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

过渡金属(如铁、锰、铜和鲜为人知的元素Re和Om)及其合金广泛应用于航空航天、生物医学和核工业，而过渡金属二硼化物(一个原子的过渡金属和两个原子的硼)在极端的应力、温度和腐蚀环境下作为高强度结构材料具有潜在的应用前景。对过渡金属及其二硼化物施加高压有望产生具有理想机械性能的新型结构修饰。高压下材料的相变研究和剪切强度测量将使用与X射线同步加速器源相耦合的创新的金刚石顶锤技术来进行。计算计算将使用最先进的超级计算设备来预测稳定的晶体结构及其弹性性质和剪切强度。这项研究将绘制晶相及其在不同压力下的剪切强度图，目标是合成可在环境条件下保留的新型材料，用于工业应用。项目参与者将在计算材料研究和使用x射线同步辐射的主要国家设施接受广泛的研究和课程培训，从而在学术界、国家实验室和工业中培养训练有素的科学工作人员。阿拉巴马大学伯明翰分校将与东南地区历史上的黑人学院和大学合作，共同努力扩大在科学和工程领域各级代表不足的群体的参与。第2部分：技术高压下的相变和剪切强度测量的研究不仅提供了对压力下机械性能的关键见解，还提供了在极端条件下合成新型材料的途径。最近，极端条件下材料的研究取得了快速进展，使用环形单晶金刚石锤和两级纳米晶金刚石微锤，达到了接近Terapascal(1 tpa=1000 Gpa)的静态压力。此外，还用密度泛函理论计算了稳定的晶体结构及其在高压下的弹性常数，并与超高压下的弹性模量和剪切强度的实验数据进行了直接比较。阿拉巴马大学伯明翰分校将在流体静力(氦压力介质)和非流体静力(无压力介质)条件下对Re(Re)、Os(Os)及其二硼化物ReB2和OsB2进行相变和剪切强度测量。在环境条件下，ReB2和OsB2具有较高的硬度值，其剪切强度随压力的变化是相当有意义的。TPA压力范围有望在导带内引起显着的电子转移，并可能导致核心重叠，从而产生具有理想机械性能的新型结构修饰。这项研究将提供过渡金属及其二硼化物在极端条件下这种独特的电子状态的晶体结构数据和剪切强度数据，以便直接与密度泛函计算进行比较。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.