Hydrogen-induced Material Degradation: Brittle Decohesion Versus Plastic Flow Localization

拟议的工作的主要目标是识别在一个定量的方式负责模型和工业相关的工程材料的氢致降解的基本机制，使用一个完全集成的，结合应用力学/建模和材料科学/微观结构的方法。该方法结合了定量，大规模的数值模拟与新的实验和原位成像，以确定显着的物理微观机制和特征微观结构的尺寸尺度参与局部断裂事件。由于这种断裂事件是随机的，因此分析本质上是统计的，针对真实的微观结构制定并且基于操作物理微观机制。 这项工作的主要成果将是建立基于物理的工程标准，氢相关的断裂韧性和脆性金属材料，氢降解的主要机制，特别是脱粘和剪切局部化，是活跃的。 由于它们的工业重要性，这些材料包括低强度钢和高强度钢以及Ni 3Al高温金属间化合物。 第二个成果将是材料科学的学生培训，但在材料行为的力学分析的背景下。 从事该项目的研究生和本科生将接触材料科学和应用力学文化;因此，他们将获得现代断裂研究人员所需的基本能力。 由于该研究主要集中在真实的工程意义的结构材料上，因此学生们正在以跨学科的方式接受结构工程支柱的教育。%实现这些目标为许多与氢脆相关的紧迫科学问题提供了答案。这些包括（i）脆性脱粘与氢辅助剪切局部化机制的相对重要性，（ii）氢增强局部塑性促进局部断裂的过程，（iii）平衡与非平衡脱粘理论的相关性，以及（iv）溶质杂质在不同材料微观结构中的作用和潜在的协同作用。这项工作还对材料在恶劣环境条件下的一般操作产生了重大的技术影响。 此外，它代表了先进材料（如金属间化合物）在任何环境中成功应用的一种使能技术，因为对这些材料中环境辅助局部断裂事件的标准知之甚少。

The prime objective of the proposed work is to discern in a quantitative fashion the fundamental mechanisms responsible for the hydrogen-induced degradation of both model and industrially-relevant engineering materials using a fully integrated, combined applied mechanics/modeling and materials science/microstructural approach. The approach combines quantitative, large-scale numerical simulations with novel experimentation and in situ imaging to identify the salient physical micro-mechanisms and characteristic microstructural size-scales involved in the local fracture events. Since such fracture events are stochastic, the analysis is statistical in nature, formulated for real microstructures and based on the operative physical micro-mechanisms. The principal outcome of this work will be the establishment of physically based engineering criteria for hydrogen-related fracture in both ductile and brittle metallic materials, where the primary mechanisms of hydrogen degradation, specifically decohesion and shear localization, are active. Because of their industrial significance, these materials include low and ultrahigh strength steels and a Ni3Al high-temperature intermetallic. A second outcome will be the training of students in materials science, but in the context of mechanics-based analyses of material behavior. Graduate and undergraduate students who work on the project are exposed to both the materials science and applied mechanics cultures; thereby, they will acquire an essential capability required of modern researchers in fracture. Since the study focuses largely on structural materials of real engineering significance, students are being educated in an interdisciplinary way on the mainstay of structural engineering.%%%Meeting these goals provides answers to numerous pressing scientific issues associated with hydrogen embrittlement. These include (i) the relative significance of brittle decohesion versus hydrogen-assisted shear localization mechanisms, (ii) the process by which hydrogen enhanced localized plasticity promotes localized fracture, (iii) the relevance of equilibrium vs. non-equilibrium decohesion theories, and (iv) the role, and potential synergism, of solute impurities in varying material microstructures. The work also has a significant technological impact on the general operation of materials under severe environmental conditions. Moreover, it represents an enabling technology for the successful application of advanced materials such as intermetallics in any environment, since so little is known about the criteria for environmentally assisted local fracture events in these materials.