Cu/Nb纳米金属多层膜延性及断裂行为的尺寸效应

LENGTH SCALE DEPENDENT DUCTILITY AND FRACTURE BEHAVIOR OF Cu/Nb NANOSTRUCTURED METALLIC MULTILAYERS

通过单轴拉伸实验并结合原位电阻测量法系统研究了恒定调制比下调制波长(λ=10—250 nm)对聚酰亚胺基体上Cu/Nb纳米金属多层膜延性和断裂韧性的影响.微观分析表明,Cu/Nb的调制结构清晰,不存在明显的互混现象.实验结果表明,随着调制波长的减小,多层膜的延性和断裂韧性均呈现非单调演变趋势,在调制波长为50 nm左右出现峰值.这是由于随着层厚的变化,脆性Nb层内起始微裂纹扩展能力和延性Cu层抑制裂纹扩展能力这两个因素之间的相互竞争关系变化引起的.采用断裂力学理论对这种竞争关系及其引起的延性和断裂韧性非单调变化趋势进行了定性分析.

By using uniaxial tensile test combining the in situ electrical resistance change method, the influence of modulation period with a wide range spanning from 10 to 250 nm on the ductility and fracture toughness of Cu/Nb nanostructured metallic multilayers on polyimide substrate was measured. The microstructural analysis revealed that the modulation structure of Cu/Nb metallic multilayers was clear and no intermixing between Cu and Nb was been found by using line scanning analysis. The experimental results indicated that both ductility and fracture toughness of the multilayer film exhibited a nonmonotonic change with decreasing modulation period, and reached maximum values at a critical modulation period of about 50 nm. This was attributed to the competing effect between the size of the microcracks initiated in the Nb layer and the role of the Cu layer in blocking crack propagation. This competing effect was qualitatively assessed on basis of fracture mechanics.