CAREER: Liquid Metal Processing of Magnesium Composites for Microstructure Refinement

The University Of Central Florida Board Of Trustees, Orlando FL

Investigators

Abstract

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.