CAREER: Understanding Interface Controlled Mechanisms of Recrystallization in Microstructurally Complex Mg Alloys

Ohio State University, The, Columbus OH

Investigators

Abstract

NON-TECHNICAL SUMMARY This Faculty Early Career Development Program (CAREER) grant will promote national scientific advancement through a research and education program that enables the mechanistic understanding of the multi-scale interactions that govern microstructural evolution in magnesium (Mg) and its alloys. Of the structural metals, Mg alloys, show great promise in vehicle weight reduction due to their lightness (two-thirds the density of aluminum), great strength-to-weight ratio, relatively low cost, and good castability and as a result can improve fuel efficiency in these components. Despite these advantages, the full adoption of Mg alloys in the automotive industry is limited by low ductility and poor formability and as a result Mg accounts for less than 1 percent of the average vehicle weight. These limitations have been historically linked to the microstructure that develops during thermomechanical processing but to date the mechanisms that influence this behavior are still unknown. The PI and their team will use a specifically designed, multi-modal methodology to understand the multi-scale interactions at interfaces associated with crystalline grains and deformation structures during recrystallization that govern crystallographic texture weakening in Mg alloys. The PI will establish several programs and initiatives that integrate the scientific research outcomes with their goal of broadening participation of under-represented and marginalized groups in materials science and engineering. The CAREER grant will support the development of a workshop focused on introducing concepts and opportunities in materials science to undergraduate students at historically black college and universities (HBCU), design and implement a cross-discipline course aimed at understanding the human cost of material-related engineering failures and implement a program providing resources in STEM to elementary school students within the Columbus, OH area. TECHNICAL SUMMARY This research program will critically advance the understanding of how the: 1). atomic structure near grain boundaries is altered by the presence of calcium (Ca) and zinc (Zn) and 2). dislocation interactions near specific interfaces associated with grains and deformation twins govern the nucleation and growth of strain-free grains during recrystallization as well as the 3). resulting mechanisms that govern orientation selection during growth of these recrystallized grains. The core hypothesis of this work is that recrystallization is driven by: 1) the formation of localized high strains and incompatibilities near and across twin boundaries (TB) and boundaries associated with crystalline grains and 2) changes in interface boundary mobility due to the preferential co-segregation of Ca and Zn to grain boundaries during thermomechanical processing promotes the nucleation and growth of recrystallized grains with randomized orientations. Correlation of recrystallization with boundaries or interfaces of varying type (i.e., mobility, energy) and misorientation provides important insight into the dominant texture weakening mechanisms in Mg alloys. The PI and team will use a specifically designed, multi-modal systematic investigation that employs a combination of high-resolution electron microscopy (transmission, scanning), high energy X-ray based techniques, and in-situ experimentation to understand and uncover the mechanisms that control recrystallization induced texture weakening. 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.