CAREER: Identifying the Micromechanisms Leading to Hydrogen-Induced Intergranular Fracture in Metals

这个学院早期职业发展（Career）项目将确定镍（Ni）及其合金在耦合环境和机械条件下的潜在变形和破坏机制。镍和镍基合金由于其高强度和断裂韧性，通常用于许多关键的服务应用。在许多情况下，这些材料用于能源产生、转换或储存系统。在这种条件下，与氢接触有关的韧性损失可能发生。该奖项支持氢对金属变形和断裂影响的基础研究，并将通过能源系统结构完整性的进步为工程实践做出贡献。通过这项拨款的教育和推广任务将有助于提高巴尔的摩少数民族学生人数较多的小学公立学校的STEM成绩。实际工程问题和解决方案将在课堂上提出和讨论，目的是激发对工程的兴趣。来自当地一所历史悠久的黑人大学的本科生将获得研究实习机会，允许他们积极参与这个CAREER研究项目。这将使学生对材料力学的职业发展产生兴趣和基础。本CAREER项目的主要研究目标是从根本上确定h扩散对Ni晶体位错微观结构演化、损伤积累以及随后h致晶间断裂的影响。我们假设，与传统的假设不同，位错塑性在控制材料响应和随后的破坏中起着重要作用，即使在高压H环境中也是如此。我们将进行前所未有的大规模三维离散位错动力学（DDD）模拟，并结合有限元方法来研究含氢单晶、双晶和多晶中的位错演化。位错-氢相互作用、位错晶界相互作用和氢管/体扩散的细节将通过分子动力学（MD）模拟来确定，然后分层地通知到DDD。特别是，这项工作将解决两个基本问题：(1)H如何影响位错的增殖/演化？(2) h扩散对位错微观结构的演化有何影响？MD模拟将：(1)量化H对交叉滑移激活参数的影响；(2)量化h扩散系数和位错晶界相互作用。耦合H扩散/DDD模拟将用于确定H浓度和晶粒尺寸对：(1)流动强度和滑移形貌的影响；(2)位错演化先于h致晶间裂纹。模拟将通过与文献中关键实验结果的比较来验证。

This Faculty Early Career Development (CAREER) Program project will identify the underlying deformation and failure mechanisms of nickel (Ni) and its alloys under coupled environmental and mechanical conditions. Nickel and nickel-based alloys are commonly used in many crucial service applications due to their high strength and fracture toughness. In many cases these materials are used in energy generating, conversion or storage systems. In such conditions a loss of toughness associated with exposure to hydrogen can occur. This award supports fundamental research on the effect of hydrogen on the deformation and fracture of metals, and will contribute to engineering practice via advances in the structural integrity of energy systems. The education and outreach tasks through this grant will contribute to efforts aiming to improve STEM achievement in Baltimore elementary public schools with a high minority student population. Practical engineering problems and solutions will be presented and discussed in the classroom with the goal to stimulate interest in engineering. Undergraduates from a local historically black college will obtain research internships allowing for active involvement in this CAREER research project. This will allow students to develop interest and foundations for careers in mechanics of materials. The primary research objectives of this CAREER project are to fundamentally identify the influence of H-diffusion on dislocation microstructure evolution, damage accumulation, and subsequent H-induced intergranular fracture of Ni crystals. We hypothesize that, unlike conventionally presumed, dislocation plasticity plays a major role in controlling material response and subsequent failure even in high-pressure H environments. We will perform unprecedented large scale 3D discrete dislocation dynamics (DDD) simulations coupled with finite element method to study dislocation evolution in H-charged single, bi, and poly-crystals. Details of the dislocation-H interactions, dislocation grain boundary interactions, and H pipe/bulk diffusion will be identified through molecular dynamics (MD) simulations, then hierarchically informed into DDD. In particular, this work will address two fundamental questions: (1) How does H influence dislocation multiplication/evolution? and (2) What is the role of H-diffusion on the evolution of the dislocation microstructure? The MD simulations will: (1) quantify H effects on the activation parameters of cross-slip; and (2) quantify H-diffusion coefficients and dislocation grain boundary interactions. Coupled H-diffusion/DDD simulations will be used to identify effects of H concentration and grain size on: (1) flow strength, and slip-morphology; and (2) dislocation evolution ahead of H-induced intergranular cracks. Simulations will be validated by comparisons with key experimental results from literature.