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

基于熔炼的添加剂制造(AM)已被用于制造高价值金属零件。然而，由于工艺温度高(通常超过部件材料的熔点)以及相关的大的温度梯度和快速冷却速度，存在局限性。另一方面，不熔化的金属AM，如冷喷涂技术，将微小的粉末颗粒加速到超音速，在撞击时碰撞、结合并形成底层材料，可能会大大缓解熔化根源的挑战。该学院早期职业发展(CALEAR)奖支持研究，利用新颖的高速单颗粒冲击试验，辅之以多尺度数值模拟，发展对冷喷涂AM的工艺-显微结构-性能关系的基本理解，以研究单个结合颗粒，冷喷涂工艺的基石，然后扩展到部分水平的研究。这项研究将使冷喷涂AM的可靠和面向性能的工艺设计成为可能，并有可能通过实现可持续和敏捷的制造和在需要时进行维修来加强国家国防和其他行业。所获得的知识也可以转化为用于航空航天、建筑和能源应用的其他固态连接或添加技术。该团队将通过设计添加剂制造工具包的实践活动，让K-12学生和教育工作者参与进来。该项目还将通过在研究实验室举办为期10周的夏令营，促进未被充分代表的少数民族学生参与先进制造业。该职业项目的总体目标是建立一个统一的框架，以了解和预测冷喷涂沉积的临界速度、冲击诱导的微结构发展、微观结合强度和宏观力学性能。激光诱导的微尺度弹丸撞击试验将用高分辨率成像进行，以产生清晰的高速单个结合颗粒，具有先进的电子显微镜和微观机械测量表征的微观结构和特性。将系统地研究第一层碰撞和颗粒对后续各层的碰撞。科学地揭示了冲击速度、氧化层厚度、颗粒大小和温度、冲击角度等因素对结合界面特征和局部结合强度的影响。此外，还将建立基于位错的本构模型、氧化层断裂和粘结的有限元模型，用于预测冲击引起的微观组织变化和结合强度。微观模拟将为宏观模型提供信息，以计算冷喷涂试件的力学性能。由于颗粒大小、温度和氧化层厚度的分布而产生的统计效应的不同来源也将在多尺度模型中被考虑。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.