Interface Structure And In-situ Nanomechanical Testing Of Cu/V Nanoscale Metallic Multilayers

Nanoscale metallic multilayers are widely used as essential components of high-performance microelectronics and microelectromechanical systems due to their excellent mechanical,electric and thermal properties.Deformation and fracture during the manufacture and service processes of nanoscale metallic multilayers have been identified as significant factors which influence their reliability.Therefore,mechanical responses of nanoscale metallic multilayers are of great scientific significance.Despite the great number of researches which focus on the mechanical properties of nanoscale metallic multilayers,few attentions have been given to the uncommon interfaces which possess structures different from typical ones.In this study,transmission electron microscope characterization and energy dispersive X-ray spectroscopy analysis have been conducted to study the interface structure of Cu/V nanoscale metallic multilayers;state-of-the-art in situ transmission electron microscopy is utilized to study the different effects of two kinds of interfaces found in the Cu/V nanoscale metallic multilayers.Cu/V nanoscale metallic multilayers were successfully fabricated by cross accumulative roll boding method.Two different types of bimetal interfaces are observed between Cu and V layers,i.e.the regular sharp interfaces and interfacial transition zones(ITZs).The regular sharp interface possesses an orientation relationship of[011]Cu ?[111]V;while the uncommon ITZs often show up when the Cu and the V layers have orientation relationships of[130]Cu ?[001]ITZ ?[110]V,which contribute to?30%of the total interfaces in the Cu/V multilayers.Atomistic characterizations show that the ITZs possess a body-centered cubic structure with Cu atoms dissolved in V matrix.The formation of such irregular interfaces can be ascribed to the deformation-induced mass transport at the bimetal interfaces.Such uncommon ITZs are also believed to exist in other immiscible bimetal multilayers fabricated by the severe plastic deformation methods,due to the strong mechanical alloying effect.The poor slip continuity also facilitates the formation of ITZ by confining the dislocation interaction and annihilation near the interface.Such dense dislocation activities contribute to the formation of massive amount of vacancies,facilitating the diffusion of the Cu atoms.The effects of interface structures on the deformation and fracture of Cu/V multilayers are investigated through the state-of-the-art in situ transmission electron microscopy mechanical testing.It shows that the sharp interfaces and ITZs exert different influences on the fracture behavior.Specifically,crack transmits across the layers layer-by-layer where the interfaces possess sharp structure,while microcracks occur between ITZs and Cu lamella,facilitating the fracture.The formation of the microcracks can be attributed to three factors:1)slip discontinuity induced deformation incompatibility;2)weak bonding strength between Cu layers and ITZs,which can be corroborated by the different crack propagation pathway along two kinds of interfaces;3)dislocation-interface interaction near the ITZs,causing the formation of vacancies.These findings are of great significance in understanding the mechanical properties of nanoscale metallic multilayers and shed light on the study of the nonconventional interfaces in all kinds of nanoscale metallic multilayers.