几种金属多层薄膜的形变与断裂行为及其机制

Deformation and fracture behavior of several metallic multilayers and mechanisms

本文系统地报道了近年来所开展的有关金属多层薄膜的强度、变形与断裂行为的研究进展.着重介绍了本研究所开展的几种典型金属多层薄膜(Cu/Au、Cu/Cr、Cu/Ta等)的力学行为及其尺寸与界面效应.研究发现,随着多层膜的单层厚度减小,多层膜的强度明显升高,最后达到饱和.理论分析表明,不同种类金属多层膜的强度升高能力与界面结构有关.根据晶格失配与位错理论,所提出的统一模型可以很好地描述具有不同界面结构金属多层薄膜的界面强化能力.压痕诱发的具有不同尺度和界面结构的金属多层膜的塑性变形行为明显不同.当多层膜的单层厚度减小到纳米尺度时,压痕诱发的塑性变形倾向于剪切带变形;同时还在亚微米尺度下观察到了直接穿过界面的局部剪切行为.研究还发现,在单向拉伸载荷的作用下,纳米尺度Cu/Ta多层膜的裂纹尖端发生位移量为几纳米到几十纳米的面外剪切变形,最终导致Cu/Ta多层膜发生剪切型断裂.提出了位错运动所需应力和层/层界面阻力之间的竞争机制,从而证明了当金属多层膜的单层厚度小于某一临界尺度时将发生剪切型断裂这一物理本质.

Recent research progresses in strength, deformation and fracture behavior of metallic multilayers have been systematically reported in this paper, with the emphasis on our work on the mechanical behavior and the effects of length scale and interface structure of several typical metallic multilayers （Cu/Au, Cu/Cr, Cu/Ta etc. ）. It is found that the strength of the metallic muhilayers is enhanced with the decrease in individual layer thickness, and fi- nally saturates at a critical length scale. Theoretical analysis reveals the dependence of strengthening ability in various metallic muhilayers on the interface structure. Based on the lattice mismatch and dislocation theory, a unified model proposed by us gives a good description of the interface strengthening ability of the metallic multilayers with different interface structures. Indentation-induced plastic deformation behavior of the metallic multilayers with dif- ferent length scales and interface structures is evidently different. When the individual layer thickness is reduced to nanometer-scale, the metallic muhilayer under indentation is prone to lose plastic stability via shear banding~ mean- while, localized shearing across the interface is also observed in the submicron-scale. Besides, we observed that the shear displacement in a range from several nanometers to a few tens of nanometers occurring in the plastic deforma- tion zone ahead of a crack tip in Cu/Ta multilayer subjected to monotonic tensile load. As a result, shear-mode frac- ture of the Cu/Ta multilayer was caused eventually. The comparison of the interface barrier strength of the multilay- er with the applied shear stress of dislocation gliding in the confined layer finds a critical individual layer thickness below which the nature of fracture of the metallic multilayer tends to be shearing failure.