CAREER: Wire Arc Additive Manufacturing of Molybdenum Alloys for High-temperature Applications: Residual Stresses and Porosity Considering Ductile-to-brittle Transition Temperature

难熔金属如钼（Mo）基合金由于其高熔点而具有在恶劣环境中应用的巨大潜力。然而，Mo合金具有几个固有的缺点，例如低延展性以及氧化和开裂的倾向，当它们通过增材制造生产时，由于非平衡加工现象，这些缺点不利地增加。这导致了几个复杂的技术障碍，阻碍了钼合金增材制造在工业中的广泛采用。该学院早期职业发展（CAREER）项目旨在对钼合金结构的电弧增材制造（WAAM）进行基础研究，并将探索和阐明加工缺陷的根本原因及其对零件热机械性能的影响。如果成功，这项研究将直接影响国家的经济福利和能源安全。例如，陆地发电厂的能源效率可以通过使用钼合金制造涡轮机叶片来提高，碳足迹可以减少。此外，该项目还将通过数据分析组件增强现有的制造课程，为本科生/研究生提供在国家实验室实习的机会，并为K-12学生提供实践制造经验。该奖项的总体研究目标是了解工艺引起的残余应力以及孔隙产生的潜在机制，并研究WAAM加工钼合金结构的热机械性能，重点关注钛锆钼合金。核心研究的挑战在于缺乏数据的物理化学性质和复杂的缺陷发展的非平衡热循环在层逐层堆叠。结合计算和物理信息，数据驱动的模型将被用于工艺理解与实验验证和确认，包括多尺度材料表征，工艺成像和疲劳测试等。该研究预计将获得残余应力发展和孔隙形成的基础知识，同时考虑韧脆转变温度，并阐明了从室温到高温的变形行为和热机械性能，以及与非均匀微观结构、孔隙和氧化相关的变形行为和热机械性能。此外，该项目还打算为WAAM建立工艺、特征、微观结构、性质和性能之间的定量关系，称为“设计规则”，以确保耐火合金结构的制造令人满意。这种联系可以作为一种有效的工具，有可能定制微观结构和性能的WAAM结构与控制和改进的热机械性能的最终products.This奖项反映了NSF的法定使命，并已被认为是值得的支持，通过评估使用基金会的智力价值和更广泛的影响审查标准。

Refractory metals such as Molybdenum (Mo) based alloys have a great potential for applications in harsh environments, because of their high melting point. However, Mo alloys have several inherent drawbacks such as low ductility and a tendency of oxidation and cracking, which are adversely augmented when they are produced by additive manufacturing, due to non-equilibrium processing phenomena. This results in several complex technical blockades that hinder a broader adoption of additive manufacturing of Mo alloys in the industry. This Faculty Early Career Development (CAREER) project aims at fundamental research of wire arc additive manufacturing (WAAM) for Mo alloy structures, and will explore and elucidate the root causes of processing defects and their effects on part thermomechanical performance. If successful, the research will directly impact the Nation’s economic welfare and energy security. For example, the energy efficiency of land-based power plants could be improved and their carbon footprint decreased by using Mo alloys for turbine blades. In addition, the project will enhance the existing manufacturing curricula with data analytics components, provide undergraduate/graduate student with internship opportunities at national laboratories, and run hands-on manufacturing experiences for K-12 students. The outreach activities will enhance the education and training of next-generation STEM leaders in advanced manufacturing and foster inclusions of underrepresented groups.The overarching research goal of this CAREER award is to understand the underlying mechanisms of process-induced residual stresses as well as pore generation and investigate thermomechanical performances of WAAM processed Mo-alloy structures, focusing on titanium-zirconium-molybdenum alloys. The core research challenges lie on the lack of data in the physicochemical properties and complex defects development from non-equilibrium thermal cycles in layer-by-layer stacking. A combination of computational and physics-informed, data-driven models will be pursued for process understanding with experimental verifications and validations, including multi-scale material characterizations, process imaging and fatigue testing, etc. The research is expected to gain fundamental knowledge of the residual stress development and pore formation while considering the ductile-to-brittle transition temperature, and elucidate the deformation behaviors and thermomechanical performances from room to elevated temperatures, as correlated with heterogeneous microstructures, pores and oxidation. In addition, the project intends to establish a quantitative relationship between the process, signature, microstructure, property and performance, called the “design rule,” for WAAM that will ensure satisfactory fabrications of refractory alloy structures. The linkage may serve as an effective tool to potentially tailor microstructures and properties of WAAM structures with controlled and improved thermomechanical performance of final products.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.