectra, several parameters of the multilayers, such as L-values and fluctuations DL, as well as lattice strain, were determined. Multilayers having large L were found to be fully relaxed due to interfacial dislocation formation. In short L [001]-texture multilayers partial strain relaxation occurs, probably due to the incorporation of Cu into the Ni layers. Both of the processes lead to the diffuse CuyNi interfaces. Short wavelength multilayers with a [111]-preferred orientation were almost fully strained. The importance of the [111]-texture in the improvement of mechanical strength of CuyNi multilayers resulting from its enhanced ability for stain accommodation is discussed.
I. INTRODUCTION
Microlayered metallic materials have recently become the subject of considerable interest both because they possess anomalous, and potentially useful, mechanical properties and because these properties can be readily tailored by altering the relative layer thicknesses (see, e.g., Refs. 1–3). While the vast majority of multilayered materials are produced by sputtering or vapor deposition, electrodeposition techniques that produce high quality multilayers have also been devised.4–7 The mechanical property/layer thickness relationship for electrodeposited and vapor deposited multilayers have been the subject of numerous studies (see, e.g., Refs. 3, 5, 7–10). It was found that the ultimate tensile strength (UTS) of a two-element multilayer is dependent upon the combined thicknesses of two adjacent layers, i.e., the modulation wavelength L. The value of L at which the maximum strength occurs in vapor deposited CuyNi multilayers is typically L 2 nm with layers of equal thickness (see, e.g., Ref. 8). In electrodeposited CuyNi multilayers the maximum UTS increases with increasing Ni content; for a multilayer where the ratio of the Cu : Ni layer thicknesses is 1 : 9 the maximum UTS occurs at L 20 nm.5,7 Foecke and Lashmore3 argued that the difference in behavior between electrodeposited and vapor deposited multilayers may arise from the enhanced epitaxy associated with electrodeposition, and suggested that the peak in the mechanical properties occurs at the wavelength at which the interface between J. Mater. Res., Vol. 11, No. 11
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