Length-scale-dependent mechanical behaviour of Zr/Nb multilayers as a function of individual layer thickness

Nanostructured metallic multilayers systems continue to garner interest because of their promising mechanical properties, exploitable in the field of materials engineering. These novel materials show high yield strengths, anomalous Young's modulus values and even superior radiation tolerance for layer thicknesses up to a few tens of nanometers. However, there are still many unknowns related to the deformation mechanisms operating at the nanoscale because of deformation mechanisms, in this nanoscale, depend directly on the layer thickness and the combination of different or similar crystal structures in the interface. The objective of this work is to produce Zr/Nb multilayers and investigate the dependence of deformation mechanisms when the layer thickness is reduced. Nanoindentation hardness as a function of periodicity, lambda, has been measured for Zr/Nb multilayers. It has been found that for decreasing h the yield strength values, sigma(2.7), do not increase. For lambda=60 nm and lambda=30 nm, sigma(2.7) values are almost constant: 1.97 and 1.93 GPa, respectively, whereas for lambda=10 nm, the yield strength shows a decrease to 1.79 GPa. The mismatch between sigma(2.7) and sigma(CLS) values for any core cut-off, alpha, condition (0.2 and 1) and for any eta ratio (eta= h(Zr)/h(Nb)), indicates that the strain mechanism based on CLS did not occur for any period studied; therefore, the strain mechanism based on IBS is suggested, in accord with the activation of a pyramidal slip system {11 (2) over bar2}((11) over bar 23), along Zr layer, even for thickness up to 30 nm. Thereby, dislocation loop glide is not confined to an isolated layer, changing the plastic behaviour of the nano-multilayer. (C) 2015 Elsevier B.V. All rights reserved.