RII Track-4: NSF: Development, Characterization and Performance Evaluation of Surface Engineered Additively Manufactured Parts for Nuclear Reactors

金属增材制造（AM）自发明以来发展迅速。在本项目中，将利用激光定向能沉积（DED）工艺制造核反应堆用金属部件。顶部几层将进一步采用超声波冲击强化处理，以提高其耐磨性。打印后，将使用中子衍射分析样品，以揭示沿制造样品构建方向不同构建高度区域的微观结构，残余应力和相分数的演变，以将微观结构细节与工艺条件联系起来。这些增材制造的样品的摩擦磨损行为将通过往复滑动和微动磨损测试来进行。摩擦学是研究摩擦、磨损和润滑的科学，与表面工程有着内在的不可分割性。增材制造提供了独特的功能，可以用来提高各种摩擦学接触的可靠性。该项目将探讨增材制造、表面工程和摩擦学之间的共生关系，特别是与核反应堆相关的滑动和微动接触问题。然而，这项研究的主要发现将为生物医学、汽车和航空航天等关键应用领域的各种接触提供有价值的见解。这个研究基础设施改善轨道4 EPSCoR研究研究员（RII轨道4）项目将为北达科他州大学（UND）的助理教授提供奖学金并为研究生提供培训。摩擦学是研究摩擦、磨损和润滑的一门复杂的跨学科学科。为了实现适当的商业化，有必要了解增材制造部件与传统制造部件相比摩擦和磨损机制的差异，并深入了解材料特性。表面工程与材料科学有关，因为它涉及固体物质的表面。增材制造、表面工程和摩擦学有着相互依存的关系。我们的研究目标是利用这一观点来开发下一代核反应堆组件，这些组件在不同温度下遇到摩擦和磨损时具有更高的可靠性和可定制性。我们将利用定制的激光定向能沉积（DED）技术，配备超声波冲击强化（UIP）能力，制造由nitrononic 60不锈钢制成的功能梯度金属部件。氮60是一种廉价的奥氏体不锈钢，因其耐磨损性能而广泛应用于核领域。这种材料可以呈现高温磨损和耐腐蚀性，广泛应用于阀座、衬套、滚子轴承和密封圈。我们认为，在UIP处理过程中，优化的工艺参数可以导致Nitronic 60近表面沉积层的应变诱导FCC到HCP马氏体相变（SIM），并且增强材料状态，例如具有细化晶粒的残余应力，可以改善摩擦学行为。通过中子衍射了解相组分、残余应力沿构建高度的演化规律，并将其与往复摩擦磨损测试以及加工样品的网格-棒微动特性相关联，揭示沉积的Nitronic 60的工艺-显微组织-性能。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。

Metal additive manufacturing (AM) has developed significantly since its invention. In this project, a laser-based directed energy deposition (DED) process will be utilized to fabricate metallic parts for nuclear reactor application. The top few layers will be further engineered using an ultrasonic impact peening treatment to enhance its wear resistance. Post printing, the samples will be analyzed using neutron diffraction to reveal the evolution of microstructure, residual stress, and phase fractions at different build height regions along the build direction of fabricated samples to correlate the microstructural details with process conditions. Friction and wear behavior of these additively manufactured samples will be conducted via both reciprocating sliding and fretting wear testing. Tribology is the science of friction, wear, and lubrication, making it inherently inseparable from surface engineering. AM offers unique capabilities that can be leveraged to enhance the reliability of various tribological contacts. This project will explore the symbiotic relationship between AM, surface engineering, and tribology with respect to sliding and fretting contact problems specifically connected to nuclear reactors. However, the major findings from this research will provide valuable insights to wide varieties of contacts in critical applications, such as biomedical, automotive, and aerospace sectors.This Research Infrastructure Improvement Track-4 EPSCoR Research Fellows (RII Track-4) project would provide a fellowship to an Assistant professor and training for a graduate student at the University of North Dakota (UND). Tribology, a complex and highly interdisciplinary field, is the science of friction, wear, and lubrication. It is necessary to understand the differences in an AM part’s friction and wear mechanism compared to traditionally fabricated parts and in-depth material characterizations for proper commercialization. Surface engineering is connected to materials science since it pertains to the surface of solid matter. Additive manufacturing, surface engineering, and tribology have an interdependent relationship. Our research goal is to leverage this perspective to develop next-generation nuclear reactor components with enhanced reliability and customizability when encountering friction and wear at different temperatures. We will fabricate functionally graded metallic components made of Nitronic 60 stainless steel by leveraging customized laser-based directed energy deposition (DED) technique equipped with an ultrasonic impact peening (UIP) capability. Nitronic 60 is an inexpensive austenitic stainless steel widely used in the nuclear sector due to its galling-resistance properties. This material can present high-temperature wear and corrosion resistance, and widely used in valve seats, bushings, roller bearings, and rings. We believe that optimized process parameters during UIP treatment can result in a strain-induced FCC to HCP martensitic phase transformation (SIM) in the deposited near-surface layers of Nitronic 60, and enhanced materials states, such as residual stress with refined grains, can result in improved tribological behavior. Process-microstructure-property of deposited Nitronic 60 will be revealed by understanding phase fractions, residual stress evolution along build height through neutron diffraction and correlated that with reciprocating friction and wear testing as well as grid-to-rod fretting characteristics of fabricated samples.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.