Wavelength‐Property Correlation in Electrodeposited Ultrastructured Cu‐Ni Multilayers

Abstract

Multilayered foils with 10% Cu-90% Ni and ultrathin (9-2000A) layers have been fabricated by electrodeposition. The anodic passivity of Ni and the irreversibility of the Ni/Ni z+ reaction permit alternate deposition of each metal layer from a common electrolyte. SEM, TEM, and x-ray diffraction analysis indicate discrete layer formation and a (100) textured structure. A maximum in the tensile strength and electrical resistivity of these foils was detected at a wavelength of 200A (20A Cu + 180A Ni). The maximum tensile strength obtained (1900 MPa) is over 3 and 4.5 times greater than that for homogeneous Ni and Cu foils and exceeds the maximum value reported for vacuum deposited foils by 70%.Ultrastructured materials, comprising alternating microlayers of two or more materials, exhibit greatly altered properties relative to the components. The periodic lattice distortion introduced by the artificial composition modulation can generate materials with unique and sometimes enhanced physical and chemical properties. Anomalous effects, which include a maximum at a wavelength (~) of -20A for mechanical and transport properties, have been observed for bimetallic vacuum deposited layered composites (1-3).Electrodeposition has been shown to be a viable technique for fabrication of multilayered composites with discrete layers (4-9). Bimetallic multilayered structures can be conveniently fabricated by alternate reduction of the metal ions from a common electrolyte containing both metals in a ratio of about 1(noble metal):100 (4-9). Electrodeposited Cu-Ni multilayered composites exhibited enhanced tensile strength as the Cu + Ni layer thickness (or k) was decreased to 100 nm (6). This paper explores the dependence of tensile strength and resistivity as the layer thickness approaches atomic dimensions. The deposition technique has been extended to permit fabrication of free-standing Cu-Ni composites with an order of magnitude thinner layers. The deposit properties are evaluated by x-ray diffraction, SEM/EDX, TEM, tensile testing and electrical conductivity measurements. ExperimentalThe Cu-Ni foils were electrodeposited on an Inconel rotating cylinder from a Ni-sulfamate bath (80 g/liter Ni, 40 g/ liter H3BO3, 0.15 g/liter Na-dodecyl sulfate) to which CuSO4 was added as required. Bath pH was 3.8. A 0.5 ~m thick Ni basal was initially deposited to eliminate structural patterns of the polycrystalline substrate. Cu and Ni layers were then alternately deposited with synchronous modulation of the electrode rotation speed and the deposition current (or potential). The electrode rotation rate, current density, periodicity, and atomic percent of the respective metals were varied with a HP-9826 computer interfaced with a PAR-173 potentiostat/galvanostat. Cathode dimensions and cell configuration, and other plating parameters were as described in Ref. (6). The foil thickness, which ranged from 25-50 ~m, was measured with a digimatic micrometer. Individual layer thickness was determined from the amount of charge passed and verified using a...

Electrodeposition and Characterization of Alloys and Composite Materials

“…As can be seen maximum hardness for the deposit containing Cu/NiÀ100 layers was achieved at the thickness of individual layers of 12 nm. These results are not in agreement with those detected for evaporated layers Cu/NiÀ111 [116], where the maximum hardness was obtained for individual layer thickness of 1.6 nm, indicating that, most probably, the hardness depends on the thickness and the total surface area of In several investigations the influence of the individual layer thickness on the tensile strength was reported [106,114,116,117]. The results of these investigations are presented in Fig.…”

“…Following mechanical properties were mainly investigated: Young's modulus [98], hardness [115], and tensile strength [107,[115][116][117]. It is shown that all investigated properties depend on the thickness of the individual layers and that in all cases multilayered structures showed better properties than that of pure metals and/or their alloys.…”

“…1.46 The hardness of the deposit containing Cu/Ni À 100 layers as a function of the thickness of individual layers (Reprinted from [115] with the permission of Elsevier) Fig. 1.47 The tensile strength of the multilayered deposits as a function of the thickness of individual layers: open circle- [107]; open square- [117]; open triangle- [118]; open inverted triangle- [108] (Reprinted from [109] with the permission of Elsevier) mainly the consequence of different parameters of the deposition process (bath composition, pulse regimes, temperature, etc.). A common explanation for the decrease of tensile strength with the increase of individual layer thickness (after the maximum value) is the increase of the coherence of the intermediate layer.…”

Microstructural and Mechanical Characterization of Multilayered Iron Electrodeposits

“…In a review of the mechanical properties of electrodeposited multilayers, Ross (1994) cited numerous studies which have shown an enhancement in the tensile strength of multilayers as the layer thickness decreases. Additionally, Menezes and Anderson (1990) have observed the tensile strength of electrodeposited copper/nickel multilayers with a repeat layer (nickel + copper layer) thickness of 20 nm to be 3 and 4.5 times greater than that for homogeneous nickel and copper electrodeposits, respectively. The enhanced tensile strength is attributed to the presence of interfaces and the finer microstructure of multilayered electrodeposits (Ross 1994).…”

Size effect on mechanical behavior of Al/Si3N4 multilayers by nanoindentation

“…Metal/metal multilayers systems have been already intensively investigated, and it was found that there is a remarkable lengthscale effect on the mechanical properties and mechanical strength increases with decreasing individual layer thickness [8,9,. For example, the mechanical strength of Cu/Ni multilayers exceeds 2 GPa with an individual layer thickness of a few nanometers [8,[40][41][42], is clearly larger than that of their counterparts with bulk form composition (mechanical strength in the range of 10-50 MPa), and is also clearly larger than the calculated value according to the rule-of-mixtures. Generally, the smaller grain size and thickness and the larger area of the interface limit the dislocation motion, leading to the increase of the mechanical strength in the multilayers with smaller layer thicknesses.…”