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Understanding how interfaces influence the mechanical behaviour of metallic multilayers has become fundamental to the rational design of materials at nano-scale. In this paper, we explore the effect of loading direction on the mechanical response of a V/Fe bi-layer with semi-coherent interfaces and single crystals, during in-plane uniaxial tension and compression using molecular dynamics simulations.

In the V/Fe bilayer system, tensile loading results in an apparent strengthening in comparison with the V single-crystal due to the simultaneous plastic deformation of both layers; dislocation slip originating from the decomposition of the <100> misfit dislocations into 1/2<111> dislocations inside the V layer and twinning/anti-twinning in Fe. In contrast, plastic deformation during compression initiates in the vanadium layer via a structural phase transition, while iron layer, on the other hand, undergoes slip activation after the decomposition of misfit dislocations inside it.

This tension-compression asymmetry is driven by differences in the shear strain evolution at the interface for both loading conditions. Interfacial shear strains in the V layer is dominant under tension, facilitating the decomposition of misfit dislocations inside the V layer. Whereas, higher interfacial shear strains occur in the Fe layer under compression leading to the decomposition of misfit dislocations inside the Fe layer. Similar observation is seen for V/Fe multilayers with different modulation periods λ. This study provides novel insights into the role of semi-coherent interfaces in controlling tension–compression asymmetry in nanoscale metallic multilayers.