金属材料复杂服役条件下三维多尺度应力场演化与损伤机制关联性研究

The main objective of this project is intended to explore a critical scientific issue on the relationship between the deformation damage mechanisms and the microstructure evolution mainly controlled by change in three-dimensional (3D) multi-scale stress distribution under complex stress and temperature fields for high-strength aluminum alloys, single crystal superalloys, zirconium alloys and stainless steels widely used as important aircraft and nuclear engineering components. Based on the neutron scattering technique, in combination with other advanced in-situ characterization methods such as the synchrotron-based X-ray diffraction, it is predicted that some breakthroughs will be achieved through a successful execution of this program in the following four aspects: (1) New experimental methods will be established for in-situ characterizing the microstructure evolution with the temporal and spatial resolution and the accompanied change in multi-scale stress fields; (2) The evolution of 3D multi-scale microstructural unit, including volume fraction and distribution of phases, micro-stress/strain, grain orientation, and nano-/ micro- scale cracks/ voids will be investigated for the above-mentioned single- or multi-phase materials subjected to complex stress and temperature environments, such as low/high cycle fatigue, creep and thermal-mechanical fatigue; (3) Based on the direct measurements of lattice strain distributions obtained by in-situ neutron scattering and synchrotron-based X-ray diffraction experiments, an integrated framework for multi-scale simulations across different length scales using the finite element, self-consistent, molecular dynamics, and linear-scaling quantum mechanical method will be performed on modeling the micro-mechanical behavior and formation of cracks in anisotropic polycrystalline materials; and (4) A new microstructure-based damage theory that can accurately predict the service performance and deformation damage of anisotropic polycrystalline materials under the complex service conditions will be developed. The successful execution of this program will also provide a significant experimental and theoretical basis for further improving the service security and accurately predicting the service life of some important materials and engineering components.

本项目拟围绕"复杂应力和温度作用下三维多尺度应力分布变化主导的微结构演化与形变损伤行为的关联性"这一关键科学问题，以高强铝合金、单晶高温合金、锆合金和不锈钢等航空或核工业用重要工程部件材料为研究对象，主要采用中子散射技术并结合同步辐射等先进手段，建立时空分辨的微观结构/多尺度应力场的原位表征与测量新方法；研究在复杂应力与温度作用（低/高周疲劳、蠕变及热机械疲劳）下，单/多相材料三维多尺度微观结构单元（相体积分布、微应力/应变、晶粒取向、纳/微米尺度裂纹/孔洞）的演化规律；有效结合中子散射等方法原位测得的实验数据，开展多尺度各向异性材料微观力学行为的跨尺度（有限元、自洽、分子动力学与大尺度线性标度的第一性原理）模拟研究；发展基于微观组织控制为基础的，能对材料在复杂服役条件下使役行为进行精确预测的变形损伤微观新理论。研究结果将为进一步提高材料部件的服役安全性和使用寿命提供重要的实验和理论基础。

本项目利用中子衍射与同步辐射高能／微束衍射技术，以航空、核工业领域重要工程材料为研究对象，以“复杂应力、温度作用环境下三维多尺度应力分布主导的微结构演化与形变损伤行为的关联性”这一科学问题研究为主线：（1）建立了应力、温度环境下三维空间多尺度应力场原位测量的先进方法与实验装置，该方法与技术不仅适用于工程材料的损伤研究，而且实现了大型工程部件多尺度应力测量；（2）研究典型立方与六方金属材料（奥氏体不锈钢、TWIP钢、核工业用Zr合金、纯Ti等）在应力、温度及循环加载等复杂服役条件下的多尺度应力演化与微观变形机制，成功揭示形变过程中孪晶／相变导致的局域大应变梯度与微观损伤破坏的关联。发现Zr-4合金吸氢生成的δ氢化物在形变过程中转变成具有HCP结构的ζ-Zr2H氢化物，其与α-Zr基体具有“hexagon-on-hexagon”的特定取向关系，有助于理解氢化物延迟开裂现象；（3）建立了多尺度各向异性有限元/自洽模型，并通过与中子/同步辐射实验测量数据比较，获取微观力学模拟所需准确的材料参量，准确预测材料的微观力学行为与损伤。项目取得的重要结果：基于同步辐射X射线微束技术，首次表征了疲劳剪切带位错结构引起的巨大应力梯度与微小取向梯度，成功解决一直众说纷纭并长期困扰着材料科学家的剪切带交互作用导致微观损伤的物理机制；清晰阐明了平面滑移金属低应变幅循环形变时，疲劳寿命偏离经典Coffin-Manson的普适规律，并建立了疲劳局域损伤新的位错动态演化模型。该研究成果发表于PNAS，对金属材料的疲劳断裂行为与使用寿命准确预估及高性能设计具有重要指导意义，项目负责人应邀参加第十八届材料织构大会，代表中国作40分钟的大会报告。项目的基础成果已在SCI期刊发表88篇学术论文，其中包括《PNAS》1篇，《Nature communications》1篇，《Acta Materialia》11篇，《Scientific Reports》2篇，以上论文SCI总引用达446次。面向我国航空发动机研发与生产的迫切需求，利用项目实施中发展的装置／技术开展了航空用重要工程部件三维应力场的测量与评估，直接服务于我国航空工业。