CAREER: In-situ Hybrid Layerwise Rolling and Sealing in Laser Powder-bed Fusion Manufacturing of Tungsten: Fundamental Processing Mechanisms and Transition Temperature Controls

极高熔化温度的难熔金属和合金，特别是钨（化学符号：W），在太空、国防和核应用等恶劣环境中提供了巨大的应用潜力。由于增材制造能够生产复杂的单件部件，同时减少交货时间和原型成本，因此在钨件的研究和开发中一直在探索增材制造。然而，这种材料固有的脆性和高脆性对其使用高温增材制造（如激光粉末床熔融（LPBF））的生产提出了重大挑战。该学院早期职业发展（Career）基金支持基础研究，该研究将产生与新的混合制造技术相关的知识，在W零件的LPBF过程中，将一层一层的原位轧制和密封结合起来，能够在过程中进行实时修改，从而生产出具有受控和改进性能的零件。该研究将为W零件的先进生产技术提供知识驱动的加工设计，这将为高超声速飞机前沿的波导和准直器以及独特聚变反应堆中的等离子体面向组件等新应用打开大门，从而为加强美国经济和国家安全创造机会。该项目还将设计和提供有趣的实践教育和推广经验，以招收不同类型的高中学生进入STEM专业，并从服务不足的群体中留住本科生和研究生，同时确保他们在STEM相关的职业或研究生教育中取得成功。本次CAREER奖的首要目标是了解在LPBF中分层轧制和密封W的结构和性能演变的机制。该团队将首先研究由轧制和纳米颗粒密封分别引起的塑性变形和强化如何影响W中的热力学驱动力和动力学以及对结构演变的影响，同时遇到熔化和再熔化的过程循环。实验研究将包括原位滚动密封和材料表征技术的LPBF样品制造。晶体塑性、离散位错动力学和元胞自动机模型将被整合，以研究在此过程中位错、微观结构和织构的演变。接下来，该项目将揭示新获得的W结构的基本机制及其在韧脆转变和再结晶发展中的作用。通过断裂韧性测试来研究韧脆转变温度，并辅以裂纹尖端塑性理论和热动力学分析来发现它们各自对转变温度的贡献。此外，将采用退火和显微硬度测试来确定再结晶温度，并使用再结晶动力学模型和热力学原理来确定再结晶驱动力。然后，通过不同温度下的拉伸试验直至断裂，阐明W结构对变形机制和力学行为的影响，评价其强度和延性。此外，还将使用修正的克莱因模型研究塑性行为及其对强度和延性的贡献。研究结果将有助于深入了解原位滚动密封复合材料的热力学和动力学特性，以及它们在各种机械、纳米结构和热约束下对热力学行为的影响。最终，所获得的知识将通过改善零件性能和提高工作温度限制来实现W材料的进步。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。

Refractory metals and alloys of extremely high melting temperatures, particularly tungsten (chemical symbol: W), offer great potential for applications in harsh environments found in the space, defense, and nuclear applications, etc. Additive manufacturing has been explored in the research and development of tungsten parts because of its ability to produce complex single-piece components along with reducing lead times and prototype costs. However, the inherent brittleness and high susceptibility to cracking of this material class pose major challenges to its production using high-temperature additive manufacturing such as laser powder-bed fusion (LPBF). This Faculty Early Career Development (CAREER) grant supports fundamental research that will generate knowledge related to a new hybrid manufacturing technique, combing in-situ rolling and sealing layer-by-layer during LPBF of W parts, capable of performing real-time modifications during the process, and thus, producing parts with controlled and improved properties. The research will enable knowledge-driven processing designs for the advanced production technology of W parts, which would open doors to new applications ranging from waveguides and collimators for hypersonic aircraft leading edges and plasma-facing components in unique fusion reactors, and thereby, create opportunities to strengthen the U.S. economy and national security. This project will also design and deliver intriguing hands-on educational and outreach experiences for the recruitment of diverse high school students to STEM majors and the retainment of undergraduate and graduate students from underserved groups, while ensuring their success in STEM-related careers or post-graduate education.The overarching goal of this CAREER award is to understand the mechanisms that govern the evolution of the structures and properties of W made by layerwise rolling and sealing in LPBF. The team will first investigate how plastic deformation and strengthening, induced by rolling and nanoparticle sealing, respectively, affect the thermodynamic driving forces and kinetics in W as well as impacts on structural evolution, while encountering process cycles of melting and re-melting. Experimental studies will include LPBF sample fabrications with in-situ rolling-sealing and materials characterization techniques. Crystal plasticity, discrete dislocation dynamics, and cellular automata models will be integrated to investigate into the evolution of dislocations, microstructure, and texture during the process. Next, the project will unveil the fundamental mechanisms underlying the newly achieved W structure and its role in the development of ductile-to-brittle transition and recrystallization. Fracture toughness testing will be conducted to investigate the ductile-to-brittle transition temperature, complemented by the crack-tip plasticity theory and thermo-kinetic analysis to discover their respective contributions to the transition temperature. Furthermore, annealing followed by microhardness testing will be employed to identify the recrystallization temperature, with recrystallization kinetic models and thermodynamic principles used to determine the recrystallization driving forces. Then, how the fabricated W structure influence deformation mechanisms and mechanical behavior will be elucidated through tensile testing up to fracture at different temperatures to evaluate the strength and ductility. In addition, the plastic behavior and its contributions toward strength and ductility will be studied using the modified Clyne model. The research findings will offer insights into the thermodynamic and kinetic aspects of the hybrid in-situ rolling-sealing LPBF and their influence on thermal and mechanical behaviors under various mechanical, nano-structural, and thermal constraints. Ultimately, the knowledge attained will enable the advancement of W materials through improving part performance and increasing the operating temperature limits.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.