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

金属3D打印/增材制造技术的最新进展使得镍基金属高温合金部件的实现和快速生产成为可能，扩展了它们的几何设计空间和机械性能。然而，需要确保这些增材制造的部件能够承受在役操作条件下，同时满足必要的功能要求和耐用性。以循环扭转载荷为特征的扭转疲劳，通常是在火箭和喷气发动机、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潜在原因。这些极端温度环境具有复杂的加载状态，其中导致扭转疲劳破坏的变形机制尚不清楚。该奖项支持在微观结构水平上描述主要变形机制的基础研究，这些机制决定了增材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。这项研究将推进当前的知识状态，并最大限度地提高这些合金在服役中的耐久性和可行性，从而使当前的技术成熟。此外，这项研究将扩大少数民族本科生和研究生在机械、制造、材料科学和工程等学科的STEM研究中的参与、推广和专业培训。研究成果将用于建立更完善的教育课程/工具，包括纳入以研究项目为基础的教与学结构。本研究解决的基本问题是捕获增材制造的镍高温合金在环境和高温下的扭转疲劳载荷条件下所经历的微米尺度到结构尺度的变形响应谱。将探讨温度、不同的循环扭转载荷、增材制造的加工条件和构建方向的作用。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，将与广泛的疲劳测试结合使用，以捕获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的扭转响应在环境和服役操作条件下的微观结构演变方面是如何受到影响的，这可能有助于了解它们的多轴疲劳响应。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.