Deformation Mechanisms Governing Torsional Fatigue Failure of Additively Manufactured Metals at High Temperatures

三维金属打印/添加剂制造技术的最新进展使得镍基金属高温合金零件的实现和快速生产成为可能，扩大了其几何设计空间和机械性能范围。然而，有必要确保这些额外制造的部件在满足必要的功能要求和耐用性的同时，能够承受服务中的操作条件。以循环扭转载荷为特征的扭转疲劳往往是火箭和喷气发动机、高性能汽车和压力容器等极端环境中使用的镍基金属高温合金失效的根本原因。这些极端温度环境的特点是加载状态复杂，导致扭转疲劳破坏的变形机制尚不清楚。该奖项支持基础研究，以描述微观结构水平上的主要变形机制，这些机制管理添加制造的镍基金属高温合金在不同使用条件下的扭转疲劳失效。这项研究将提高目前的知识水平，最大限度地提高这些合金在使用中的耐用性和可行性，从而使当前的技术成熟。此外，这项研究将扩大未被充分代表的少数族裔本科生和研究生在STEM研究中的参与、拓展和专业培训，这些研究跨越机械、制造、材料科学和工程等学科。研究成果将被用来建立增强的教育课程/工具，包括纳入基于研究项目的教学结构。这项研究解决的基本问题是捕捉添加制造的镍高温合金在代表在役部件条件下的扭转疲劳载荷条件下从微米尺度到结构尺度的变形响应谱。将探索温度、变化的循环扭转载荷以及附加制造工艺条件和建造方向的作用。各种材料表征技术，如能量色散光谱、X射线衍射和电子显微镜，将与广泛的疲劳试验结合使用，以捕捉导致扭转疲劳裂纹萌生和扩展的驱动微观结构机制。预计这项研究的结果将揭示这些合金在环境和运行条件下的微观结构演变对扭转响应的影响，潜在地提供有助于了解其多轴疲劳响应的见解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Recent advances in the 3D metal printing/additive manufacturing technology have allowed for the realization and rapid production of nickel-based metal superalloy components, extending their geometric design space and mechanical performance envelope. Nevertheless, there is a need to ensure that these additively manufactured components can withstand in-service operational conditions while meeting necessary functional requirements and durability. Torsional fatigue, characterized by cyclic twisting loads, is often an underlying cause for failure of nickel-based metal superalloys used in the extreme environments of rocket and jet engines, high performance automobiles, and pressure vessels. These extreme temperature environments are characterized by a complex loading state, in which the deformation mechanisms contributing to torsional fatigue failure remain unclear. This award supports fundamental research to delineate the principal deformation mechanisms at the microstructural level, which govern torsional fatigue failure of additively manufactured nickel-based metal superalloys subject to varying service conditions. This research will advance the current state of knowledge and maximize durability and viability of these alloys for in-service use, thereby maturing the current technology. Additionally, this study will broaden participation, outreach, and professional training of under-represented minority undergraduate and graduate students in STEM research spanning across the disciplines of mechanics, manufacturing, and materials science and engineering. Research outcomes will be used to establish enhanced educational curriculum/tools, including incorporation of a research project-based teaching and learning structure.The fundamental problem that this research addresses is capturing the micron scale to structural scale deformation response spectrum experienced by additively manufactured nickel superalloys under torsional fatigue loading conditions at ambient and high temperatures representing in-service component conditions. The role of temperature, varying cyclic torsional loadings, and additive manufacturing processing conditions and build orientation will be explored. A variety of material characterization techniques, such as energy dispersive spectroscopy, X-ray diffraction, and electron microscopy, will be used in conjunction with extensive fatigue testing to capture the driving microstructural mechanisms leading to torsional fatigue crack initiation and growth. It is anticipated that outcomes resulting from this study will reveal how torsional response of these alloys is impacted in terms of microstructural evolution under ambient and in-service operational conditions, potentially providing insights that will contribute to an understanding of their multiaxial fatigue response.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.