Ultra-high strength and plasticity mediated by partial dislocations and defect networks: Part II: Layer thickness effect

Layer thickness dependent mechanical behaviors of metallic nanolaminates have been extensively investigated. In a recent study [1], we show that a particular defect network, consisting of layer interface, stacking faults and twin boundaries, plays an important role in achieving high strength in Cu/Co multilayers. Here, we report a follow-up study on the effect of layer thickness on this unique interplay of defect networks. To this end, we investigate the mechanical behavior of highly textured Cu (111)/Co (0002) multilayers with individual layer thickness of 5, 25 and 100 nm. In situ micropillar compression tests show that the Cu/Co 25 nm multilayers have a much higher strength than 100 nm and 5 nm multilayers. Post-deformation TEM analyses and MD simulations reveal the layer thickness dependent variations of defect density dominating the strengthening effect in multilayers. This study provides new perspectives on optimal defect networks for the design of high strength, deformable metallic materials.