Tensile Properties of Nanostructured Ni‐Cu Multilayered Materials Prepared by Electrodeposition

Abstract

As the layer thicknesses in 90% Ni-10% Cu multilayered alloys electrodeposited from a sulfamate bath are decreased, the ultimate tensile strength peaks at 1100 MPa for 6-7 nm Cu layers, and then decreases to about 1000 MPa as the Cu layer thickness reaches 1 nm. This decrease in deposit strength is associated with a reduction in the deposit (100) texture caused by the influence of Cu, which has a (110) preferred orientation in the sulfamate system. The results suggest that highly coherent nanostructured multilayers can only be deposited from a single electrolyte if the preferred orientation for the two metals is the same.In spite of the considerable interest in multilayered metal structures generated by the report of greatly enhanced mechanical properties for materials with ultrathin layers (1), the origin of the observed effects is still not clearly understood (2). One difficulty has been that the vacuum-deposited materials generally used are of insufficient quality and are too thin, 1-2 ~m, for reliable measurements (3). Work in our laboratory has resulted in a method for electrodeposition of multilayered metals (4), which has recently been refined so that thick specimens, 50 i~m, with extremely reproducible properties can be prepared (5).In the present paper, the effect of layer thickness on the tensile properties of 90% Ni-10% Cu multilayer materials electrodeposited from a sulfamate electrolyte is discussed in terms of the deposit structure as investigated by x-ray diffraction. Such materials have been shown previously (4, 5) to exhibit an approximately twofold enhancement in tensile strength for sufficiently thin layers. This enhancement may result from grain refinement associated with the layered structure in accordance with the Hall-Petch relationship (6-8), or be attributable to restricted dislocation movement across alternating layers of materials with high and low elastic constants, as proposed by Koehler (9). ExperimentalDetails concerning the specimen preparation and tensile test procedures are given in previous publications (4, 5). Specimens were electrodeposited at 45~ via concerted modulation of the cathode potential and rotation rate from a commercial nickel sulfamate bath (Barret SN) containing 5 mM copper sulfate. The cathode was a 25 mm diam x 13 mm long stainless steel mandrel, sandwiched between chlorofluorocarbon end pieces, to which a 2 ~m thick Cu basal layer was applied from a standard additive-free pyrophosphate bath at 45~ Pure Cu layers were plated at -0.14 V vs. saturated calomel electrode (SCE) with cathode rotation at 750 rpm, and Ni layers containing 0.8% Cu were plated at -105 mA/cm 2 from the stagnant bath. The nominal compositions reported, usually 90% Ni-10% Cu, do not take into account the 0.8% Cu codeposited during Ni deposition.Plated foils were nominally 50 ~m thick and were fashioned into dogbone specimens having a reduced section width of 6.3 mm and a gage length of 2.8 cm. Tensile testing was performed at room temperature at a cross head speed of 0.1 mm/min, and strain ...

Electrodeposition and Characterization of Alloys and Composite Materials

“…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.…”

“…The dependence of the tensile properties of multilayered Cu-(Ni-Cu) deposits, with the nominal overall composition 90 at.% NiÀ10 at.% Cu, was investigated in the work of Tench and White [108] as a function of the Cu layer thickness (varying from 1 to 15 nm). Multilayers of the nominal thickness of 50 μm were deposited from a commercial sulfamate bath with the addition of 5 mM CuSO 4 .…”

Mechanical Properties of Nanostructured Metals

“…This section focuses on nanoscale metallic multilayer thin films with h < 50 nm. Techniques to measure yield strength and hardness include microindentation [135], nanoindentation [157][158][159][160][161][162][163][164][165][166], tensile testing [167][168][169], and micropillar compression testing [112,113,164,[170][171][172]. However, these techniques focus on the composite yield strength.…”

“…Recent work by Gram et al outlines an elevated temperature X-ray diffraction-based technique to measure individual layer stress caused by the thermal expansion mismatch between a Cu-Ni multilayer thin film and a Si substrate [173]. Cu-Ni [136,160,167,170,174] and Cu-Nb [110,112,113,157,164,175] are treated separately here due to extensive work on these two systems. The remaining metal-on-metal composite systems are treated afterward.…”

Microstructures and Mechanical Properties of Nanostructured Copper-304 Stainless Steel Multilayers Synthesized by Magnetron Sputtering

“…When the interfaces are semi-coherent, the spacing of the misfit dislocations at the interface reduces with increasing lattice parameter mismatch. In some systems, a drop in strength, or softening, is observed [ 1,[11][12][13] when the layer thickness is below a few nanometers. The mechanisms for this softening, however, are not well understood.…”