【作者】 朱晓莹；

【导师】 潘峰；

【作者基本信息】 清华大学 ， 材料科学与工程， 2010， 博士

【摘要】 近年来,新型功能材料及器件向小型化,集成化和复合化发展的趋势,使得尺寸在纳米尺度的层状材料和柔性多层器件在使用过程中的服役行为成为其发展的关键科学问题。本文采用超高真空电子束蒸发镀膜工艺制备了fcc/fcc体系Cu/Ni和Cu/Co纳米多层膜及fcc/bcc体系Cu/Nb和Ag/Fe纳米多层膜,研究了纳米多层膜力学性能与其微结构,尤其是界面结构之间的关系,探讨了纳米多层膜在不同尺度范围的塑性变形机制。研究结果表明,具有完全共格界面的Cu/Ni和Cu/Co纳米多层膜的强度值与其共格界面上的共格应力相等,在实验上证实了共格应力是决定fcc/fcc超晶格结构纳米多层膜强度最大值的关键因素。Cu/Nb纳米多层膜的强度最大值为3.27GPa,是Cu/Nb纳米多层膜强度平均值的2.1倍,表现出很大的强化效应。此外,变加载应变率硬度实验证明Cu/Nb纳米多层膜的超高强度与大的应变硬化有关。论文中所研究的金属纳米多层膜的强度(或硬度)在周期变化范围内均随周期的减小而增大,表现出强化效应。Cu/Ni、Cu/Co和Cu/Nb纳米多层膜在大周期时的塑性变形机制为单个位错在层内滑移机制;在小周期时,塑性变形机制转变为位错穿越界面机制。Ag/Fe纳米多层膜的硬度随周期的变化符合类Hall-Petch关系。论文中所研究的金属纳米多层膜的弹性模量在周期变化范围内均超过了弹性模量平均值,表现出弹性模量增强。Cu/Nb纳米多层膜的弹性模量比弹性模量平均值最大增加38%,不对称的界面结构是导致Cu/Nb纳米多层膜出现异常弹性模量增大的主要原因。对fcc/fcc超晶格结构Cu/Ni和Cu/Co纳米多层膜来说,弹性模量增强与半共格界面的界面压应力以及共格界面的共格应力相关。界面压应力是Ag/Fe纳米多层膜的弹性模量在小周期增大的主要原因。本论文所研究的金属纳米多层膜的室温蠕变机制都是位错滑移-攀移机制。非共格界面为位错的攀移运动提供了有效的扩散通道,Cu/Nb和Ag/Fe多层膜的蠕变抗力随周期减小而减小。相反,共格界面的形成不利于位错的攀移运动,Cu/Ni和Cu/Co多层膜的蠕变抗力随周期减小而增大。提出的基于位错在半共格界面上增殖和回复的动态平衡位错模型能合理地解释在大周期具有半共格界面的Cu/Ni和Cu/Co纳米多层膜的稳态室温蠕变过程。更多还原

【Abstract】 Recently, the tendency of new functional materials and devices to being miniature, integrated and laminated makes the mechanical behavior of those materials in nano scale a key scientific issue for the development of the multilayers and devices. In the dissertation, the fcc/fcc system of Cu/Ni and Cu/Co multilayers and fcc/bcc system of Cu/Nb and Ag/Fe multilayers were prepared via electron beam evaporation deposition in high cacuum and the relationship between mechanical properties and microstructure, specially for the detailed structure of the interfaces, are discussed, and the plastic deformation mechanism in different length-scale regime is explored.The results show that for fcc/fcc Cu/Ni and Cu/Co metallic multilayers with fully coherent interfaces, the peak strength equals to coherent stress. It verifies in experiment that the peak strength that can be achieved in fcc/fcc superlattice is mainly determined by conherent stress. The peak strength of the fcc/bcc Cu/Nb metallic multilayers is 3.27GPa, which is consistent with the theoretical value predicted by atomic modeling based on dislocation transmission through interfaces. Meanwhile, varying loading strain rate hardness measurement confirms that the ultrahigh strength of nanoscale Cu/Nb multilayers is partly due to large strain strengthening.The strength (or hardness) of all the investigated multilayers increases with decreasing periodicity. For Cu/Ni, Cu/Co and Cu/Nb multilayers, the plastic deformation follows the confined layer slip model at large periodicity, while it changes to the mechanism of dislocation transmission through interfaces at small periodicity. For Ag/Fe multilayers, the variation in hardness with decreasing periodicity obeys the Hall-Petch-like relationship.There is modulus enhancement of all the investigated multilayers compared with the rule of mixing value. For Cu/Nb multilayers, solid solution of Cu in Nb interfaces caused by asymmetrical growth dynamics leads to 38% modulus enhancement. For fcc/fcc superlattice of Cu/Ni and Cu/Co multilayers, the modulus enhancement is related to compressive interface stress in semi-coherent interfaces or coherent stress in coherent interfaces. While for fcc/bcc Ag/Fe multilayers, the slight modulus enhancement at small periodicity is ascribed to compressive interface stress. The creep process of all the investigated multilayers is dominated by dislocation glide-climb mechanism. For fcc/bcc Cu/Nb and Ag/Fe multilayers, the incoherent interfaces can provide effective climb diffusion paths and thus the creep resistance decreases with decreasing periodicity. On the other hand, the formation of coherent interfaces is disadvantageous to the dislocation climb process and creep resistance of Cu/Ni and Cu/Co multilayers increases with decreasing periodicity. A dislocation model based on dislocation generation and annihilation at semi-coherent interfaces is presented to predict the steady-state deformation of Cu/Ni and Cu/Co multilayers with large periodicity and model predictons agree well with experimental observation.更多还原