ERI: Understanding Austenite Refinement Mechanism in Nickel-Alloyed Ductile Cast Irons

ERI：了解镍合金球墨铸铁中的奥氏体细化机制

• 批准号: 2301570
• 负责人: Jingjing Qing
• 金额: $ 19.56万
• 依托单位: Georgia Southern University Research and Service Foundation, Inc
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-06-01 至 2025-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2301570&HistoricalAwards=false
• 关键词: ERI; Understanding; Austenite; Refinement; Mechanism

This Engineering Research Initiation (ERI) grant enables fundamental understanding of refining austenite grain structure in nickel-alloyed ductile irons. Compared to steel and non-ferrous alloys, ductile iron castings are easy to manufacture by established metal casting processes. Ductile irons are widely used to produce structural components in automotive, agriculture, mining, construction, municipal water/sewer, and defense industries and are easily recyclable. This research is aimed at providing an economical method to improve mechanical properties of the as-cast ductile iron via refining its grain structure without the need of large amounts of expensive alloying element additions or energy-intensive heat treatment. This award supports fundamental research to provide the needed knowledge for the development of a robust in-situ grain refinement process for austenitic ductile iron. The refined grain structure improves the strength and toughness of the ductile iron, which leads to the development of higher strength-to-mass ratio castings and thinner section and lighter weight components. The benefits of lightweight ductile iron cast parts are reduced energy consumption and carbon emission during production, service, and recycling, which benefits the U.S. economy and society. This research involves several disciplines including metallurgy, materials science, and manufacturing. The multi-disciplinary approach helps broaden participation of women and underrepresented students in research and positively impacts engineering education.Refinement of austenite in ductile iron can result in a finer final microstructure improving its mechanical properties. However, the approach to achieve in-situ austenite grain refinement during the melting and solidification process and the associated mechanisms are not well understood. A nickel-alloyed ductile iron is designed with thermodynamic equilibrium calculations to retain austenite structure during solidification. Four elemental additions, cerium, titanium, aluminum, and bismuth are selected. The selected alloying additions are hypothesized to refine the austenite microstructure either by promoting heterogeneous nucleation of austenite grains, or by impeding austenite grain growth. To determine the grain refinement mechanism, partially solidified iron is quenched to capture early formation of austenite on nucleation sites and retain growth front of austenite grain in contact with liquid. Samples are analyzed using electron back scattered diffraction, scanning electron microscopy, energy dispersive X-ray, transmission electron microscopy, and selected area electron diffraction to understand the austenite grain refinement mechanism. The project evaluates processing-structure-property relationships in the grain refined nickel-alloyed ductile iron in the as-cast state. This foundational research is generalizable and could be applied to understand grain refinement mechanisms in other cast irons such as gray iron, compacted graphite iron, and white iron.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.

这项工程研究启动（ERI）资助使人们对镍合金球墨铸铁中细化奥氏体晶粒结构有了基本的了解。与钢和有色合金相比，球墨铸铁铸件易于通过既定的金属铸造工艺制造。球墨铸铁广泛用于生产汽车、农业、采矿、建筑、市政供水/下水道和国防工业中的结构部件，并且易于回收。本研究的目的是提供一种经济的方法来改善铸态球墨铸铁的机械性能，通过细化其晶粒组织，而不需要大量昂贵的合金元素添加剂或能源密集型热处理。该奖项支持基础研究，为开发奥氏体球墨铸铁的稳健原位晶粒细化工艺提供所需的知识。细化的晶粒组织提高了球墨铸铁的强度和韧性，这导致了更高的强度质量比铸件和更薄的截面和重量更轻的部件的发展。轻量化球墨铸铁件的好处是在生产、服务和回收过程中减少能源消耗和碳排放，这有利于美国经济和社会。这项研究涉及冶金、材料科学和制造等多个学科。多学科方法有助于扩大妇女和代表性不足的学生在研究中的参与，并对工程教育产生积极影响。球墨铸铁中奥氏体的细化可以导致更精细的最终显微组织，改善其机械性能。然而，在熔化和凝固过程中实现原位奥氏体晶粒细化的方法和相关机制还没有很好地理解。通过热力学平衡计算，设计了一种镍合金化球墨铸铁，使其在凝固过程中保持奥氏体组织。选择四种元素添加剂，铈、钛、铝和铋。假设所选择的合金添加剂通过促进奥氏体晶粒的异质成核或通过阻碍奥氏体晶粒生长来细化奥氏体微观结构。为了确定晶粒细化机制，将部分凝固的铁淬火以捕获在成核位点上的奥氏体的早期形成并保留与液体接触的奥氏体晶粒的生长前沿。利用电子背散射衍射、扫描电子显微镜、能量色散X射线、透射电子显微镜和选区电子衍射对样品进行分析，以了解奥氏体晶粒细化机制。本计画评估晶粒细化镍合金球墨铸铁在铸态下的制程-组织-性能关系。这项基础性研究是可推广的，并可应用于了解其他铸铁，如灰铁，蠕墨铸铁和白色铁晶粒细化机制。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。