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

技术概要：对提高热效率的需求，这提供了减少能源消耗，正在推动使用具有更高温度能力的材料用于各种应用，如陆基电力系统和飞机发动机。 这些材料在正常运行期间会持续经受环境和热机械极端条件。的操作条件是在一个政权，其中几个时间依赖性的损伤机制，如蠕变变形，氧扩散，裂纹尖端氧化，可以在循环加载过程中，并在停留期间。因此，必须很好地理解与时间相关的损害和退化的基本机制。 多晶镍基高温合金在高温蠕变疲劳载荷下，由于氧脆化而出现沿晶失效。 控制晶界特征分布（GBCD）已被证明会影响裂纹扩展速率，但对裂纹尖端动力学的实际影响还没有得到很好的理解。 本研究奋进的主要目标是评估晶界特征分布对镍和镍合金在高温蠕变疲劳循环过程中裂纹尖端动力学（即蠕变变形、裂纹扩展和氧沿沿着晶界扩散的速率）的影响。 裂纹尖端动力学控制裂纹扩展速率，因此，如果动力学可以定量描述为温度、保持时间和GBCD的函数，则这些方面可以纳入寿命预测模型。本项目的目的是确定不同的冷加工量对镍和镍基合金高温疲劳裂纹扩展行为的影响，基地高温合金，并提供一个推广计划，将达到多个学校和年级通过互动式调查为基础的方法。 镍是一些最先进的合金中的主要合金元素，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时需要长期保持机械性能。 了解高温运行条件下的疲劳行为对预测组件至关重要？的长期业绩。 本项目中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到研究生培训的各种教育水平。 K-12教育推广的核心组成部分将是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提出，并将有适合年龄的基本课程，在什么是金属和他们如何表现。 该计划的最初目标受众将是北亚拉巴马地区的中学，其学生人口主要由代表性不足的群体组成。 本计画的成果将增进对高温疲劳的了解，同时教育研究生、本科生、教师、高中生和中学生。这些成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来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.