(1. 哈尔滨工业大学 材料科学与工程学院，哈尔滨 150001；
2. 哈尔滨工业大学 微系统与微结构制造教育部重点实验室，哈尔滨 150080；
3. 哈尔滨工业大学 基础与交叉科学研究院，哈尔滨 150080；
4. 哈尔滨工业大学 机电工程学院，哈尔滨 150001)
摘 要: 研究纯镍丝材单向微拉伸塑性变形过程中的流动应力和非均匀变形行为尺寸效应。实验发现，流动应力随晶粒尺寸的增加(或直径方向上晶粒数量的减少)而降低，而非均匀变形程度增加。当直径方向上少于9.3个晶粒时，流动应力随晶粒尺寸增加而快速降低。通过引入晶界尺寸因子构建介观尺度材料本构模型揭示丝材微拉伸流动应力尺寸效应。结果表明，断裂应变和断裂应力随着晶粒尺寸的增加而减小。当试样直径方向上少于14.7个晶粒时，断裂应变和断裂应力快速降低，表明微拉伸过程中的非均匀变形程度随着直径方向上晶粒数量的减小而增加。当试样直径方向上的晶粒数量减少时，断口形貌变得越来越不规则。从材料微观组织分布方面分析了不规则断口形貌的形成机理。
关键字: 镍丝；尺寸效应；微拉伸；流动应力；非均匀变形；断裂
（1. School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China;
2. Key Laboratory of Micro-systems and Micro-structures Manufacturing, Ministry of Education,
Harbin Institute of Technology, Harbin 150080, China;
3. Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080, China;
4. School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China）
Abstract:Size effects on plastic deformation behaviors in uniaxial micro tension of pure nickel fine wires were investigated experimentally, including flow stress and inhomogeneous deformation behaviors. It is found that with the increase of grain size or the decrease of number of grains across the diameter, the flow stress decreases and inhomogeneous deformation degree increases. When there are less than 9.3 grains across the diameter, the flow stress decreases quickly with the increase of grain size. Then, the flow stress size effect in micro tension of fine wires is revealed by a proposed model by introducing the grain boundary size factor. These results also indicate that both the fracture strain and stress decrease with the increase of grain size. When there are less than 14.7 grains across the diameter, both the fracture strain and stress decrease quickly. This indicates that the inhomogeneous deformation degree in micro tension increases with the decrease of the number of grains across the diameter. The fracture topography tends to be more and more irregular with the decrease of the number of grains across the diameter. Then, the formation mechanism of irregular fracture topography was analyzed considering the inhomogeneous distribution of microstructure when there are a few grains across the diameter.
Key words: nickel wire; size effect; micro tension; flow stress; inhomogeneous deformation; fracture
