CAREER: Liquid Metal Processing of Magnesium Composites for Microstructure Refinement

该学院早期职业发展(CALEAR)奖支持研究，通过开发新的液态-金属加工策略，发现工艺-结构-性能关系，促进用于人体骨骼修复的镁植入物的现状，并旨在实现比目前可能的更大植入物所需的性能。生物可吸收镁植入物用于骨骼修复和组织加固，但大型植入物腐蚀太快，因此也会产生有害的氢气囊。这一问题将镁植入物限制在骨螺钉和冠状动脉支架等小型结构上。由于现有制造工艺不能充分控制腐蚀，镁及其合金目前不能用于全尺寸承重植入物应用。为了克服这些挑战，本研究将有助于了解和控制种植体制造过程中的组织演变，并通过创造更精细的组织来提高耐腐蚀性。这项名为严重超声波熔体剪切(SUM)的新工艺将使镁复合材料植入物的制造具有精细的微观结构和超低的均匀腐蚀。这项研究将有助于镁在整形外科、颅颌面、心血管、输尿管和食道植入物的大规模和小规模应用中的采用。它还将对冶金领域产生直接影响，该领域可以使用SUM工艺生产高质量的超细晶复合材料。研究活动将被整合到新的教育倡议中，在所有级别的学生中促进生物金属制造的高级教育，特别是西班牙裔学生。SUM过程通过将氧化膜分散到熔体中产生潜在的成核粒子，从而引发成核事件，从而导致颗粒细化。在熔体中同时诱导强烈的剪切和声学流动是为了解体和彻底分散增强纳米颗粒簇，导致微观结构均匀和减少熔体偏析。熔体中溶解的气体通过正向扩散进入空化气泡，使熔体脱气，从而消除了与气孔有关的铸造缺陷。研究小组将开发集成的计算和实验方法，以了解SUM过程的动力学，并为如何在镁复合材料熔体中实现高剪切和声空化提供见解。该奖项支持基础研究，以了解微观结构细化的机制，阐明微观结构如何改变腐蚀，并揭示超低均匀腐蚀的镁复合材料生产的指导原则。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。

This Faculty Early Career Development (CAREER) award supports research to advance the current state of magnesium implants for skeletal repair in humans by developing a new liquid-metal processing strategy, discovering process-structure-property relationships, and aiming to achieve the performance necessary for larger implants than are currently possible. Bioabsorbable magnesium implants are used in skeletal repairs and tissue reinforcement, but large implants corrode too rapidly and, as a result, also generate harmful hydrogen gas pockets. This problem limits the magnesium implants to small structures such as bone screws and coronary stents. Because corrosion can not be controlled adequately by existing manufacturing processes, magnesium and its alloys can not presently be used for full-size weight-bearing implant applications. To overcome these challenges, this research will help to understand and control the microstructural evolution during the implant manufacturing process and improve corrosion resistance by creating finer microstructures. The new process, called Severe Ultrasonic Melt Shearing (SUMS), will enable manufacturing of magnesium composite implants with refined microstructure and ultra-low uniform corrosion. The research will aid the adoption of magnesium in large-scale and small-scale applications for orthopedic, craniomaxillofacial, cardiovascular, ureteral, and esophageal implants. It also will have a direct impact on the field of metallurgy, which can use the SUMS process for production of high-quality, ultrafine-grained composites. Research activities will be integrated into new educational initiatives that promote advanced education about biometals manufacturing among students at all levels, with special attention to Hispanic students.The SUMS process creates potential nucleating particles by dispersing oxide films into the melt that can initiate the nucleation events, resulting in the grain refinement. Simultaneous induction of intensive shearing and acoustic streaming in the melt is meant to disintegrate and thoroughly disperse the clusters of reinforcing nanoparticles, resulting in microstructure homogeneity and reduced melt segregation. The rectified diffusion of the dissolved gas in melt into the cavitation bubbles can de-gas the melt, resulting in the elimination of casting-induced defects related to gas porosity. The research team will develop integrated computational and experimental approaches to understand the dynamics of the SUMS process and provide insight into how to achieve high shearing and acoustic cavitation in the magnesium composite melt. The award supports fundamental research to understand the mechanisms of microstructural refinement, elucidate how microstructure can alter corrosion, and unravel the guiding principles of magnesium composite production with ultra-low uniform corrosion.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.