金属材料氢致断裂行为及其位错动力学机理的多尺度研究

As the smallest atom in nature, hydrogen can enter the interior of the material easily and be trapped by defects such as dislocations and grain boundaries or be adsorbed by the inner and outer surfaces, resulting in a significant decrease in the mechanical properties of the material, causing sudden breakage. Hydrogen-induced fracture of materials involves both hydrogen diffusion, trapping and transport, as well as complex physical processes such as hydrogen enhanced localized plasticity, adsorption induced dislocation emission, and hydrogen enhanced decohesion. It is the cross frontier of solid mechanics and materials science, which has important research significance and potential engineering application prospects. This project intends to carry out in-depth and systematic research on the hydrogen-induced fracture process and its physical mechanism in metals through the combination of microscopic experiments, theoretical analysis and multi-scale simulation. Firstly, it reveals the effects of hydrogen on long-range and short-range interaction to dislocations. Hydrogen induced crack tip dislocation emission and hydrogen induced crack debonding expansion mechanism are further studied to develop the discrete dislocation evolution model, dislocation emission model and crack debonding propagation model affected by hydrogen. Then, based on extended finite element method, the coupling dynamics algorithm and program simulating crack propagation and discrete dislocation evolution is developped. On this basis, hydrogen induced fracture processes in several typical metal are simulated, the model, algorithm and program are verified, and the hydrogen induced fracture mechanism of the material under different conditions is revealed. The research of this project will provide theoretical and technical support for the analysis of hydrogen-induced fracture behavior, which is a common problem in engineering applications.

作为自然界最小的原子，氢极易进入材料内部被位错、晶界等缺陷捕捉，也易被内外表面吸附，导致材料力学性能显著降低，引起突发性断裂。材料氢致断裂问题既涉及氢的扩散、捕捉和输运，也涉及氢致塑性变形、裂尖位错发射、裂纹扩展等复杂物理过程，是固体力学与材料学的交叉前沿，具有重要研究意义和潜在工程应用前景。本项目拟通过微细观实验、理论分析和多尺度模拟等方法的有机结合，对金属氢致断裂过程及其物理机理开展深入、系统的研究：首先，揭示氢对位错间长程及短程作用、氢致裂尖位错发射、氢致裂纹脱粘扩展的机理，发展受氢影响的离散位错演化、位错发射和裂纹脱粘开裂模型；然后，基于扩展有限元方法，发展模拟裂纹扩展和离散位错演化的耦合动力学算法及程序；在此基础上，对几种典型金属氢致断裂过程进行模拟，验证模型、算法和程序，并揭示材料在不同条件下的氢致断裂机理。本项目的研究，将为工程中常见的氢致断裂行为的分析提供理论和技术支撑。

金属材料的氢脆失效发生在腐蚀的极端服役环境，严重威胁材料及结构的安全，是国民经济和国防工业中常见的关键科学问题，制约着我国在相关领域的技术进步。同时，它又涉及“环境断裂过程中多维缺陷间复杂的相互作用”这一力学和材料、物理的交叉前沿问题，具有重要的学术价值和深远的科学意义。本项目以 “材料氢致断裂行为及其内在变形机理的定量表征”这一关键基础科学问题为导向，通过微细观试验结合理论分析与多尺度模拟研究，揭示了氢致断裂过程的位错机理，并建立了氢环境下材料内部微缺陷演化与宏观断裂行为间的内在关联。首先，在微观尺度上采用分子动力学模拟，深入研究了氢与材料内部多维缺陷（空位、位错、晶界、裂纹）间的相互作用规律并提炼了相应的定量表征模型，为“升尺度”模拟提供了底层原子尺度的力学信息；其次，在细观缺陷尺度上，建立了基于扩展有限元的界面断裂行为离散位错动力学算法框架，通过融入氢的扩散动力学模块与多维缺陷相互作用介观模型，搭建了氢致断裂行为的离散位错动力学模拟程序，实现了氢致断裂过程中多种氢脆机制的协同作用研究；最后，为了深入揭示金属氢致断裂行为中材料内部缺陷演化过程的影响，通过开展多晶纯镍含氢试样的介观尺度离散位错模拟及低应变率下的微拉伸实验并结合SEM、EBSD、XRD等表征分析，详细揭示了以晶粒尺寸为代表的晶体微结构及以初始位错密度为代表的缺陷微结构对氢致断裂行为的影响及其作用机理，同时进一步验证了本项目发展的氢致断裂行为离散位错动力学模拟算法及程序的准确性。上述研究成果揭示了氢致材料断裂的细观过程及位错机理，丰富了人们对氢致断裂现象的认识。同时，不仅对“升尺度”构建晶体塑性有限元本构模型奠定了基础，还可以为不同晶体结构下金属材料的氢脆防护及改良设计提供物理基础和理论依据。