Shear Strength and Phase Transformations in Transition Metals and their Diborides under Terapascal Pressures

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PART 1: NON-TECHNICALThe transition metals (such as iron, manganese, copper and lesser known elements rhenium and osmium) and their alloys are widely used in aerospace, biomedical, and nuclear industries while transition metal diborides (one atom transition metal and 2 atoms of boron) have potential applications as high-strength structural materials under extreme conditions of stress, temperature, and corrosive environments. The application of high pressure on transition metals and their diborides is expected to yield novel structural modifications with desirable mechanical properties. The phase transformation studies and shear strength measurements on materials under high-pressures will be carried out using an innovative diamond anvil technology coupled to an x-ray synchrotron source. The computational calculations will use the state-of-the-art supercomputing facilities to predict stable crystal structures and their elastic properties and shear strength. This study will map out the crystalline phases and their shear strength with varying pressure with a goal of novel material synthesis that can be retained at ambient conditions for industrial applications. The project participants will receive extensive research and curriculum training in computational materials research and at the premier national facilities employing x-ray synchrotron radiation leading to a pipeline of trained scientific workforce in academia, national laboratories and industry. University of Alabama at Birmingham in partnership with the Historically Black Colleges and Universities in the southeastern region will jointly undertake efforts in broadening participation of underrepresented groups at all levels in the science and engineering fields.PART 2: TECHNICAL The study of phase transformations and shear strength measurements under high-pressures not only provides key-insights into mechanical properties under pressure but also provides a pathway to synthesizing novel materials under extreme conditions. The study of materials under extreme conditions has seen rapid progress recently with the attainment of near Terapascal (1 TPa = 1000 GPa) static pressures using toroidal single crystal diamond anvils and by employing two-stage nanocrystalline diamond micro-anvils. In addition, density functional theory has been applied to compute stable crystal structures and their elastic constants at high pressure for direct comparison with the experimental data on elastic moduli and shear strength under ultrahigh pressures. University of Alabama at Birmingham will perform phase transformations and shear strength measurements on rhenium (Re), osmium (Os), and their diborides ReB2 and OsB2 under both hydrostatic (helium pressure medium) and non-hydrostatic (no pressure medium) conditions. The ReB2 and OsB2 have high hardness values at ambient conditions in the range of 22-37 GPa and their shear strength variation with pressure is of considerable interest. The TPa pressure range is expected to cause significant electron transfer within the conduction band and possibly cause core-overlap leading to novel structural modifications with desirable mechanical properties. This study would provide crystal structure data and shear strength data for this unique electronic state of transition metals and their diborides under extreme conditions for direct comparison with the density functional calculations.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.