块体纳米金属循环变形行为的微观机理及晶体相场模型研究

Nanocrystalline metals and alloys are increasingly found to have improved mechanical properties over their coarse-grained counterparts, such as high yield and fracture strength, hardness, excellent friction, wear and high cycle fatigue resistance, and have broad engineering application prospect. In this project, the uniaxial strain-controlled cyclic deformation behavior and corresponding microscopic mechanisms of bulk nanocrystalline metals with different crystal structures will be investigated by macroscopic and microscopic experiments. The effect of crystal structures, temperature, loading level and loading history on the cyclic deformation behavior and evolution of microstructures will be systematic studied. Then, based on the microscopic analysis, by introducing the reasonable order-parameters which can reflect the microstructures evolution during cyclic deformation, the phase field crystal dynamic model of nanocrystalline metals will be established to simulate and predict the cyclic deformation and microstructures evolution. The reasonability of the proposed phase field crystal model will be verified by comparing with the corresponding macroscopic and microscopic experimental results. This study of this project focus on the key issue of nanocrystalline metals, the reveal of the cyclic deformation mechanisms is meaningful for deeply understanding the deformation mechanism of bulk nanocrystalline metals, and guide for the microstructural design to obtain the elevated comprehensive mechanical properties. Furthermore, the establish of the phase field crystal dynamic model will also give significant theoretical supports for the structural design, safety assessment and fatigue life prediction of nanocrystalline metals and alloys components.

纳米金属材料具有高的屈服和断裂强度、硬度以及优异的耐摩擦磨损和抗高周疲劳特性等力学性能，具有广阔的应用前景。本项目拟对块体纳米金属的循环变形行为进行系统的宏微观实验研究，研究晶格结构、温度、加载水平和加载历史等因素对材料循环变形特性的影响，揭示其循环变形的微观机理。在微观实验研究的基础上，引入合理的序参量来描述循环变形过程中的微结构演化，建立纳米金属循环变形的晶体相场动力学模型，对纳米金属的循环变形响应和微结构演化进行模拟，并通过和宏微观实验结果的对比验证模型的合理性。研究成果对于揭示纳米金属材料循环变形的微观机理具有重要的理论意义，有助于通过结构设计来改善纳米金属材料的综合力学性能；同时，晶体相场动力学模型的建立可为未来纳米金属构件的结构设计、安全评估和寿命预测提供理论支持。

金属材料循环变形的微观机理和理论研究对于工程结构设计和疲劳寿命预测有非常重要的研究意义。本项目开展了对两种金属材料的宏观循环变形实验、微观机理和循环本构模型建模的研究工作。实验研究中，通过位错组态的透射电子显微观察考虑了加载水平和晶格结构对材料循环变形性能和微观机理的影响，得到了材料循环变形行为的微观机理。进而，本项目分别在统一黏塑性框架和晶体塑性框架下建立了可以合理反映两种材料循环变形行为的循环棘轮本构模型：在统一黏塑性框架下，考虑了循环加载过程中的塑性应变记忆效应对于材料循环棘轮响应的影响，提高了该本构模型对循环棘轮行为的预测能力；晶体塑性框架下，考虑塑性变形的位错机制，通过引入可以合理反应材料棘轮效应的修正的Armstrong-Frederick随动硬化演化率和与滑移系流动应力相关的各向同性硬化率，建立了一个新的可以在晶内和晶间尺度上合理预测材料循环变形行为的本构模型。研究成果对于揭示金属材料循环变形微观机理具有一定的理论意义，相关本构模型的搭建对于未来纳米金属构件的结构设计、安全评估和寿命预测提供理论支持。