CAREER: Understanding Bond Formation, Microstructural Development and Mechanical Properties in Cold Spray Additive Manufacturing – A Unified Experimental and Numerical Approach

基于熔融的增材制造（AM）已被用于高价值金属部件的制造。然而，由于较高的工艺温度（通常超过组件材料的熔点），以及相关的大热梯度和快速冷却速率，存在局限性。另一方面，不熔化的金属增材制造技术，如冷喷涂技术，将微小的粉末颗粒加速到超音速，在撞击时与底层材料碰撞、结合并形成底层材料，可能会大大缓解熔化带来的挑战。该学院早期职业发展（Career）奖支持对冷喷涂AM的工艺-微观结构-性能关系进行基本理解的研究，使用新型高速单颗粒冲击测试，辅以多尺度数值模拟，研究单个粘合颗粒，冷喷涂过程的组成部分，然后扩展到部分水平的研究。该研究将为冷喷涂增材制造提供可靠和以性能为导向的加工设计，有可能通过在需要时实现可持续和敏捷的制造和维修来加强国防和其他工业。所获得的知识也可以转化为航空航天、建筑和能源应用的其他固态连接或添加剂技术。该团队将通过设计的增材制造工具包参与K-12学生和教育工作者的实践活动。该项目还将通过在研究实验室举办为期10周的夏令营，促进少数族裔学生参与先进制造业。CAREER项目的总体目标是建立一个统一的框架来理解和预测冷喷涂镀层的临界速度、冲击诱导的微观组织发展、微观尺度的结合强度和宏观尺度的力学性能。激光诱导的微尺度弹丸冲击测试将通过高分辨率成像进行，以产生定义明确的高速单个结合颗粒，其微观结构和性能通过先进的电子显微镜和微观力学测量来表征。将系统地研究第一层的影响和粒子对后续层的影响。科学地揭示了冲击速度、氧化层厚度、颗粒尺寸和温度、冲击角度对键合界面特性和局部键合强度的影响。此外，将建立基于位错的本构模型、氧化层断裂和内聚键合的有限元模型，用于预测冲击诱导的微观结构变化和键合强度。微观尺度的模拟将为宏观尺度的模型提供信息，以计算冷喷涂试样的力学性能。在多尺度模型中，还将考虑由粒度分布、温度和氧化层厚度引起的统计效应的不同来源。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。

Melting-based additive manufacturing (AM) has been utilized for high-value metallic component manufacture. Limitations exist, however, due to the high process temperatures, (often beyond the melting point of component materials), and the large associated thermal gradients and rapid cooling rates. On the other hand, non-melting metal AM such as cold spray technology, in which tiny powder particles are accelerated to a supersonic speed to collide, bond to and build up underlying materials upon impact, may considerably alleviate the melting-rooted challenges. This Faculty Early Career Development (CAREER) award supports research in developing a fundamental understanding of the process-microstructure-property relationships for cold spray AM using novel high-speed single-particle impact testing, complemented by multi-scale numerical modeling, to study individual bonded particles, the building blocks of the cold spray process, and then expand to a part-level study. The research will enable reliable and performance-oriented processing design for cold spray AM, with a potential to strengthen the Nation’s defense and other industries through enabling sustainable and agile manufacturing and repair at the point of need. The knowledge gained may also be translated to other solid-state joining or additive technologies for aerospace, construction and energy applications. The team will engage K-12 students and educators through hands-on activities with a designed additive manufacturing toolkit. The project will also promote participation from underrepresented minority students in advanced manufacturing through 10-week summer camps in a research laboratory.The overall goal of this CAREER project is to establish a unified framework to understand and predict the critical velocity, impact-induced microstructural development, micro-scale bond strength, and macro-scale mechanical properties of cold-sprayed deposits. Laser-induced micro-scale projectile impact testing will be conducted with high-resolution imaging to produce well-defined high-velocity individual bonded particles, with microstructures and properties characterized by advanced electron microscopy and micro-mechanical measurements. Both the first layer impacts and particle impacts on subsequent layers will be systematically investigated. The role of the impact velocity, oxide layer thickness, particle size and temperature, and impact angle in the characteristics of bonded interfaces and local bond strengths will be scientifically revealed. Further, finite element modeling incorporating a dislocation-based constitutive model, oxide layer fracture, and cohesive bonding will be established, which will be used to predict the impact-induced microstructure changes and bond strengths. The micro-scale simulations will inform a macro-scale model to calculate the mechanical properties of cold-sprayed specimens. Different sources of statistical effects resulting from the distribution of particle sizes, temperatures, and oxide layer thicknesses will also be considered in the multi-scale model.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.