KSEF R&D Excellence: Geometrically Nedcessary Dislocation in Polycrystals: Their Experimental Recovery and Effects on Plastic Anisotropy

~Ietals are usually polycrystalline: they are aggregates of tiny grains of yarious orientations. sizes, and shapes. The orientations of the grains and their stereology (i.e.. how the!' arc arranged in space) constitute the meso-scale structure of a polycrystal. On a finer scale, the grains themselves also haye microstructures (e.g.. distributions of dislocations). Together with chemical composition, the meso- and micro-scale structures of a metal determine its macroscopic mechanical properties, including its formability. The technology of Field Emission Gun Scanning Electron '.Iicroscope \,it h Electron Backscatter Diffraction (FEGSE~I-EBSD) has made enormous advances recently. \Vith the state-of-the-art FEGSElIl-EBSD equipment. we contend that not only the meso-scale structure but also the dislocation tensor of a polycrystal1ine metal can be determined, thus opening up n('\\' forefronts of research with broad impact. This proposed project comprises three preliminary jexploratory studies. with a yiew to the deyelopment of three ful1-ftedged research programs with objectiyes as fol1ows: . to design a protocol for recO\'ery of the dislocation tensor of a polyerystal1ine sample through EBSD measurement of the lattice curyature in its grains; . to deyelop a theory for recO\'ery of the dislocation tensor through ultrasonic measurernents: . to deyise a plastic potential that includes the dislocation tensor as an independent Yariable and would adequately model the behm'ior of continuous-cast .5000 series aluminum alloys in met al forming operations. The first program is central to a subject of great interest to many in the materials science community. The second should be of interest to the community in nondestructive evaluation. where applications of ultrasound in characterization of material microstructures haye become a hot theme. The third further deyelops joint research projects of the PI with colleagues at the Uniyersity of Kentucky, which are supported by AFOSR and 0JSF. Commonwealth Aluminum Concast. Inc. (CACI) is the industrial partner of one of the projects. Key Words: multiscale modeling: orientation imaging microscop!': geometrically necessary dislocations; nltrasonic measurement of dislocations: plastic potential.