CAREER: Unraveling Fundamental Mechanisms Governing Grain Refinement in Complex Concentrated Alloys Made by Additive Manufacturing Towards Strong and Ductile Structures

生产坚固而坚韧的结构合金的能力一直是充分利用材料和制造的集成创新的追求。一个长期存在的挑战是众所周知的强度-延性权衡；给定的材料越强，它的延展性就越差。为了提高合金的强度和延展性，对传统合金进行了细化晶粒组织的研究。然而，迄今为止，晶粒细化如何有效地应用于复杂浓缩合金（CCAs）仍不清楚，这些合金是由多种主要化学元素组成的化合物，由增材制造制造。该学院早期职业发展（Career）奖支持对cca增材制造的基础研究。该项目将进行不同的研究，以验证一个假设，即增加合金系统中的熵（即无序水平）将延缓晶粒粗化并稳定微观结构，从而实现强大的强度和高延展性。该研究成果将弥补高温和其他关键应用CCAs的微结构工程设计和增材制造方面的知识差距。与此同时，制定的外展活动将促进研究和教育，以培训下一代先进制造业的研究人员和STEM领导者，特别是促进妇女和少数民族参与制造业和相关领域。本研究的首要目标是了解通过不同合金粉末的混合物以及随后的熔化和固化，通过增材制造制造的CCAs晶粒细化的潜在机制。该项目将使用一个有效的研究工具包，包括机器学习增强建模、高通量制造实验以及微观结构和材料表征，研究复杂成分空间中的晶粒生长动力学和相稳定性。本研究将通过探索使用粉末基增材制造技术（定向能沉积和粉末床融合，均使用激光热源）由不同合金产生的微观结构配置，解决与cca增材制造的微观结构工程相关的知识需求，并获得以下预期结果：(i)量化合金熵对工艺-结构-性能关系的影响，以揭示用细晶或其他方法强化cca的基本机制；（ii） cca中的微观结构形成，以了解由粉末基增材制造制造的复杂浓缩合金与传统合金之间的区别；（iii）在不锈钢和镍基高温合金之间的成分空间中，专门为cca建立工艺-结构-性能模型。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。

The ability to produce strong yet tough structural alloys has been a quest to fully exploit the integrated innovation of materials and manufacturing. One longstanding challenge is the well-known strength-ductility trade-off; the stronger a given material is, the less ductile it becomes. Grain structure refinements have been studied for conventional alloys to enhance both the strength and ductility. To date, however, it remains unclear how grain refinements may be effectively applied to complex concentrated alloys (CCAs), which are compositionally compound with multiple principal chemical elements, made by additive manufacturing. This Faculty Early Career Development (CAREER) award supports fundamental investigations into additive manufacturing of CCAs. The project will perform different studies to test a hypothesis that increasing the entropy (i.e., level of disorder) in an alloy system will retard grain coarsening and stabilize microstructures, and thus, achieve both great strengths and high ductility. The research findings will bridge the knowledge gaps of microstructure engineering in designs and additively manufacturing of CCAs for high temperature and other critical applications. In concert, the formulated outreach activities will advance the research and educations in training the next generation of researchers and STEM leaders in advanced manufacturing, specifically fostering inclusions of women and minorities in manufacturing and related fields.The overarching goal of this research is to understand the underlying mechanism of grain refinements in CCAs made by additive manufacturing through a mixture of dissimilar alloy powders and subsequent melting and solidifying. The project will investigate grain growth kinetics and phase stability in complex composition space, using an effective research toolkit comprised of machine-learning enhanced modeling, high-throughput fabrication experiments, as well as microstructural and material characterizations. This research will address knowledge needs related to microstructure engineering for the additive manufacturing of CCAs by exploring microstructure configurations generated from dissimilar alloy using powder-based additive manufacturing technologies (directed energy deposition and powder-bed fusion, both using a laser heat source) with following expected outcomes: (i) quantification of alloy entropy effects on process-structure-property relationships to reveal the fundamental mechanism to strengthen CCAs with refined grains or other means, (ii) microstructure formation in CCAs to understand the difference between complex concentrated vs. traditional alloys made by powder based additive manufacturing, and (iii) process-structure-property models to establish specifically for CCAs in the composition space between stainless steels and nickel-based superalloys.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.