Three-Dimensional Characterization and Simulation of Deformation in Hexagonal Metals

Michigan State University, East Lansing MI

Investigators

Abstract

Many lightweight metals such as magnesium, titanium, and zirconium alloys have a hexagonal crystal structure, which is unique from the cubic structures of commonly used aluminum and steel alloys. The room-temperature deformation of hexagonal metals is often dominated by a process known as mechanical twinning, wherein atoms shift positions to a highly symmetric arrangement in order to accommodate an applied stress or load. How mechanical twinning operates in such commercially-relevant, structurally-loaded, hexagonal metals is presently not fully understood and, therefore, limits the computational design of such materials and their manufacturing processes. An improved understanding can accelerate their development, reduce associated costs, and provide enhanced reliability of manufactured components. This award supports research towards the understanding of deformation of these technologically important materials, which have application in lightweight automotive and aerospace components, as well as many other structural applications where high strength and low weight are critical. At the fundamental level, the controlling factor in the mechanical behavior of structural metals is the resistance of the crystal lattice to motion of dislocations, formation of mechanical twins, and displacive phase transformations. Particularly in hexagonal metals and alloys (Mg, Ti, Zr), which lack easily activated dislocation slip systems, mechanical twinning is prominent to accommodate plastic deformation. In this research program, the evolving twin structure in such metals is comprehensively characterized in three dimensions (3D) to gain novel insights and interpretations on the formation and propagation of twins and their relation to, for instance, parent grain orientation or grain boundary character distribution. The data will be used to validate constitutive descriptions of twin formation by incorporating the 3D microstructural information into full-field crystal plasticity simulations at high spatial resolution. Thus, this work provides a more complete understanding of how twins form and can fill in the presently missing knowledge to more confidently model the contribution of mechanical twinning to plastic deformation.