Defect mediated plasticity in Cu/Ag nanoscale multilayered metal composites: deformation twinning and wavy interface formation

Nanolayered metals;flaws;deformation twinning;interface migration;wavy interfaces;molecular dynamics

Li, Ruizhi ; Chew ; Huck Beng

关键词: Nanolayered metals;    flaws;    deformation twinning;    interface migration;    wavy interfaces;    molecular dynamics;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/45307/Ruizhi_Li.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The exceptional mechanical properties of metallic nanolayers originate from the high density ofnanoscale interfaces. However, conflicting observations in the relationship between mechanicalproperties and interlayer thicknesses, as well as discrepancies in measured strength betweenexperiments and simulations, suggest that microstructural flaws play an essential role in thedeformation behavior of actual metallic nanolayers. In this thesis, molecular dynamicssimulations are used to uncover two distinct nanoscale plasticity mechanisms activated by thepresence of micro-cracks and columnar grain boundaries in Cu/Ag nanolayers under tension. Thefirst mechanism is deformation twinning, caused by emission of twinning partials from themicro-cracks and columnar grain boundaries. These deformation microtwins are transmittedacross multiple Cu/Ag interlayers and facilitate the communication between spatially separatedflaws. In addition, the intersections of microtwins on non-parallel slip planes produce formidablelocks, which serve as stress concentration sites for incipient crack growth. The secondmechanism is interlayer interface migration, which results in the morphological transition ofinitially planar Cu/Ag nanolayer to become wavy. This planar-to-wavy transition is driven byenergetics, and is facilitated by dislocation climb along columnar grain boundaries. The abovetensile-activated plasticity mechanisms are distinctly different from the strengthening mechanismassociated with interface crossings of single dislocations under compression. Implications ofthese mechanisms to the ductility of metallic nanolayers, as well as the activation of novelnanoscale plastic recovery processes, are discussed.