CAREER: Understanding thermal phase change processes in metal additive manufacturing

基于激光的添加制造，包括3D金属打印，通过允许制造商制造可以高度定制的复杂形状的部件，并使融入成分和微结构的图案成为可能，最终可能导致新的材料类别和应用，从而使制造过程发生革命性变化。然而，加法制造的广泛实施受到两个方面的限制，一是技术问题，如缺乏质量控制和零件到零件的可重复性；二是社会因素，如工程劳动力的准备程度。机械性能，如强度、硬度和抗疲劳性--对任何承重部件来说都是重要的参数--由材料的微观结构决定。这些材料特性又受工艺细节的制约：激光特性、熔化材料的行为、凝固以及随时间推移的工件温度。金属的不透明度以前限制了研究熔化材料的行为和凝固机制的能力。通过创新的研究和教育方法，该项目解决了实施添加剂制造方面的挑战，包括微观结构和缺陷控制等技术方面，以及劳动力发展，为广泛实施稳健和可靠的添加剂工艺奠定了基础。该跨学科项目的科学重点是全面了解基于激光的成分梯度金属添加剂制造中控制粉末熔化、对流混合和凝固的热过程。使用光学透明代理系统的非原位实验能够表征相变和流体混合。在初步实验的基础上，将重点介绍两种情况：i)粉末撞击位置对熔融和混合的影响；ii)不同材料的熔融、混合和凝固。利用独特的高速原位热红外成像装置，能够在毫秒级捕捉熔池内的瞬变事件，将量化两种金属过渡区的凝固动力学。通过建立将工艺参数与微结构和缺陷发展相结合的基本框架，非原位和原位测量与沉积后材料表征的相关性有可能导致添加剂制造的变革性进步。利用3D打印的魅力，教育活动旨在扩大和深化年轻人对科学和工程的参与。这些活动的核心是开发3D巧克力打印机，它将亲身实践的科学学习体验与高速成像的吸引力结合在一起，为K-12和本科生提供不同的学习模块。一个特别的重点是通过提供对添加剂制造和热流体科学的有趣和低风险的介绍来增强中学年龄的女孩在STEM中的职业生涯。该奖项反映了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。

Laser-based additive manufacturing, including 3D metal printing, has revolutionized manufacturing processes by allowing manufacturers to make parts with complicated shapes that can be highly customized and making it possible to incorporate patterns of composition and micro-structure that may ultimately lead to new classes of materials and applications. Yet widespread implementation of additive manufacturing is limited by both technical issues, such as lack of quality control and part-to-part repeatability, and societal factors, such as the readiness of the engineering workforce. Mechanical properties, such as strength, hardness, and fatigue resistance – important quantities for any load-bearing component - are dictated by the material microstructure. These material properties are, in turn, governed by the details of the process: laser characteristics, the behavior of melted material, solidification, and the temperature of the workpiece over time. The opacity of metal has previously limited the ability to study the behavior of the melted material and the mechanism of solidification. Through an innovative research and educational approach, this project addresses challenges in implementing additive manufacturing, both the technical aspects, including microstructure and defect control, and the workforce development, laying the foundation for the broad implementation of robust and reliable additive processes.The scientific focus of this interdisciplinary project is to provide a comprehensive understanding of the thermal processes governing powder melting, convective mixing, and solidification in laser-based additive manufacturing of compositionally graded metals. Ex-situ experiments using an optically transparent surrogate system enable the characterization of phase change and fluid mixing. Based on preliminary experiments, two scenarios will be highlighted: i) the influence of powder impact location on melting and mixing, and ii) melting, mixing, and solidification of dissimilar materials. Using a unique in-situ high-speed thermal infrared imaging setup, capable of capturing transient events within the melt pool at the millisecond time scale, solidification dynamics in the transition zone of two metals will be quantified. Correlation of ex-situ and in-situ measurements along with post-deposition material characterization has the potential to lead to transformative advancements in additive manufacturing by creating a fundamental framework to couple process parameters with microstructural and defect development. Leveraging the fascination of 3D printing, educational activities aim at broadening and deepening participation of young people in science and engineering. At the core of these activities is the development of a 3D chocolate printer, which integrates hands-on scientific learning experiences with the appeal of high-speed imaging with different learning modules for both K-12 and undergraduate students. A specific focus is on empowering middle-school aged girls to pursue careers in STEM by providing a fun and low-stake introduction to additive manufacturing and thermal-fluid sciences.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.