Collaborative Research: Computational and experimental study of alloying effects on <c+a> slip in Mg alloys

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Nontechnical Summary:By virtue of their low density, Magnesium (Mg) and Mg-rich alloys are of significant interest in lightweight vehicle technology. However the ability to form these materials into useful shapes at ambient temperature has been the Achilles heel to widespread implementation. The room temperature formability and damage tolerance are essential to making the cost of Mg alloys competitive with those of aluminum alloys and steels. These properties rely on the ease of plastic deformation, a phenomenon that is mediated by atomic level processes. This research effort provides a fundamental understanding of how the atomic processes, responsible for enhanced formability, can be facilitated through addition of alloying elements. Furthermore, the integrated computational/experimental methodology developed by this program is a crucial step towards physics-based predictive alloy design compared to the traditional empirical approach based on trial and error and can be applied to a range of other metallic systems with similar crystal structure, such as technologically important Ti and Zr alloys. Moreover, the education and outreach component of this program, are aimed at (1) incorporating computational modeling in classroom to enhance learning of difficult concepts, (2) preparing materials science and engineering students for future careers with an increased importance of computational modeling and (3) fostering enthusiasm about Science, Technology Engineering and Math (STEM) fields in students, particularly from underrepresented groups. This project has an outreach program component in collaboration with the college of Engineering at the Ohio State University.Technical Summary:The overarching goal of this program is to enhance the room temperature deformability of Mg alloys. In pursuit of the above goal, this project aims to activate the c+a slip mode through favorable alloying. Electronic-structure calculations of c+a dislocation cores will be used to (1) Identify solutes that would stabilize the glissile core geometry of the c+a edge dislocations (2) Study the effect of candidate elements on the stability and cross-slip rate of c+a screw dislocations. Elements that promote the slip of edge segments without compromising the motion of screw segments will be suggested as viable candidates. The consequence of the theoretical alloying suggestions will be evaluated experimentally by (3) making single crystals of the proposed alloys (4) measuring stress-strain curves and (5) characterizing dislocation structure evolution. The outcome will provide new understanding of solute effects on easier activation of non-basal deformation modes in Mg that can then enhance room temperature ductility of Mg alloys, thereby increasing the widespread use of these lightweight alloys.