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-延展性权衡;给定的材料越强，其延展性就越小。已经研究了常规合金的晶粒结构细化以提高强度和延展性。 然而，迄今为止，仍不清楚如何将晶粒细化有效地应用于复杂浓缩合金（CCA），其在组成上与多种主要化学元素化合，通过增材制造制成。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，以测试一个假设，即增加熵（即，无序程度）将延缓晶粒粗化并稳定微观结构，从而实现高强度和高延展性。研究结果将弥合微结构工程在高温和其他关键应用中的CCA设计和增材制造方面的知识差距。与此同时，制定的外联活动将促进研究和教育，培养先进制造业的下一代研究人员和STEM领导者，本研究的总体目标是了解通过不同合金粉末的混合物和随后的添加剂制造的CCA中晶粒细化的潜在机制。熔化和固化。该项目将研究复杂成分空间中的晶粒生长动力学和相稳定性，使用由机器学习增强建模，高通量制造实验以及微观结构和材料表征组成的有效研究工具包。本研究将通过探索使用基于粉末的增材制造技术从异种合金生成的微结构配置，解决与CCA增材制造的微结构工程相关的知识需求（定向能量沉积和粉末床熔合，两者都使用激光热源），具有以下预期结果：（i）量化合金熵对工艺-结构-性能关系的影响，以揭示用细化晶粒或其他手段强化CCA的基本机制，（ii）CCA中的微观结构形成，以了解通过基于粉末的增材制造制成的复杂浓缩合金与传统合金之间的差异，和（iii）工艺-结构-性能模型，以在不锈钢和镍之间的组成空间中专门为CCA建立。该奖项反映了NSF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.