Hardness and Elasticity of Superhard and Ultrahard Materials

Overview: Page A This proposal explores the divide between the hardest known substance (diamond) and the widely available (but nearly half as hard) cubic-boron nitride (c-BN) through design, synthesis, and characterization of superhard materials in the B-C-N system. The research plan capitalizes on the latest materials characterization technology available at Northwestern’s research centers, the nearby Advanced Photon Source, and features a method unique to the PI’s laboratory, GHz-ultrasonic interferometry, for determining the elastic moduli of experimental products. Using high-pressure high-temperature synthesis, single-crystals of BCxN across the solid solution have already been produced. Proposed research will determine their compositions to target materials with a combination of the highest hardness and thermal stability for in-depth physical properties measurements and synthesis in more versatile nano-polycrystalline (NP) forms. Micro and nano-hardness tests will be performed and analyzed using 3D optical microscopy. Structures and compositions will be evaluated by high-resolution electron microscopy techniques. Using the high-precision GHz-ultrasonic interferometry, as well as Brillouin spectroscopy, the measured shear moduli of BCxN materials as a function of composition (x) and pressure (P) will further establish trends that point to the hardest composition. Intellectual Merit : Superhard materials, presently defined as those having Vicker’s hardness (HV) >40 GPa, are widely sought after in science and technological applications, especially as anvils, abrasives, and cutting tools. Can a better diamond-like material be created? And how will it be recognized, i.e. proved as such? Those challenges are addressed in this proposal by designing and creating new compounds (some already synthesized but poorly characterized, others predicted theoretically) in the B-C-N system, especially along the BCxN join. Through analytical methods performed on single-crystal and nano-polycrystalline run products, trends between bonding type, composition, pressure, temperature, elastic properties and hardness will be experimentally determined and provide fundamental input to theoretical studies of superhard materials. Newly applied to superhard materials, the PI?s unique GHz-ultrasonic system will not only be used to measure high-precision elastic properties of synthesis products from this study, but potentially also on novel superhard materials emanating from other researchers worldwide through collaborative opportunities created by the proposed research. Ultimately, BCxN compounds possessing the highest combination of hardness and thermal stability may result in creation of a material rivaling diamond for future applications in science and technology. Broader Impacts : The PI’s interdisciplinary research in mineral physics spans high-pressure materials science, solid-Earth geophysics and geochemistry, and condensed matter physics. The postdoc, graduate students, and undergraduates involved in this study will therefore be exposed to wide range of science with career opportunities in academia, the National labs, and industry. This proposal would fund one postdoctoral researcher who is on a trajectory for a faculty position in materials science. In addition to graduate students, the PI will maintain at least one undergraduate researcher on the project. Science education and outreach will occur at all levels. At the K-8 level, new modules in materials science will be created for 3-4th grade students of Project