Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session Q4: NT.1 Superhard Materials II |
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Chair: Peter Pauzauskie, University of Washington Room: Vashon |
Wednesday, July 10, 2013 1:45PM - 2:15PM |
Q4.00001: Synthesis and Characterization of Low-Cost Superhard Transition-Metal Borides Invited Speaker: Richard Kaner The increasing demand for high-performance cutting and forming tools, along with the shortcomings of traditional tool materials such as diamond (unable to cut ferrous materials), cubic boron nitride (expensive) and tungsten carbide (relatively-low hardness), has motivated the search for new superhard materials for these applications. This has led us to a new class of superhard materials, dense refractory transition-metal borides, which promise to address some of the existing problems of conventional superhard materials. For example, we have synthesized rhenium diboride (ReB$_{\mathrm{2}})$ using arc melting at ambient pressure. This superhard material has demonstrated an excellent electrical conductivity and superior mechanical properties, including a Vickers hardness of 48.0 GPa (under an applied load of 0.49 N). To further increase the hardness and lower the materials costs, we have begun exploring high boron content metal borides including tungsten tetraboride (WB$_{\mathrm{4}})$. We have synthesized WB$_{\mathrm{4}}$ by arc melting and studied its hardness and high-pressure behavior. With a similar Vickers hardness (43.3 GPa under a load of 0.49 N) and bulk modulus (326-339 GPa) to ReB$_{\mathrm{2}}$, WB$_{\mathrm{4}}$ offers a lower cost alternative and has the potential to be used in cutting tools. To further enhance the hardness of this superhard metal, we have created the binary and ternary solid solutions of WB$_{\mathrm{4}}$ with Cr, Mn and Ta, the results of which show a hardness increase of up to 20 percent. As with other metals, these metallic borides can be readily cut and shaped using electric discharge machining (EDM). [Preview Abstract] |
Wednesday, July 10, 2013 2:15PM - 2:30PM |
Q4.00002: Novel metal borides: structure, high-pressure behavior and properties. Elena Bykova, Huiyang Gou, Michael Hanfland, Artem Abakumov, Natalia Dubrovinskaia, Leonid Dubrovinsky Metal borides are an important class of compounds having a number of remarkable properties like superconductivity, low compressibility, and high hardness. Therefore synthesis of novel metal borides and their investigations have a great interest for materials science and technology. Novel metal borides, FeB$_{4}$, Fe$_{2}$B$_{7}$, FeB$_{50}$, and MnB$_{4}$, have been obtained in a series of high pressure and high temperature experiments in multi-anvil apparatus. The current work is focused on their crystal structures determined by single crystal X-ray diffraction and physical properties, such as compressibility and hardness. Rather low compressibility of all studied iron borides has been revealed in X-ray diffraction experiments in diamond anvil cells where single crystals were compressed up to 40-50 GPa. In particular, bulk modulus of FeB$_{4}$ was found to be K$=$252(5) GPa. This value correlates very well with a very high hardness (Hv$=$65(5) GPa) of this material. Additionally, FeB$_{4}$ shows phonon-mediated superconductivity below 2.9 K, thus opening a class of novel materials with a highly desirable combination of physical properties. [Preview Abstract] |
Wednesday, July 10, 2013 2:30PM - 2:45PM |
Q4.00003: New hybrid materials from compressing intercalated fullerides Mingguang Yao, Bingbing Liu, Wen Cui, Junping Xiao Upon compression, molecular crystal undergoes complicated transformations, including the crystal structure, molecular morphology, and inter- and intra-molecular bonding. Here, we studied a series of two-component fullerides composed of C60 molecules and various dopants under pressure and demonstrate the effect of the dopants on the structural evolution of C60s upon compression. C60 molecules are found to behave similarly, deformed and even collapsed at critical pressures, while the different interactions between the intercalated dopants and C60s result in different properties of the phases formed at high pressure. A class of new hybrid structures has been fabricated, in which several superhard phases have been discovered. The underlying mechanism for the superhard phase formation has been further uncovered. [Preview Abstract] |
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