TECHNICAL: PI's have made several key discoveries that pave the way to develop new hexagonal metal based alloys that not only combine high yield points and high damping capabilities but can also be used to self-monitor their stress state. The breakthrough that allows PI to conduct this high-risk/high-payoff and transformative work is the identification of a large class of solids labeled as kinking nonlinear elastic, (KNE) solids, because one of their important (and in many cases only) deformation mode is the formation of fully reversible, dislocation-based incipient kink bands, IKBs, that at higher stresses and/or temperatures devolve into mobile dislocation walls, MDW, viz. low angle grain boundaries and plastic deformation. The coalescence of the latter leads to the formation of kink boundaries (KBs). PI has shown that the IKB to MDW transformation coincides with the yield points of some hexagonal metals, such as Mg, Co and Ti. The MDW to KB transformation, on the other hand, reduces the domain size and leads to hardening. While currently PI understands the effects of IKBs, MDW and ultimately KBs on the mechanical properties and damping, PI has not done so systematically, because to date PI's focus has been on identifying and classifying KNE solids. In other words, little was done in terms of making use of newly gained knowledge to engineer solids with exceptional properties. In this work PI will do just that by systematically studying the effects of microstructure (e.g. grain size, texture, porosity), chemistry (e.g. solid solutions, second phases) and thermo-mechanical processing (e.g. pre-strains at cryogenic, room and higher temperatures, creep) on the nucleation and growth of IKBs, MDW and KBs in some important hexagonal metals such as Mg, Ti, Co and their alloys. To carry out the latter PI will use the following experimental techniques: simple compressive and tensile testing, cyclic spherical nano-indentations, electron-backscattered diffraction, in situ TEM and SEM, acoustic coupling technique, (ACT) and resonant ultrasound spectroscopy (RUS), and in situ neutron and XRD diffraction. For KNE solids, there is a one-to-one correspondence between stress or strain and sound attenuation. Thus by monitoring the latter, the health of a structural component made with a KNE solid - or if a KNE solid is affixed to a structural component - can be easily monitored as a function of time. This self-stress monitoring capability can - depending on material chosen - be useful over extended temperature regimes and/or corrosive environments. NON-TECHNICAL: Most importantly, PI notes that IKBs are one of the last few, but crucial missing pieces in the deformation-of-solids puzzle; this work would allow PI to outline the shape of this missing piece. From a perusal of the elements and compounds that are KNE it is apparent that most of nature is indeed KNE. Thus what is learned in this work will have important ramifications and implications in many other fields of inquiry, from geology to microelectronics and device manufacturers. The work is structured in such a way that graduate and undergraduate (UG) students work closely together. UG benefit from the excitement of discovery, and learn useful analytic and other skills. For the graduate student this cross-fertilization creates better graduate students, mentors, teachers, leaders and scientists. Another major goal of this project will be to convince a majority, if not all, of the carefully chosen UG students working on this project to go for graduate degrees in the sciences in general, and materials science in particular.
