Phase Field Modeling of Thermal Transport for Predicting and Preventing Porosity and Solidification Cracking in Additive Manufacturing

该项目考虑了用于航空航天、汽车、海军、石油和能源等行业的高端增材制造金属产品的几何精度和机械质量。对高温过程（如激光加热如何与金属粉末相互作用以及粉末熔化和融合过程中表面缺陷如何演变）的基本了解是增材制造成功的关键。本项目通过理论分析和实验验证，重点预测和预防凝固裂纹等表面缺陷的形成。该项目将帮助美国制造业制定战略，以提高增材制造制造的关键金属部件的机械性能。具体而言，该项目将使金属材料供应商、制造机器设计师、产品设计师和最终用户受益。高等教育和多元化的劳动力培训是下一代制造领域工程师的重点。高强度合金增材制造的主要障碍是几何精度、表面质量和对机械性能的追求。在增材制造中，气孔、缺口和裂纹等缺陷通常是由粉末的不完全熔化、界面不稳定、蒸发和反冲、成球、飞溅和凝固过程中的裂纹引起的。在粉末和微观结构水平上对过程动力学进行预测建模以减轻上述机制引起的缺陷是非常必要的。该项目的目标是为此目的建立一个完整的相场理论框架。该项目包括三个具体任务：(i)通过一个完全耦合的热、流体、相变和微观结构演化模型来解决孔隙率的动力学和分布问题；（ii）将热流体动力学与弹性、塑性、晶粒微观结构演化和凝固开裂的敏感性结合起来；（iii）利用NIST增材制造基准测试系列（AM-Bench）从微观结构到热力学分析的可用数据进行实验验证和不确定性分析。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。

This project considers the geometry accuracy and mechanical quality of high-end additively manufactured metal products used in aerospace, automobile, naval, petroleum, and energy industries. Basic understanding of the high temperature process such as how laser heating interacts with metallic powders and how surface defects evolve during powder melting and fusion is key to the success of additive manufacturing. Through theoretical analysis and experimental validation, this project focuses on predicting and preventing the formation of surface defects including solidification cracks. The project will help manufacturing industry in the U.S. to develop strategies to increase mechanical performance of critical metallic parts made by additive manufacturing. Specifically, this project will benefit metallic material suppliers, manufacturing machine designers, product designers and end users. Higher education and workforce training with diversity are emphasized for the next generation of engineers in manufacturing field. The primary road block on additive manufacturing of high strength alloys is geometric accuracy, surface quality, and the quest for mechanical performance. Defects such as pores, notches, and cracks in additive manufacturing are often caused by incomplete melting of powders, interfacial instability, evaporating and recoiling, balling, spattering, and cracking during solidification. There is a great need on predictive modeling of the process dynamics at powder and microstructure levels to mitigate defects caused by above mechanisms. The project goal is to establish an integrated phase field theoretical framework for this purpose. The project includes three specific tasks: (i) resolve the dynamics and distribution of porosity by a fully coupled thermal, fluids, phase transition, and microstructure evolution model, (ii) integrate thermal fluid dynamics with elasticity, plasticity, grain microstructure evolution, and susceptibility of solidification cracking, (iii) perform experimental validations and uncertainty analysis using available data from NIST Additive Manufacturing Benchmark Test Series (AM-Bench) ranging from microstructure to thermal mechanical analysis.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.