力热耦合作用下大塑性变形纳米材料的变形行为

Nanocrystalline materials fabricated using severe plastic deformation method is one of potential structural materials in various engineering fields. Since the mechanical properties of nanocrystalline materials are influenced by both temperature and strain rate, investigations on their deformation behaviors under mechanical and thermal loads are of great importance in both scientific and engineering aspects. However, our current knowledge about these is still limited. In this project, by using experimental measurements, microstructural observation and theoretical analysis methods, we aim to investigate the deformation behaviors of nanocrystalline materials with face center cubic structure sysmetically. Based on uniaxial compressive experimental results and microstructural observations, the temperature and strain rate sensitivities of the material will be determined. The inner relationship between its deformation behaviors and mechanical-thermal coupling conditions will be also explored. Finally, a physical model will be proposed to describe the dependence of strain rate and temperature sensitivities of nanocrystalline material with face center cubic structure on microstructural characterizations. The research achievements of this project will be of great scientific meaning for our full understand the deformation mechanism of nanocrystalline materials.

大塑性变形纳米材料是工程领域具有广泛应用前景的结构材料之一，其力学行为受到温度和应变率的耦合影响。然而，目前对宽温度、宽变率范围内纳米材料变形行为的认识还很不全面，亟需开展力热耦合作用下纳米材料塑性变形规律相关的研究工作。本项目拟采用实验测试、微观组织观察和理论分析相结合的研究手段，通过宽温度、宽变率范围内纳米材料的力学性能实验及微观组织观察，研究其塑性变形行为的温度、应变率敏感性及依赖性，揭示材料的塑性变形行为与力热耦合条件的关联性；并基于热激活理论，构建可描述面心立方大塑性变形纳米材料的温度、应变率敏感性与微观组织关系的物理模型。研究结果不仅对于全面认识和掌握纳米材料的力学行为具有重要的科学意义，而且对其在工程结构应用中的安全性设计具有指导作用。

大塑性变形纳米材料是工程领域具有广泛应用前景的结构材料之一，其力学行为受到温度和应变率的耦合影响。然而，目前对宽温度、宽变率范围内纳米材料变形行为的认识还很不全面，亟需开展力热耦合作用下纳米结构材料塑性变形规律相关的研究工作。本项目采用等径通道挤压方法对不同铝含量的退火态铜铝合金进行挤压，制备了晶粒尺寸90~350nm的三种纳米结构、超细晶铜铝合金，并分别对三种材料在准静态和动态载荷下进行了单轴压缩实验。研究结果表明，铝含量越大，经过等径通道挤压后材料的晶粒越小；由于材料制备过程中经历了大塑性变形，单轴压缩时材料的加工硬化能力，几乎完全丧失，铝含量为11.14%的纳米结构铜铝合金甚至在高应变率下出现应变软化。对变形前后以及绝热剪切带内的材料微观组织观察表明，随着铝含量的增加，材料的塑性变形机制由位错运动向以孪生变形为主转变。利用光学显微镜和扫描电镜对铝含量为11.14%的纳米结构铜铝合金动态变形后试样进行观察发现，该材料的应变软化与绝热剪切带的形成有关，这是目前为止首次在面心立方金属单轴压缩变形时观察到绝热剪切带。为了进一步认识绝热剪切带的形成机理，采用聚焦离子束切割的方法在绝热剪切带内部、周围分别制备出透射电镜样品，观察表明11.14%铝含量纳米铜铝合金动态变形时绝热剪切带的形成与动态再结晶有关。