单晶铝的负应变速率敏感性  

The negative strain rate sensitivity in single crystalline Al

作　　者：黄龙超 孙妮娜 王章洁 单智伟[1] HUANG Long-chao;SUN Ni-na;WANG Zhang-jie;SHAN Zhi-wei(Center for Advancing Materials Performance from the Nanoscale(CAMP-Nano),State Key Laboratory for Mechanical Behavior of Materials,School of Materials Science and Engineering,Xi'an Jiaotong University,Xi'an Shaanxi 710049,China)

机构地区：[1]西安交通大学材料科学与工程学院,金属材料强度国家重点实验室,微纳尺度材料行为研究中心,陕西西安710049

出　　处：《电子显微学报》2021年第5期550-557,共8页Journal of Chinese Electron Microscopy Society

基　　金：国家重点研发项目(No.2017YFB0702001);国家自然科学基金资助项目(No.51971167);西安市科技计划项目(No.2017xasjl014)。

摘　　要：面心立方金属通常具有较弱的正应变速率敏感性,即流变应力随着应变速率的增加而增加。近年的研究表明,随着晶粒尺寸或单晶样品尺寸减小到微纳米尺度,其正应变速率敏感性显著增加。然而,通过位移速率控制条件下压缩测试,作者发现当单晶铝柱的直径<190 nm左右时,其呈现出反常的负应变率敏感性。分析表明,这一现象的产生是由于在较低应变率下,铝柱内产生的位错容易从表面逃逸,其后续塑性变形由位错表面形核机制主导,流变应力较高;而在较高应变率下,铝柱内产生的位错在从表面逃逸前已发生交互作用,其塑性变形由内部位错增殖机制主导,因而流变应力相对较低。上述发现丰富了人们关于几何尺寸降低对金属加载速率响应行为的认知。The face-centered cubic metals usually have a very low positive strain rate sensitivity,that is,the flow stress improves slightly as the strain rate increases.Studies in recent decades have demonstrated that as the grain size or sample size reduces to micro-and nanoscale,their strain rate sensitivity significantly increases.However,through displacement-rate-controlled compression tests,we find an abnormal negative strain rate sensitivity of pillars with diameters less than~190 nm.Such negative strain rate sensitivity arises from the transition of the rate-controlling deformation mechanisms as the strain rate varies.Upon lower strain rate,dislocations inside these Al pillars can easily escape from the free surface,leading to a thorough mechanical annealing and dislocation starvation,therefore the subsequent plastic deformation is dominated by surface dislocation nucleation,showing higher level flow stress.While upon higher strain rate,dislocations inside Al pillars shall interact with each other before they completely escape from the surface,hence the plastic deformation is controlled by internal dislocation multiplication instead,exhibiting much lower level flow stress.These findings help to enrich people’s understanding of the strain rate-dependence of the mechanical responses as the sample size reduces.

关 键 词：单晶铝 微纳尺度 应变速率敏感性 位错形核与增殖 

分 类 号：TG146.21[一般工业技术—材料科学与工程] TG115.53[金属学及工艺—金属材料]