Tensile behavior and flow stress anisotropy of accumulative roll bonded Cu-Nb nanolaminates

Abstract

The flow stress, ductility, and in-plane anisotropy are evaluated for bulk accumulative roll bonded copper-niobium nanolaminates with layer thicknesses ranging from 1.8 μm to 15 nm. Uniaxial tensile tests conducted parallel to the rolling direction and transverse direction demonstrate that ductility generally decreases with decreasing layer thickness; however, at 30 nm, both high strengths (1200 MPa) and significant ductility (8%) are achieved. The yield strength increases monotonically with decreasing layer thickness, consistent with the Hall-Petch relationship, and significant in-plane flow stress anisotropy is observed. Taylor polycrystal modeling is used to demonstrate that crystallographic texture is responsible for the in-plane anisotropy and that the effects of texture dominate even at nanoscale layer thicknesses.

Tensile deformation and fracture mechanisms of Cu/Nb nanolaminates studied by in situ TEM mechanical tests

“…The mechanical properties of these thin films have been studied by means of nanoindentation and micropillar compression tests, and the information obtained from these investigations has been used to determine the dominant deformation mechanisms [1,12]. It is nowadays widely accepted that the flow strength of MNLs with thick layer thicknesses (h) > 50 -100 nm is controlled by the formation of dislocation pile-ups at the interfaces [18,19]. This mechanism is inhibited for smaller layer thicknesses (5 -10 nm < h < 50 -100 nm) because of the lack of space to form the dislocation pileups and confined layer slip (CLS) becomes the dominant process [20][21].…”

“…However, not all metallic materials are amenable to be processed into nanolaminates by ARB because it is not always possible to thin down the layers to the nm scale without breaking the continuity due to the onset of strain localization in the layers upon severe plastic deformation. Successful examples of MNLs manufactured by ARB include Cu/Nb, Cu/Ta and Cu/V [3,19,[25][26][27][28][29]. Bulk samples of MNLs manufactured by ARB have been tested in tension parallel to the layers [19,27] to assess the effect of layer thickness on the strength and ductility, which are important parameters from the viewpoint of engineering applications.…”

“…Successful examples of MNLs manufactured by ARB include Cu/Nb, Cu/Ta and Cu/V [3,19,[25][26][27][28][29]. Bulk samples of MNLs manufactured by ARB have been tested in tension parallel to the layers [19,27] to assess the effect of layer thickness on the strength and ductility, which are important parameters from the viewpoint of engineering applications. Bulk tensile testing perpendicular to the layers was, however, not possible due to the small thickness of the ARB sheets.…”

“…Bulk tensile testing perpendicular to the layers was, however, not possible due to the small thickness of the ARB sheets. It was found that the strength increased as the layer thickness decreased [19,27] and that the MNLs deformed in the transverse direction (TD) were stronger and presented higher strain-to-failure than those tested in the rolling direction (RD) [19]. However, the actual deformation and fracture mechanisms responsible for this behaviour were unknown because they cannot be ascertained in the fractured samples due to the nm scale of the relevant microstructural dimensions.…”

Neutron reflectometry investigations of interfacial structures of Ti/TiN layers deposited by magnetron sputtering

“…">INTRODUCTIONIt has long been realized that interfaces play a critical role in the structural properties of nanolayered composites [1][2][3][4]. Over the years, the aim in engineering interfaces has been to radically improve several structural properties simultaneously, such as strength, ductility, and fracture toughness [5,6]. In this pursuit, intense research has been dedicated toward better understanding of how interfaces govern the interactions and reactions of discrete defects generated during deformation.…”