CAREER: Influence of Grain Boundary Character on the Crack Tip Kinetics of Nickel and Nickel Alloys

技术概述：对提高热效率的需求，从而降低能源消耗，正在推动使用具有更高温度能力的材料，用于各种应用，如陆基动力系统和飞机发动机。在正常操作期间，这些材料在持续的时间内受到环境和热机械的极端影响。在循环加载和停留期间，工作条件处于几种与时间相关的损伤机制（如蠕变变形、氧气扩散和裂纹尖端氧化）的状态。因此，必须充分了解控制随时间变化的损伤和退化的基本机制。在高温蠕变疲劳加载过程中，多晶镍基高温合金由于氧脆而表现出晶间破坏。控制晶界特征分布（GBCD）可以影响裂纹扩展速率，但对裂纹尖端动力学的实际影响尚不清楚。本研究的主要目的是评估镍和镍合金在高温蠕变-疲劳循环过程中晶界特征分布对裂纹尖端动力学（即蠕变变形速率、裂纹扩展速率和沿晶界的氧扩散速率）的影响。裂纹尖端动力学控制裂纹扩展速度，因此如果动力学可以定量描述为温度、保温时间和GBCD的函数，那么这些方面可以纳入寿命预测模型。非技术总结：该项目的目的是确定不同数量的冷加工对镍和镍基高温合金的高温疲劳裂纹扩展行为的影响，并提供一个扩展计划，将通过交互式探究为基础的方法到达多个学校和年级。镍是一些最先进合金的主要合金元素，这些合金用于要求苛刻的应用，如陆基电力系统、飞机发动机和化学加工设备，这些部件在暴露于高温和循环载荷下时需要长期保持机械性能。了解高温工况下的疲劳行为对于预测部件性能至关重要。S长期表现。本项目提出的研究将以多种方式与教育活动相结合，并适用于从K-12到研究生培训的大范围教育水平。K-12教育推广的核心部分将是PI正在开发的一个名为“金属疯狂”的项目。“金属疯狂”计划将在中学课堂上进行，并将提供适合年龄的基本课程，介绍金属是什么以及它们的行为。该计划的最初目标受众将是阿拉巴马州北部地区的中学，这些地区的学生主要由代表性不足的群体组成。本项目的成果将在教育研究生和本科生、教师、高中生和中学生的同时，增加对高温疲劳的认识。研究结果还有望通过提高飞机发动机和陆基发电系统等能源生产部件的预测能力，改善公共安全和福祉。

TECHNICAL SUMMARY: The need for increased thermal efficiency, which provides a reduction in energy consumption, is driving the use of materials with higher temperature capabilities for a variety of applications such as land-based power systems and aircraft engines. These materials are subjected to environmental and thermomechanical extremes for sustained periods during normal operation. The operating conditions are in a regime where several time-dependent damage mechanisms, such as creep deformation, oxygen diffusion, and crack tip oxidation, can operate during cyclic loading and during the dwell period. Therefore, the fundamental mechanisms governing time-dependent damage and degradation must be well understood. During elevated temperature creep-fatigue loading, polycrystalline Ni-base superalloys have exhibited intergranular failure due to oxygen embrittlement. Controlling the grain boundary character distribution (GBCD) has been shown to influence the crack growth rate, but the actual effect on the crack tip kinetics is not well understood. The primary goal of this research endeavor is to assess the influence of the grain boundary character distribution on the crack tip kinetics (i.e. the rates of creep deformation, crack extension, and oxygen diffusion along grain boundaries) of nickel and nickel alloys during elevated temperature creep-fatigue cycling. The crack tip kinetics govern the crack growth rate, so if the kinetics can be quantitatively described as a function of temperature, hold time, and GBCD, then those aspects can be incorporated into a life prediction model.NON-TECHNICAL SUMMARY: The objective of this project is to determine the effect of different amounts of cold working on the elevated temperature fatigue crack growth behavior of nickel and nickel-base superalloys and provide an outreach program that will reach multiple schools and grade levels through an interactive inquiry-based approach. Nickel is the major alloying element in some of the most advanced alloys, which are used in demanding applications, such as land-based power systems, aircraft engines, and chemical processing equipment, and these components require long-term mechanical property retention when exposed to elevated temperature and cyclic loads. Understanding the fatigue behavior during elevated temperature operating conditions is critical to predicting a component?s long-term performance. The research proposed in this project will be integrated with educational activities in a number of ways and for a large range of educational levels, from K-12 to graduate student training. The central component of the K-12 educational outreach will be a program the PI is developing called Metal Madness. The Metal Madness program will be presented in middle school classrooms and will have age-appropriate basic curriculum in what metals are and how they behave. The initial target audience for this program will be the middle schools in the north Alabama region whose student population is predominantly composed of underrepresented groups. The outcomes of this project will increase the understanding of elevated-temperature fatigue while educating graduate and undergraduate students, teachers, high school and middle school students. The outcomes are also expected to improve public safety and well-being through better predictive capabilities for energy producing components, such as aircraft engines and land-based power generation systems.